Publications by authors named "Han Houdijk"

66 Publications

General estimates of the energy cost of walking in people with different levels and causes of lower-limb amputation: a systematic review and meta-analysis.

Prosthet Orthot Int 2021 Sep 17. Epub 2021 Sep 17.

Heliomare Research and Development, Wijk aan Zee, the Netherlands Amsterdam Movement Science, Faculty of Behavioral and Movement Sciences, Vrije Universiteit Amsterdam, Amsterdam, the Netherlands Department of Clinical Sciences, Division of Physiotherapy, Brunel University London, London, United Kingdom University of Groningen, University Medical Center Groningen, Center for Human Movement Sciences, Groningen, the Netherlands.

Background: Energy cost of walking (ECw) is an important determinant of walking ability in people with a lower-limb amputation. Large variety in estimates of ECw has been reported, likely because of the heterogeneity of this population in terms of level and cause of amputation and walking speed.

Objectives: To assess (1) differences in ECw between people with and without a lower-limb amputation, and between people with different levels and causes of amputation, and (2) the association between ECw and walking speed.

Study Design: Systematic review and meta-analysis.

Methods: We included studies that compared ECw in people with and without a lower-limb amputation. A meta-analysis was done to compare ECw between both groups, and between different levels and causes of amputation. A second analysis investigated the association between self-selected walking speed and ECw in people with an amputation.

Results: Out of 526 identified articles, 25 were included in the meta-analysis and an additional 30 in the walking speed analysis. Overall, people with a lower-limb amputation have significantly higher ECw compared to people without an amputation. People with vascular transfemoral amputations showed the greatest difference (+102%) in ECw. The smallest difference (+12%) was found for people with nonvascular transtibial amputations. Slower self-selected walking speed was associated with substantial increases in ECw.

Conclusion: This study provides general estimates on the ECw in people with a lower-limb amputation, quantifying the differences as a function of level and cause of amputation, as well as the relationship with walking speed.
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http://dx.doi.org/10.1097/PXR.0000000000000035DOI Listing
September 2021

Mobile App (WHEELS) to Promote a Healthy Lifestyle in Wheelchair Users With Spinal Cord Injury or Lower Limb Amputation: Usability and Feasibility Study.

JMIR Form Res 2021 08 9;5(8):e24909. Epub 2021 Aug 9.

see Acknowledgments, .

Background: Maintaining a healthy lifestyle is important for wheelchair users' well-being, as it can have a major impact on their daily functioning. Mobile health (mHealth) apps can support a healthy lifestyle; however, these apps are not necessarily suitable for wheelchair users with spinal cord injury or lower limb amputation. Therefore, a new mHealth app (WHEELS) was developed to promote a healthy lifestyle for this population.

Objective: The objectives of this study were to develop the WHEELS mHealth app, and explore its usability, feasibility, and effectiveness.

Methods: The WHEELS app was developed using the intervention mapping framework. Intervention goals were determined based on a needs assessment, after which behavior change strategies were selected to achieve these goals. These were applied in an app that was pretested on ease of use and satisfaction, followed by minor adjustments. Subsequently, a 12-week pre-post pilot study was performed to explore usability, feasibility, and effectiveness of the app. Participants received either a remote-guided or stand-alone intervention. Responses to semistructured interviews were analyzed using content analysis, and questionnaires (System Usability Score [SUS], and Usefulness, Satisfaction, and Ease) were administered to investigate usability and feasibility. Effectiveness was determined by measuring outcomes on physical activity, nutrition, sleep quality (Pittsburgh Sleep Quality Index), body composition, and other secondary outcomes pre and post intervention, and by calculating effect sizes (Hedges g).

Results: Sixteen behavior change strategies were built into an app to change the physical activity, dietary, sleep, and relaxation behaviors of wheelchair users. Of the 21 participants included in the pilot study, 14 participants completed the study. The interviews and questionnaires showed a varied user experience. Participants scored a mean of 58.6 (SD 25.2) on the SUS questionnaire, 5.4 (SD 3.1) on ease of use, 5.2 (SD 3.1) on satisfaction, and 5.9 (3.7) on ease of learning. Positive developments in body composition were found on waist circumference (P=.02, g=0.76), fat mass percentage (P=.004, g=0.97), and fat-free mass percentage (P=.004, g=0.97). Positive trends were found in body mass (P=.09, g=0.49), BMI (P=.07, g=0.53), daily grams of fat consumed (P=.07, g=0.56), and sleep quality score (P=.06, g=0.57).

Conclusions: The WHEELS mHealth app was successfully developed. The interview outcomes and usability scores are reasonable. Although there is room for improvement, the current app showed promising results and seems feasible to deploy on a larger scale.
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http://dx.doi.org/10.2196/24909DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8386360PMC
August 2021

The relationship between relative aerobic load, energy cost, and speed of walking in individuals post-stroke.

Gait Posture 2021 Sep 21;89:193-199. Epub 2021 Jul 21.

Department of Human Movement Sciences, Faculty of Behavioural and Movement Sciences, Vrije Universiteit Amsterdam, Amsterdam Movement Sciences, the Netherlands; Heliomare Research and Development, Wijk aan Zee, the Netherlands; University of Groningen, University Medical Center Groningen, Center for Human Movement Sciences, Groningen, the Netherlands.

Background: Individuals post-stroke walk slower than their able-bodied peers, which limits participation. This might be attributed to neurological impairments, but could also be caused by a mismatch between aerobic capacity and aerobic load of walking leading to an unsustainable relative aerobic load at most economic speed and preference for a lower walking speed.

Research Question: What is the impact of aerobic capacity and aerobic load of walking on walking ability post-stroke?

Methods: Forty individuals post-stroke (more impaired N = 21; preferred walking speed (PWS)<0.8 m/s, less impaired N = 19), and 15 able-bodied individuals performed five, 5-minute treadmill walking trials at 70 %, 85 %, 100 %, 115 % and 130 % PWS. Energy expenditure (mlO/kg/min) and energy cost (mlO/kg/m) were derived from oxygen uptake (V˙O). Relative load was defined as energy expenditure divided by peak aerobic capacity (%V˙Opeak) and by V˙O at ventilatory threshold (%V˙O-VT). Relative load and energy cost at PWS were compared with one-way ANOVA's. The effect of speed on these parameters was modeled with Generalized Estimating Equations.

Results: Both more and less impaired individuals post-stroke showed lower PWS than able-bodied controls (0.44 [0.19-0.76] and 1.04 [0.81-1.43] vs 1.36 [0.89-1.53] m/s) and higher relative load at PWS (50.2 ± 14.4 and 51.7 ± 16.8 vs 36.2 ± 7.6 %V˙Opeak and 101.9 ± 20.5 and 97.0 ± 27.3 vs 64.9 ± 13.8 %V˙O-VT). Energy cost at PWS of more impaired (0.30 [.19-1.03] mlO/kg/m) was higher than less-impaired (0.19[0.10-0.24] mlO/kg/m) and able-bodied (0.15 [0.13-0.18] mlO/kg/m). For post-stroke individuals, increasing walking speed above PWS decreased energy cost, but resulted in a relative load above endurance threshold.

