Publications by authors named "Tine Alkjaer"

72 Publications

Reference data for hop tests used in pediatric ACL injury rehabilitation: A cross-sectional study of healthy children.

Scand J Med Sci Sports 2021 Sep 22;31(9):1832-1839. Epub 2021 May 22.

Department of Midwifery, Physiotherapy, Occupational Therapy and Psychomotor Therapy, Faculty of Health, University College Copenhagen, Copenhagen, Denmark.

In rehabilitation, four single-leg hop tests are frequently used for evaluation of ACL-injured children. However, reference values on single-leg hop performance and the corresponding limb symmetry indexes (LSIs) of healthy children younger than 15 years of age are lacking. Thus, the purpose was to describe hop performance and LSIs in healthy Danish children, and to quantify the proportion of participants passing LSI values of ≥85% as well as ≥90%. Healthy children aged 9-15 years were invited to participate in the study. Hop performance (single hop, 6-m timed hop, triple hop, and cross-over hop) was assessed for each leg for each hop test and expressed as absolute, normalized (to body height), and LSI values. Descriptive statistics were applied to calculate mean ±SD for all outcomes within age and gender groups. Further, the 95% reference interval was calculated for each age and gender group. A total of 531 healthy children (52% girls) were included in the study, representing seven age groups (9-15 years). The LSI group means across all participants for the four hop tests ranged between 84 and 95%. Between 70 and 83% of the children had an LSI of ≥85%, while 50 to 65% of the children had an LSI of ≥90%. The present reference material can be used in clinical practice when evaluating hop performance in pediatric ACL patients.
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http://dx.doi.org/10.1111/sms.13986DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8453553PMC
September 2021

Influence of Wearing Ballistic Vests on Physical Performance of Danish Police Officers: A Cross-Over Study.

Sensors (Basel) 2021 Mar 5;21(5). Epub 2021 Mar 5.

National Research Centre for Working Environment, 2100 Copenhagen Ø, Denmark.

Purpose: We aimed to investigate the influence of wearing a ballistic vest on physical performance in police officers.

Methods: We performed a cross-over study to investigate the influence of wearing a ballistic vest on reaction and response time, lumbar muscle endurance and police vehicle entry and exit times. Reaction and response time was based on a perturbation setup where the officers' pelvises were fixed and EMG of lumbar and abdominal muscles was recorded. We used a modified Biering-Sørensen test to assess the lumbar muscle endurance and measured duration of entry and exit maneuvers in a variety of standard-issue police cars.

Results: There was a significant difference of 24% in the lumbar muscle endurance test (no vest: 151 s vs. vest: 117 s), and the police officers experienced higher physical fatigue after the test when wearing a vest. Furthermore, officers took longer to both enter and exit police cars when wearing a vest (range: 0.24-0.56 s) depending on the model of the vehicle. There were no significant differences in reaction and response times between the test conditions (with/without vest).

Discussion And Conclusion: Wearing of a ballistic vest significantly influenced the speed of movement in entry and exit of police cars and lumbar muscle endurance, although it does not seem to affect reaction or response times. The ballistic vest seems to impair performance of tasks that require maximal effort, which calls for better designs of such vests.
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http://dx.doi.org/10.3390/s21051795DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7961692PMC
March 2021

The influence of an orthopaedic walker boot on forefoot force.

Foot (Edinb) 2021 Mar 10;46:101739. Epub 2020 Sep 10.

Institute of Sports Medicine Copenhagen, Bispebjerg and Frederiksberg Hospital, Nielsine Nielsens Vej 11, 2400 Copenhagen NV, Denmark; Department of Physical and Occupational Therapy, Bispebjerg and Frederiksberg Hospital, Nielsine Nielsens Vej 10, 2400 Copenhagen NV, Denmark