Significance: Individuals post-stroke seem to reduce walking speed to prevent unsustainably high relative aerobic loads at the expense of reduced economy. When aiming to improve walking ability post-stroke, it is important to consider training aerobic capacity.
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http://dx.doi.org/10.1016/j.gaitpost.2021.07.012DOI Listing
September 2021

RehabMove2018: active lifestyle for people with physical disabilities; mobility, exercise & sports.

Disabil Rehabil 2021 Jun 29:1-2. Epub 2021 Jun 29.

Department of Human Movement Sciences, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.

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http://dx.doi.org/10.1080/09638288.2021.1940319DOI Listing
June 2021

How does external lateral stabilization constrain normal gait, apart from improving medio-lateral gait stability?

R Soc Open Sci 2021 Mar 24;8(3):202088. Epub 2021 Mar 24.

Department of Human Movement Sciences, Faculty of Behavioural and Movement Sciences, Vrije Universiteit Amsterdam, Amsterdam Movement Sciences, van der Boechorststraat 9, Amsterdam, NL-1081 BT, The Netherlands.

Background: The effect of external lateral stabilization on medio-lateral gait stability has been investigated previously. However, existing lateral stabilization devices not only constrain lateral motions but also transverse and frontal pelvis rotations. This study aimed to investigate the effect of external lateral stabilization with and without constrained transverse pelvis rotation on mechanical and metabolic gait features.

Methods: We undertook two experiments with 11 and 10 young adult subjects, respectively. Kinematic, kinetic and breath-by-breath oxygen consumption data were recorded during three walking conditions (normal walking (Normal), lateral stabilization with (Free) and without transverse pelvis rotation (Restricted)) and at three speeds (0.83, 1.25 and 1.66 m s) for each condition. In the second experiment, we reduced the weight of the frame, and allowed for longer habituation time to the stabilized conditions.

Results: External lateral stabilization significantly reduced the amplitudes of the transverse and frontal pelvis rotations, in addition to medio-lateral, anterior-posterior, and vertical pelvis displacements, transverse thorax rotation, arm swing, step length and step width. The amplitudes of free vertical moment, anterior-posterior drift over a trial, and energy cost were not significantly influenced by external lateral stabilization. The removal of pelvic rotation restrictions by our experimental set-ups resulted in normal frontal pelvis rotation in Experiment 1 and significantly higher transverse pelvis rotation in Experiment 2, although transverse pelvis rotation still remained significantly less than in the Normal condition. Step length increased with the increased transverse pelvis rotation.

Conclusion: Existing lateral stabilization set-ups not only constrain medio-lateral motions (i.e. medio-lateral pelvis displacement) but also constrain other movements such as transverse and frontal pelvis rotations, which leads to several other gait changes such as reduced transverse thorax rotation, and arm swing. Our new set-ups allowed for normal frontal pelvis rotation and more transverse pelvis rotation (yet less than normal). However, this did not result in more normal thorax rotation and arm swing. Hence, to provide medio-lateral support without constraining other gait variables, more elaborate set-ups are needed.
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http://dx.doi.org/10.1098/rsos.202088DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8074891PMC
March 2021

Estimation of Metabolic Energy Expenditure during Short Walking Bouts.

Int J Sports Med 2021 Apr 16. Epub 2021 Apr 16.

Department of Human Movement Sciences, Faculty of Behavioural and Movement Sciences, Amsterdam Movement Sciences, Vrije Universiteit Amsterdam, Amsterdam, Netherlands.

Assessment of metabolic energy expenditure from indirect calorimetry is currently limited to sustained (>4 min) cyclic activities, because of steady-state requirements. This is problematic for patient populations who are unable to perform such sustained activities. Therefore, this study explores validity and reliability of a method estimating metabolic energy expenditure based on oxygen consumption (V̇O) during short walking bouts. Twelve able-bodied adults twice performed six treadmill walking trials (1, 2 and 6 min at 4 and 5 km/h), while V̇O was measured. Total V̇O was calculated by integrating net V̇O over walking and recovery. Concurrent validity with steady-state V̇O was assessed with Pearson's correlations. Test-retest reliability was assessed using intra-class correlation coefficients (ICC) and Bland-Altman analyses. Total V̇O was strongly correlated with steady-state V̇O (r=0.91-0.99), but consistently higher. Test-retest reliability of total V̇O (ICC=0.65-0.92) was lower than or comparable to steady-state V̇O (ICC=0.83-0.92), with lower reliability for shorter trials. Total V̇O discriminated between gait speeds. Total oxygen uptake provides a useful measure to estimate metabolic load of short activities from oxygen consumption. Although estimates are less reliable than steady-state measurements, they can provide insight in the yet unknown metabolic demands of daily activities for patient populations unable to perform sustained activities.
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http://dx.doi.org/10.1055/a-1373-5770DOI Listing
April 2021

Effects of Handrail and Cane Support on Energy Cost of Walking in People With Different Levels and Causes of Lower Limb Amputation.

Arch Phys Med Rehabil 2021 07 5;102(7):1340-1346.e3. Epub 2021 Mar 5.

Amsterdam Movement Science, Faculty of Behavioral and Movement Sciences, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands.

Objective: The energy cost of walking with a lower limb prosthesis is higher than able-bodied walking and depends on both cause and level of amputation. This increase might partly be related to problems with balance control. In this study we investigated to what extent energy cost can be reduced by providing support through a handrail or cane and how this depends on level and cause of amputation.

Design: Quasi-experimental study.

Setting: Rehabilitation gait laboratory.

Participants: Twenty-six people with a lower limb amputation were included: 9 with vascular and 17 with nonvascular causes, 16 at transtibial, and 10 at transfemoral or knee disarticulation level (N=26).

Interventions: Participants walked on a treadmill with and without handrail support and overground with and without a cane.

Main Outcome Measures: Energy cost was assessed using respirometry.

Results: On the treadmill, handrail support resulted in a 6% reduction in energy cost on average. This effect was attributed to an 11% reduction in those with an amputation attributable to vascular causes, whereas the nonvascular group did not show a significant difference. No interaction with level of amputation was found. Overground, no main effect of cane support was found, although an interaction effect with cause of amputation demonstrated a small nonsignificant decrease in energy cost (3%) in the vascular group and a significant increase (6%) in the nonvascular group when walking with a cane. The effect of support was positively correlated with self-selected walking speed.

Conclusions: This study demonstrates that providing external support can contribute to a reduction in energy cost in people with an amputation due to vascular causes with reduced walking ability while walking in the more challenging condition of the treadmill. Although it is speculated that this effect might be related to problems with balance control, this will need further investigation.
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http://dx.doi.org/10.1016/j.apmr.2021.02.007DOI Listing
July 2021

[Exercise capacity after mechanical ventilation because of COVID-19: Cardiopulmonary exercise tests in clinical rehabilitation].

Ned Tijdschr Geneeskd 2020 10 29;164. Epub 2020 Oct 29.

Sport- en Beweegkliniek, Haarlem.

Objective: To safely and effectively train the exercise capacity of post-COVID-19 patients it is important to test for cardiopulmonary risk factors and to assess exercise limitations. The goal of this study was to describe the exercise capacity and underlying exercise limitations of mechanically ventilated post-COVID-19 patients in clinical rehabilitation.

Design: A retrospective cohort study.

Method: Twenty-four post-COVID-19patients that were mechanically ventilated at ICU and thereafter admitted for clinical rehabilitation performed a symptom-limited cardiopulmonary exercise test (CPET) with breath-by-breath gas-exchange monitoring, ECG-registration, blood pressure- and saturation monitoring. In absence of a primary cardiac or ventilatory exercise limitation patients were considered to be limited primarily by decreased peripheral muscle mass.

Results: Twenty-three patients could perform a maximal exercise test and no adverse events occurred. Cardiorespiratory fitness was very poor with a median peak oxygen uptake of 15.0 [10.1-21.4] mlO2/kg/min (57% of predicted values). However, we observed large differences within the group in both exercise capacity and exercise limitations. While 7/23 patients were primarily limited by ventilatory function, the majority (70%) was limited primarily by the decreased peripheral muscle mass.

Conclusion: Cardiorespiratory fitness of post-COVID-19 patients in clinical rehabilitation is strongly deteriorated. The majority of patients seemed primarily limited for exercise by the decreased peripheral muscle mass.
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October 2020

Intraobserver Reliability and Construct Validity of the Squat Test in Children With Cerebral Palsy.

Pediatr Phys Ther 2020 10;32(4):399-403

Department of Rehabilitation Medicine (Drs Eken, Dallmeijer, Buizer, van Hutten, Piening, and van der Krogt), Amsterdam Movement Sciences, Amsterdam UMC, Vrije Universiteit Amsterdam, Amsterdam, the Netherlands; Division of Orthopaedic Surgery (Dr Eken), Department of Surgical Sciences, Faculty of Stellenbosch University, Tygerberg Campus, Tygerberg, South Africa; Heliomare Rehabilitation Center (Mrs Hogervorst and Dr Houdijk), Wijk aan Zee, the Netherlands; Department of Human Movement Sciences (Dr Houdijk), Faculty of Behaviour and Movement Sciences, Amsterdam Movement Sciences, Vrije Universiteit Amsterdam, Amsterdam, the Netherlands.

Purpose: This study evaluated intraobserver reliability and construct validity of the squat test to assess lower extremity strength in children with cerebral palsy (CP) and spastic diplegia.

Methods: Children with CP performed 2 trials of the squat test and calculated the intraclass correlation coefficient to evaluate intraobserver reliability. Correlations between outcomes of hand-held dynamometry (HHD) of knee extensor strength and an 8-repetition maximum (8RM) leg press test and the squat test were calculated to evaluate construct validity.

Results: Excellent intraobserver reliability was observed for the squat test. Correlations between squat test performance and HHD knee extension and 8RM leg press test demonstrated good construct validity.

Conclusions: The squat test is a reliable and valid tool to assess lower extremity strength in children with CP and spastic diplegia. The squat test is inexpensive and less time-consuming, and therefore particularly suitable for clinicians.
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http://dx.doi.org/10.1097/PEP.0000000000000736DOI Listing
October 2020

Rehabilitation: mobility, exercise & sports; a critical position stand on current and future research perspectives.

Disabil Rehabil 2020 Aug 17:1-16. Epub 2020 Aug 17.

Center for Human Movement Sciences, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands.

Background: Human movement, rehabilitation, and allied sciences have embraced their ambitions within the cycle of "RehabMove" congresses over the past 30 years. This combination of disciplines and collaborations in the Netherlands has tried to provide answers to questions in the fields of rehabilitation and adapted sports, while simultaneously generating new questions and challenges. These research questions help us to further deepen our understanding of (impaired) human movement and functioning, with and without supportive technologies, and stress the importance of continued multidisciplinary (inter)national collaboration.

Methods: This position stand provides answers that were conceived by the authors in a creative process underlining the preparation of the 6th RehabMove Congress.

Results: The take-home message of the RehabMove2018 Congress is a plea for continued multidisciplinary research in the fields of rehabilitation and adapted sports. This should be aimed at more individualized notions of human functioning, practice, and training, but also of performance, improved supportive technology, and appropriate "human and technology asset management" at both individual and organization levels and over the lifespan.

Conclusions: With this, we anticipate to support the development of rehabilitation sciences and technology and to stimulate the use of rehabilitation notions in general health care. We also hope to help ensure a stronger embodiment of preventive and lifestyle medicine in rehabilitation practice. Indeed, general health care and rehabilitation practice require a healthy and active lifestyle management and research agenda in the context of primary, secondary, and tertiary prevention.IMPLICATIONS FOR REHABILITATIONContinued multidisciplinary (international) collaboration will stimulate the development of rehabilitation and human movement sciences.Notions from "human and technology asset management and ergonomics" are fundamental to rehabilitation practice and research.The rehabilitation concept will further merge into general health care and the quality there-off.
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http://dx.doi.org/10.1080/09638288.2020.1806365DOI Listing
August 2020

Short-Term Effects of a Passive Spinal Exoskeleton on Functional Performance, Discomfort and User Satisfaction in Patients with Low Back Pain.

J Occup Rehabil 2021 03;31(1):142-152

Department of Kinesiology and Physiotherapy, Faculty of Health Sciences, University of Primorska, Koper, Slovenia.

Purpose Low back pain (LBP) remains a major worldwide healthcare issue. Recently, spinal exoskeletons were proposed as a potentially useful solution for LBP prevention and vocational reintegration for people who perform heavy load lifting, repetitive movements or work in prolonged static postures. The purpose of this study was to investigate how patients with LBP respond to the novel passive SPEXOR exoskeleton regarding functional performance, discomfort and general user impression. Methods Fourteen patients, with low to moderate LBP (2-7 on a 0-10 scale), performed 12 functional tasks with and without the exoskeleton. In addition to objective performance measures, participants subjectively assessed the level of local low back discomfort, task difficulty and general discomfort on a 0-10 visual analogue scales. Results The SPEXOR exoskeleton had favourable effects on performance and local discomfort during prolonged static forward bending. Minor reductions in performance were observed for sit-stand and ladder climbing tasks. The discomfort associated with the exoskeleton was generally low to moderate (median < 4), except for the 6-min walk test (median = 4.5), which is likely due to the weight of the device and obstruction of upper limb movement. The general impressions were mostly positive, with good adjustability, low interference with the movement and moderate support reported by the participants. Conclusion The SPEXOR exoskeleton is potentially useful for LBP prevention or management, however, further improvements are needed to provide higher levels support during heavy load lifting.
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http://dx.doi.org/10.1007/s10926-020-09899-7DOI Listing
March 2021

Reliability of a battery of tests for functional evaluation of trunk exoskeletons.

Appl Ergon 2020 Jul 10;86:103117. Epub 2020 Apr 10.

University of Primorska, Faculty of Health Sciences, Department of Kinesiology and Physiotherapy, Koper, Slovenia; S2P, Science to Practice, Ltd, Laboratory for Motor Control and Motor Behaviour, Ljubljana, Slovenia. Electronic address:

Recently, several spinal exoskeletons were developed with the aim to assist occupational tasks such as load-handling and work in prolonged static postures. While the biomechanical effects of such devices has been well investigated, only limited feedback to the developers is usually provided regarding the subjective perceptions of the end-users. The aim of this study was to present a novel battery of tests, designed to assess functional performance and subjective outcomes during the use of assistive trunk exoskeletons, and to assess its test-retest reliability. The battery of tests consists of 12 different simple functional tasks. Twenty participants were included in an intra-session reliability test and repeated the tests within 7-10 days to assess inter-session reliability. They were wearing a novel passive spinal exoskeleton during all trials. The outcomes included quantitative and subjective measures, such as performance time and rating of discomfort and perceived task difficulty. The majority of the outcome measures were reliable within session and between sessions (ICC or α > 0.80). Systematic effects were observed in a few tasks, suggesting that familiarization trials will be needed to minimize the learning effects. The novel battery of tests could become an important easy-to-use tool for functional testing of the spinal exoskeletons in addition to more specific biomechanical and physiological testing. Further studies should address the reliability of the present battery of tests for assessing specific populations, such as low back pain patients and explore how to minimize systematic effects that were observed in this study.
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http://dx.doi.org/10.1016/j.apergo.2020.103117DOI Listing
July 2020

Perspectives of End Users on the Potential Use of Trunk Exoskeletons for People With Low-Back Pain: A Focus Group Study.

Hum Factors 2020 05 8;62(3):365-376. Epub 2020 Jan 8.

1190 Vrije Universiteit Amsterdam, The Netherlands.

Objective: The objective of this study was to identify criteria to be considered when developing an exoskeleton for low-back pain patients by exploring the perceptions and expectations of potential end users.

Background: Psychosocial, psychological, physical load, and personality influence incidence of low-back pain. Body-worn assistive devices that passively support the user's trunk, that is exoskeletons, can decrease mechanical loading and potentially reduce low-back pain. A user-centered approach improves patient safety and health outcomes, increases user satisfaction, and ensures usability. Still, previous studies have not taken psychological factors and the early involvement of end users into account.

Method: We conducted focus group studies with low-back pain patients ( = 4) and health care professionals ( = 8). Focus group sessions were audio-recorded, transcribed, and analyzed, using the general inductive approach. The focus group discussions included trying out an available exoskeleton. Questions were designed to elicit opinions about exoskeletons, desired design specifications, and usability.

Results: Important design characteristics were comfort, individual adjustability, independency in taking it on and off, and gradual adjustment of support. Patients raised concerns over loss of muscle strength. Health care professionals mentioned the risk of confirming disability of the user and increasing guarded movement in patients.

Conclusion: The focus groups showed that implementation of a trunk exoskeleton to reduce low-back pain requires an adequate implementation strategy, including supervision and behavioral coaching.

Application: For health care professionals, the optimal field of application, prevention or rehabilitation, is still under debate. Patients see potential in an exoskeleton to overcome their limitations and expect it to improve their quality of life.
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http://dx.doi.org/10.1177/0018720819885788DOI Listing
May 2020

The Effect of Prosthetic Alignment on Prosthetic and Total Leg Stiffness While Running With Simulated Running-Specific Prostheses.

Front Sports Act Living 2019 22;1:16. Epub 2019 Aug 22.

Department of Human Movement Sciences, Faculty of Behavioral and Movement Sciences, Vrije Universiteit Amsterdam, Amsterdam Movement Sciences, Amsterdam, Netherlands.

Running-specific prostheses (RSP) are designed to replicate the spring-like behavior of the biological leg in people with a lower limb amputation. Running performance strongly depends on stiffness of the RSP. The aim of this study was to investigate the effects of angle of alignment of the RSP on its stiffness, and how this affects total leg stiffness and the gait pattern during running. Ten able-bodied athletes performed eight trials on a treadmill with running-specific prosthetic simulators, while the alignment of the blades relative to the socket was set in four different angles (0, 5, 10, and 15°) during two different step frequency conditions (free and imposed). RSP stiffness, total leg stiffness, residual leg stiffness, and spatiotemporal parameters were measured. In both step frequency conditions, the RSP stiffness decreased linearly with increasing angle of alignment. Able bodied athletes were able to compensate for the decreased RSP stiffness, and keep total leg stiffness almost invariant, by increasing residual leg stiffness through a more straight the knee at initial contact. This study confirms that alignment is an important factor to take into account when optimizing the RSP. Whether the observed compensations are feasible in amputee athletes needs further investigation.
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http://dx.doi.org/10.3389/fspor.2019.00016DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7739705PMC
August 2019

A Comparison of the Physiology of Sedentary Behavior and Light Physical Activity in Adults With and Without a Physical Disability.

J Phys Act Health 2019 10 5;16(10):894-901. Epub 2019 Aug 5.

Background: It is questionable whether postures that are regarded as sedentary behavior in able-bodied persons evoke comparable physiological responses in adults with stroke or cerebral palsy (CP). This study aimed to compare metabolic demand and muscle activity in healthy controls, adults with stroke, and adults with CP during sedentary behavior and light physical activities.

Methods: Seventy-one adults (45.6 [18.9] y, range 18-86) participated in this study, of which there were 18 controls, 31 with stroke, and 22 with CP. The metabolic equivalent of task (MET) and level of muscle activation were assessed for different sedentary positions (sitting supported and unsupported) and light physical activities (standing and walking).

Results: During sitting supported and unsupported, people with mild to moderate stroke and CP show comparable MET and electromyographic values as controls. While sitting unsupported, people with severe stroke show higher METs and electromyographic values (P < .001), and people with severe CP only show higher METs compared with controls (P < .05) but all below 1.5 METs. Standing increased electromyographic values in people with severe stroke or CP (P < .001) and reached values above 1.5 METs.

Conclusions: Physiologic responses during sedentary behavior are comparable for controls and adults with mild to moderate stroke and CP, whereas higher metabolic demands and muscle activity (stroke only) were observed in severely affected individuals.
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http://dx.doi.org/10.1123/jpah.2019-0059DOI Listing
October 2019

Influence of arm swing on cost of transport during walking.

Biol Open 2019 Jun 10;8(6). Epub 2019 Jun 10.

Department of Human Movement Sciences, Vrije Universiteit Amsterdam, Amsterdam Movement Sciences, Amsterdam 1081 BT, The Netherlands

Normal arm swing plays a role in decreasing the cost of transport during walking. However, whether excessive arm swing can reduce the cost of transport even further is unknown. Therefore, we tested the effects of normal and exaggerated arm swing on the cost of transport in the current study. Healthy participants (=12) walked on a treadmill (1.25 m/s) in seven trials with different arm swing amplitudes (in-phase, passive restricted, active restricted, normal, three gradations of extra arm swing), while metabolic energy cost and the vertical angular momentum (VAM) and ground reaction moment (GRM) were measured. In general, VAM and GRM decreased as arm swing amplitude was increased, except for in the largest arm swing amplitude condition. The decreases in VAM and GRM were accompanied by a decrease in cost of transport from in-phase walking (negative amplitude) up to a slightly increased arm swing (non-significant difference compared to normal arm swing). The most excessive arm swings led to an increase in the cost of transport, most likely due to the cost of swinging the arms. In conclusion, increasing arm swing amplitude leads to a reduction in VAM and GRM, but it does not lead to a reduction in cost of transport for the most excessive arm swing amplitudes. Normal or slightly increased arm swing amplitude appear to be optimal in terms of cost of transport in young and healthy individuals.This article has an associated First Person interview with the first author of the paper.
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http://dx.doi.org/10.1242/bio.039263DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6602321PMC
June 2019

Cardiorespiratory fitness and physical strain during prosthetic rehabilitation after lower limb amputation.

Prosthet Orthot Int 2019 Aug 22;43(4):418-425. Epub 2019 Mar 22.

1 Department of Human Movement Sciences, Faculty of Behavioural and Movement Sciences, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands.

Background: Sufficient cardiorespiratory fitness has been regarded a prerequisite for prosthetic walking. In order to improve cardiorespiratory fitness, adequate strain ought to be placed on the system during training.

Objectives: To determine cardiorespiratory fitness at the start and end of inpatient rehabilitation after lower limb amputation and determine the physical strain experienced during conventional prosthetic rehabilitation.

Study Design: Multicenter prospective cohort study.

Methods: Cardiorespiratory fitness was assessed using a peak one-legged cycle exercise test. Physical strain was assessed during a minimum of three full rehabilitation days using heart rate recordings. Physical strain was expressed in the time per day that heart rate exceeded 40% of heart rate reserve.

Results: At the start of rehabilitation, peak aerobic capacity was on average 16.9 (SD, 6.5) mL/kg/min ( = 33). Overall, peak aerobic capacity did not improve over the course of rehabilitation ( = 23,  = 0.464). Fifty percent of the patients experienced a physical strain level that satisfies minimum criteria for maintaining cardiorespiratory fitness (>40% heart rate reserve for 30 min/day).

Conclusion: Cardiorespiratory fitness was low and did not increase during conventional prosthetic rehabilitation. On average, the physical strain during rehabilitation was insufficient to elicit potential improvements in aerobic capacity. Results stress the need for dedicated physical training modules at the individual level.

Clinical Relevance: This study shows that clinicians ought to be aware of the relatively low cardiorespiratory fitness of people who have undergone lower limb amputation and that improvements during rehabilitation are not always obtained. Results stress the need for physical training modules in which intensity is imposed at the individual level.
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http://dx.doi.org/10.1177/0309364619838084DOI Listing
August 2019

Validation of the stabilometer balance test: Bridging the gap between clinical and research based balance control assessments for stroke patients.

Gait Posture 2019 01 29;67:77-84. Epub 2018 Sep 29.

Research and Development, Heliomare Rehabilitation Center, Relweg 51, 1949 EC, Wijk aan Zee, the Netherlands; Department of Human Movement Sciences, Faculty of Behavioural and Movement Sciences, Vrije Universiteit, De Boelelaan 1105, 1081 HV, Amsterdam, the Netherlands.

Background: A pronounced discrepancy exists between balance assessments for stroke survivors that are used for clinical purposes and those used for research. Clinical assessments like the Berg Balance Scale generally have stronger ecological validity, whereas research-based assessments like posturography are generally more reliable and precise. We developed a stabilometer balance test (SBT) that aims to couple measurement reliability and precision to clinical meaningfulness by means of a personalized and adaptive test procedure.

Research Question: To examine the validity, reliability, and measurement error of the stabilometer balance test in inpatient stroke patients.

Methods: In this cross-sectional study, inpatient stroke patients (FAC > 2) were tested on a stabilometer with adjustable resistance to mediolateral movement. A modified staircase procedure was used to adapt task difficulty (i.e., rotational stiffness) on a trial-by-trial basis. The main outcome was the threshold stiffness at which a patient could just stay balanced. Threshold stiffness was correlated with the Berg Balance Scale and posturography measurements to determine concurrent validity (N = 86). Test-retest reliability (N = 23) was analyzed with the Intraclass Correlation Coefficient (ICC). Floor and ceiling effects were assessed. The minimal detectable change was determined at individual and group level.

Results: Threshold rotational stiffness moderately correlated with the Berg Balance Scale (r=-0.559, p < 0.001), and the absolute path length of the center of pressure during posturography (r=0.348, p = 0.006). Test-retest reliability was good to excellent (ICC=0.869; 95%CI=0.696-0.944). There were no floor or ceiling effects. The minimal detectable change was sufficiently small to detect relevant changes in balance control both on individual and group level.

Relevance: The SBT is both a valid and reliable balance assessment in stroke patients. It is at least as precise as current clinically preferred measures and does not suffer from ceiling effects. Therefore, it is suitable for use in clinical practice as well as research.
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http://dx.doi.org/10.1016/j.gaitpost.2018.09.025DOI Listing
January 2019

Energy storing and return prosthetic feet improve step length symmetry while preserving margins of stability in persons with transtibial amputation.

J Neuroeng Rehabil 2018 09 5;15(Suppl 1):76. Epub 2018 Sep 5.

Production Directorate, Applied Research, INAIL Prosthesis Center, Vigorso di Budrio, Bologna, Italy.

Background: Energy storing and return (ESAR) feet are generally preferred over solid ankle cushioned heel (SACH) feet by people with a lower limb amputation. While ESAR feet have been shown to have only limited effect on gait economy, other functional benefits should account for this preference. A simple biomechanical model suggests that enhanced gait stability and gait symmetry could prove to explain part of the difference in the subjective preference between both feet.

Aim: To investigate whether increased push-off power with ESAR feet increases center of mass velocity at push off and enhance intact step length and step length symmetry while preserving the margin of stability during walking in people with a transtibial prosthesis.

Methods: Fifteen people with a unilateral transtibial amputation walked with their prescribed ESAR foot and a SACH foot at a fixed walking speed (1.2 m/s) over a level walkway while kinematic and kinetic data were collected. Push-off work generated by the foot, center of mass velocity, step length, step length symmetry and backward margin of stability were assessed and compared between feet.

Results: Push-off work was significantly higher when using the ESAR foot compared to the SACH foot. Simultaneously, center of mass velocity at toe-off was higher with ESAR compared to SACH, and intact step length and step length symmetry increased without reducing the backward margin of stability.

Conclusion: Compared to the SACH foot, the ESAR foot allowed an improvement of step length symmetry while preserving the backward margin of stability at community ambulation speed. These benefits may possibly contribute to the subjective preference for ESAR feet in people with a lower limb amputation.
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http://dx.doi.org/10.1186/s12984-018-0404-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6157252PMC
September 2018

Are the effects of internal focus instructions different from external focus instructions given during balance training in stroke patients? A double-blind randomized controlled trial.

Clin Rehabil 2019 Feb 31;33(2):207-221. Epub 2018 Aug 31.

3 Clinical Neuropsychology Section, Faculty of Behavioural and Movement Sciences, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands.

Objective:: This study aimed to assess if external focus instructions result in greater improvements in motor skill and automaticity compared to internal focus instructions in stroke patients.

Design:: Double-blind randomized controlled trial.

Setting:: Inpatient stroke rehabilitation unit.

Subjects:: A total of 63 stroke patients (Mean = 59.6 ± 10.7 years; Mean = 28.5 ± 16.6; Median = 4).

Interventions:: Patients were randomly assigned to an internal ( N = 31) or external ( N = 32) focus instruction group. Both groups practiced a balance board stabilization task, three times per week, for three weeks. Balance performance was assessed at baseline, and after one and three weeks of practice.

Main Measures:: Primary outcome was the threshold stiffness (Nm/rad) at which patients could stay balanced. Secondary outcomes were patients' sway (root-mean-square error in degrees) at the baseline threshold stiffness under single- and dual-task conditions, and their performance on the Timed Up and Go Test and Utrecht Scale for Evaluation of Rehabilitation.

Results:: Both groups achieved similar improvements in threshold stiffness (∆= 27.1 ± 21.1 Nm/rad), and single- (∆= 1.8 ± 2.3° root-mean-square error) and dual-task sway (∆= 1.7 ± 2.1° root-mean-square error) after three weeks of practice. No differences were found in improvements in clinical tests of balance and mobility. Patients with comparatively good balance and sensory function, and low attention capacity showed greatest improvements with external focus instructions.

Conclusion:: External focus instructions did not result in greater improvement in balance skill in stroke patients compared to internal focus instructions. Results suggest that tailoring instructions to the individual stroke patient may result in optimal improvements in motor skill.
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http://dx.doi.org/10.1177/0269215518795243DOI Listing
February 2019

Lower limb muscle fatigue during walking in children with cerebral palsy.

Dev Med Child Neurol 2019 02 29;61(2):212-218. Epub 2018 Aug 29.

Department of Neuromedicine and Movement Science, Norwegian University of Science and Technology, Trondheim, Norway.

Aim: To investigate whether more prominent signs of muscle fatigue occur during self-paced walking in children with cerebral palsy (CP) compared to typically developing peers.

Method: In this case-control study, 13 children with CP (four males, nine females; mean age [SD] 11y 4mo [3y 8mo]; nine in Gross Motor Function Classification System [GMFCS] level I, three in GMFCS level II, and one in GMFCS level III) and 14 typically developing peers (nine males, five females; mean age [SD] 9y 10mo [1y 10mo]) walked 5 minutes overground at a self-selected walking speed. Electromyography (EMG) median frequency and root mean square (RMS) were identified per gait cycle from EMG recordings of the tibialis anterior, gastrocnemius medialis, soleus, rectus femoris, and semitendinosus. Rate of change in those variables was analysed using mixed linear model analyses.

Results: The decrease in EMG median frequency of gastrocnemius medialis and soleus and increase in EMG-RMS of tibialis anterior, gastrocnemius medialis, and soleus were significantly larger in the most affected leg of children with CP compared with typically developing peers.

Interpretation: Increased selective muscle fatigue of the lower leg muscles was observed during self-paced walking in children with mild-to-moderate severe CP. This could contribute to and account for limited walking capacity.

What This Paper Adds: Children with cerebral palsy (CP) show more signs of lower leg muscle fatigue than typically developing peers. No signs of muscle fatigue were observed in upper leg muscles of children with CP.
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http://dx.doi.org/10.1111/dmcn.14002DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7379556PMC
February 2019

How physical therapists instruct patients with stroke: an observational study on attentional focus during gait rehabilitation after stroke.

Disabil Rehabil 2018 May 24;40(10):1154-1165. Epub 2017 Feb 24.

b Department of Clinical Neuropsychology, Faculty of Behavioural and Movement Sciences , VU University Amsterdam , Amsterdam , The Netherlands.

Purpose: People without neurological impairments show superior motor learning when they focus on movement effects (external focus) rather than on movement execution itself (internal focus). Despite its potential for neurorehabilitation, it remains unclear to what extent external focus strategies are currently incorporated in rehabilitation post-stroke. Therefore, we observed how physical therapists use attentional focus when treating gait of rehabilitating patients with stroke.

Methods: Twenty physical therapist-patient couples from six rehabilitation centers participated. Per couple, one regular gait-training session was video-recorded. Therapists' statements were classified using a standardized scoring method to determine the relative proportion of internally and externally focused instructions/feedback. Also, we explored associations between therapists' use of external/internal focus strategies and patients' focus preference, length of stay, mobility, and cognition.

Results: Therapists' instructions were generally more external while feedback was more internal. Therapists used relatively more externally focused statements for patients with a longer length of stay (B = -0.239, p = 0.013) and for patients who had a stronger internal focus preference (B = -0.930, p = 0.035).

Conclusions: Physical therapists used more external focus instructions, but more internally focused feedback. Also, they seem to adapt their attentional focus use to patients' focus preference and rehabilitation phase. Future research may determine how these factors influence the effectiveness of different attentional foci for motor learning post-stroke. IMPLICATIONS FOR REHABILITATION Physical therapists use a balanced mix of internal focus and external focus instructions and feedback when treating gait of stroke patients. Therapists predominantly used an external focus for patients in later rehabilitation phases, and for patients with stronger internal focus preferences, possibly in an attempt to stimulate more automatic control of movement in these patients. Future research should further explore how a patients' focus preference and rehabilitation phase influence the effectiveness of different focus strategies. Awaiting further research, we recommend that therapists use both attentional focus strategies, and explore per patient which focus works best on a trial-and-error basis.
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http://dx.doi.org/10.1080/09638288.2017.1290697DOI Listing
May 2018

Regulation of step frequency in transtibial amputee endurance athletes using a running-specific prosthesis.

J Biomech 2017 01 29;51:42-48. Epub 2016 Nov 29.

Department of Human Movement Sciences, Faculty of Behaviour and Movement Sciences, Vrije Universiteit Amsterdam, MOVE Research Institute Amsterdam, The Netherlands; Heliomare Research and Development, Wijk aan Zee, The Netherlands.

Running specific prostheses (RSP) are designed to replicate the spring-like behaviour of the human leg during running, by incorporating a real physical spring in the prosthesis. Leg stiffness is an important parameter in running as it is strongly related to step frequency and running economy. To be able to select a prosthesis that contributes to the required leg stiffness of the athlete, it needs to be known to what extent the behaviour of the prosthetic leg during running is dominated by the stiffness of the prosthesis or whether it can be regulated by adaptations of the residual joints. The aim of this study was to investigate whether and how athletes with an RSP could regulate leg stiffness during distance running at different step frequencies. Seven endurance runners with an unilateral transtibial amputation performed five running trials on a treadmill at a fixed speed, while different step frequencies were imposed (preferred step frequency (PSF) and -15%, -7.5%, +7.5% and +15% of PSF). Among others, step time, ground contact time, flight time, leg stiffness and joint kinetics were measured for both legs. In the intact leg, increasing step frequency was accompanied by a decrease in both contact and flight time, while in the prosthetic leg contact time remained constant and only flight time decreased. In accordance, leg stiffness increased in the intact leg, but not in the prosthetic leg. Although a substantial contribution of the residual leg to total leg stiffness was observed, this contribution did not change considerably with changing step frequency. Amputee athletes do not seem to be able to alter prosthetic leg stiffness to regulate step frequency during running. This invariant behaviour indicates that RSP stiffness has a large effect on total leg stiffness and therefore can have an important influence on running performance. Nevertheless, since prosthetic leg stiffness was considerably lower than stiffness of the RSP, compliance of the residual leg should not be ignored when selecting RSP stiffness.
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http://dx.doi.org/10.1016/j.jbiomech.2016.11.058DOI Listing
January 2017

Disability and rehabilitation on the move: mobility, exercise and sports for people with physical disabilities.

Disabil Rehabil 2017 01 6;39(2):113-114. Epub 2016 Sep 6.

a Department of Human Movement Sciences , Faculty of Behaviour and Movement Sciences, Vrije Universiteit Amsterdam, MOVE Research Institute Amsterdam , Amsterdam , The Netherlands.

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http://dx.doi.org/10.1080/09638288.2016.1217079DOI Listing
January 2017

Coactivation During Dynamometry Testing in Adolescents With Spastic Cerebral Palsy.

Phys Ther 2016 09 25;96(9):1438-47. Epub 2016 Feb 25.

H. Houdijk, PhD, Research and Development, Heliomare Rehabilitation; Human Movement Sciences, Faculty of Behaviour and Movement Sciences, Vrije Universiteit Amsterdam; and MOVE Research Institute Amsterdam, Amsterdam, the Netherlands.

Background: Dynamometry has been used extensively to measure knee extensor strength in individuals with cerebral palsy (CP). However, increased coactivation can lead to underestimation of knee extensor strength and, therefore, reduce validity of strength measurements. It is yet unknown to what extent coactivation occurs during dynamometry testing and whether coactivation is influenced by severity of CP, load levels, and muscle fatigue.

Objectives: The aims of this study were: (1) to investigate coactivation in adolescents with and without CP during dynamometer tests and (2) to assess the effect of Gross Motor Function Classification System (GMFCS) level, load level, and muscle fatigue on coactivation.

Design: A cross-sectional observational design was used.

Method: Sixteen adolescents with CP (GMFCS levels I and II: n=10/6; age range=13-19 years) and 15 adolescents without CP (n=15; age range=12-19 years) performed maximal isometric contractions (maximal voluntary torque [MVT]) and a series of submaximal dynamic contractions at low (±65% MVT), medium (±75% MVT), and high (±85% MVT) loads until fatigue. A coactivation index (CAI) was calculated for each contraction from surface electromyography recordings from the quadriceps and hamstring muscles.

Results: Adolescents with CP classified in GMFCS level II showed significantly higher CAI values than adolescents classified in GMFCS level I and those without CP during maximal and submaximal contractions. No differences were observed among load levels. During the series of fatiguing submaximal contractions, CAI remained constant in both the CP group and the group with typical development (TD), except for adolescents with TD at the low-load condition, which showed a significant decrease.

Limitations: Electromyography tracings were normalized to amplitudes during maximal isometric contractions, whereas previous studies suggested that these types of contractions could not be reliably determined in the CP population.

Conclusion: Coactivation was higher in adolescents with CP classified in GMFCS level II than in adolescents with TD and those with CP in GMFCS level I at different load levels. Within all groups, coactivation was independent of load level and fatigue. In individuals with CP, coactivation can lead to an underestimation of agonist muscle strength, which should be taken into account while interpreting the results of both maximal and submaximal dynamometer tests.
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http://dx.doi.org/10.2522/ptj.20140448DOI Listing
September 2016

Relations between muscle endurance and subjectively reported fatigue, walking capacity, and participation in mildly affected adolescents with cerebral palsy.

Dev Med Child Neurol 2016 08 24;58(8):814-21. Epub 2016 Feb 24.

Department of Rehabilitation Medicine, MOVE Research Institute Amsterdam, VU University Medical Center, Amsterdam, the Netherlands.

Aim: To investigate the relation between muscle endurance and subjectively reported fatigue, walking capacity, and participation in mildly affected adolescents with cerebral palsy (CP) and peers with typical development.

Method: In this case-control study, knee extensor muscle endurance was estimated from individual load-endurance curves as the load corresponding to a 15-repetition maximum in 17 adolescents with spastic CP (six males, 11 females; age 12-19y) and 18 adolescents with typical development (eight males, 10 females; age 13-19y). Questionnaires were used to assess subjectively reported fatigue (Pediatric Quality of Life Inventory Multidimensional Fatigue Scale) and participation (Life-Habits questionnaire). Walking capacity was assessed using the 6-minute walk test. Relations were determined using multiple regression analyses.

Results: Muscle endurance related significantly to subjectively reported fatigue and walking capacity in adolescents with CP, while no relations were found for adolescents with typical development (subjectively reported fatigue: regression coefficient β [95% confidence intervals] for CP=23.72 [6.26 to 41.18], for controls=2.72 [-10.26 to 15.69]; walking capacity β for CP=125m [-87 to 337], for controls=2m [-86 to 89]). The 15-repetition maximum did not relate to participation in adolescents with CP.

Interpretation: Subjectively reported fatigue and reduced walking capacity in adolescents with CP are partly caused by lower muscle endurance of knee extensors. Training of muscle endurance might contribute to reducing the experience of fatigue and improving walking capacity. Reduced muscle endurance seems to have no effect on participation.
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http://dx.doi.org/10.1111/dmcn.13083DOI Listing
August 2016

An Incremental Shuttle Wheel Test for Wheelchair Tennis Players.

Int J Sports Physiol Perform 2016 Nov 24;11(8):1111-1114. Epub 2016 Aug 24.

Purpose: To determine the relationship between outcomes of the shuttle wheel test (SWT) and peak oxygen uptake (VOpeak) during that test and whether SWT and VOpeak can discriminate between different skill levels of wheelchair tennis players.

Methods: Fifteen wheelchair tennis players performed an SWT on a tennis court while VO was measured continuously. Outcome measures were VOpeak and achieved stage. Relations between outcomes and Dutch wheelchair tennis ranking were calculated with Spearman correlation. Independent t tests were used to test for differences between national and international players.

Results: Moderate correlations were found between VO2peak and SWT outcome (r = .40-.47). The tennis ranking correlated weakly with VOpeak (r = -.35) and strongly with SWT outcome (r = -.80). A significant difference was found between national and international players for achieved stage (P = .027) and VOpeak (P = .027).

Conclusions: The SWT outcome only explained a small part of the variance in VOpeak among players, so it cannot be considered a valid test for aerobic capacity. However, SWT outcomes are related to the skill level of the player and give a good indication of the overall peak wheelchair performance.
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http://dx.doi.org/10.1123/ijspp.2015-0598DOI Listing
November 2016

Isometric muscle strength and mobility capacity in children with cerebral palsy.

Disabil Rehabil 2017 01 25;39(2):135-142. Epub 2015 Nov 25.

a Department of Rehabilitation Medicine , EMGO Institute for Health and Care Research and MOVE Research Institute, VU University Medical Center , Amsterdam , The Netherlands.

Purpose: To determine the relationship between isometric leg muscle strength and mobility capacity in children with cerebral palsy (CP) compared to typically developing (TD) peers.

Method: Participants were 62 children with CP (6-13 years), able to walk with (n = 10) or without (n = 52) walking aids, and 47 TD children. Isometric muscle strength of five muscle groups of the leg was measured using hand-held dynamometry. Mobility capacity was assessed with the 1-min walk, the 10-m walk, sit-to-stand, lateral-step-up and timed-stair tests.

Results: Isometric strength of children with CP was reduced to 36-82% of TD. When adjusted for age and height, the percentage of variance in mobility capacity that was explained by isometric strength of the leg muscles was 21-24% (walking speed), 25% (sit-to-stand), 28% (lateral-step-up) and 35% (timed-stair) in children with CP. Hip abductors and knee flexors had the largest contribution to the explained variance, while knee extensors showed the weakest correlation. Weak or no associations were found between strength and mobility capacity in TD children.

Conclusion: Isometric strength, especially hip abductor and knee flexor strength, is moderately related to mobility capacity in children with CP, but not in TD children. To what extent training of these muscle groups will lead to better mobility capacity needs further study. Implications for Rehabilitation Strength training in children with cerebral palsy (CP) may be targeted more specifically at hip abductors and knee flexors. The moderate associations imply that large improvements in mobility capacity may not be expected when strength increases.
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http://dx.doi.org/10.3109/09638288.2015.1095950DOI Listing
January 2017

Hind- and Midfoot Motion After Ankle Arthrodesis.

Foot Ankle Int 2015 Dec 9;36(12):1430-7. Epub 2015 Jul 9.

Academic Medical Center Amsterdam, Amsterdam, The Netherlands.

Background: After ankle arthrodesis (AA), compensatory increased range of motion in adjacent joints might lead to increased osteoarthritis. Evaluation of patient-reported outcomes after AA with validated questionnaires is rare. Likewise, reliable radiographic analysis of the position of the AA, expected to influence the range of motion of the hind- and midfoot, is lacking. Therefore, the current study was performed.

Methods: Seventeen patients with unilateral AA were included. Sagittal hind- and midfoot range of motion was measured radiographically. The position of the AA in the sagittal and coronal planes and osteoarthritis of adjacent joints were also evaluated radiographically. Measurements were compared to the contralateral side. Patient-reported outcomes via validated questionnaires were compared to a control group (n = 18).

Results: Average follow-up was 3.5 years. Mean combined hind- and midfoot sagittal range of motion after AA equaled that of the contralateral side (20.8 vs. 21.0 degrees; P = .93). The tibiotalar angle after AA equaled that of the contralateral side (107 vs. 107 degrees; P = .86). The talus was translated posteriorly after AA (T-T ratio 0.45 vs. 0.34; P < .001). Low intraclass correlation coefficients (ICC) precluded reliable evaluation of the coronal position of the hindfoot (ICC, 0.07 and -0.34) and osteoarthritis in adjacent joints (ICC range, 0-0.54). SF-36 physical health scores after AA are lower as compared with those of controls (50 vs. 56; P = .01). Scores on the Foot and Ankle Outcome Score and Ankle Osteoarthritis Scale were also significantly lower. Patient satisfaction with AA was high (average visual analog scale score, 83).

Conclusion: No increased sagittal range of motion in the hind- and midfoot after AA was found at 3.5 years of follow-up as compared with the contralateral side. Tibiotalar angles were equal. The talus was translated posteriorly. The hindfoot alignment view was not suitable to analyze the position of the hindfoot. Low ICC of the Kellgren and Lawrence scale precluded evaluation of osteoarthritis of adjacent joints. Patients scored lower than controls on self-reported outcome questionnaires but were satisfied with the result of AA.
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http://dx.doi.org/10.1177/1071100715593913DOI Listing
December 2015

Relation between postural sway magnitude and metabolic energy cost during upright standing on a compliant surface.

J Appl Physiol (1985) 2015 Sep 9;119(6):696-703. Epub 2015 Jul 9.

Faculty of Human Movement Sciences, MOVE Research Institute Amsterdam, VU University Amsterdam, Amsterdam, The Netherlands; and.

Postural control performance is often described in terms of postural sway magnitude, assuming that lower sway magnitude reflects better performance. However, people do not typically minimize sway magnitude when performing a postural control task. Possibly, other criteria are satisfied when people select the amount of sway they do. Minimal metabolic cost has been suggested as such a criterion. The aim of this study was to experimentally test the relation between sway magnitude and metabolic cost to establish whether metabolic cost could be a potential optimization criterion in postural control. Nineteen healthy subjects engaged in two experiments in which different magnitudes of sway were evoked during upright standing on a foam surface while metabolic energy expenditure, center of pressure (CoP) excursion, and muscle activation were recorded. In one experiment, sway was manipulated by visual feedback of CoP excursion. The other experiment involved verbal instructions of standing still, natural or relaxed. In both experiments, metabolic cost changed with sway magnitude in an asymmetric parabolic fashion, with a minimum around self-selected sway magnitudes and a larger increase at small compared with large sway magnitudes. This metabolic response was paralleled by a change in tonic and phasic EMG activity in the major leg muscles. It is concluded that these results are in line with the notion that metabolic cost can be an optimization criterion used to set postural control and as such could account for the magnitude of naturally occurring postural sway in healthy individuals, although the pathway remains to be elucidated.
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http://dx.doi.org/10.1152/japplphysiol.00907.2014DOI Listing
September 2015
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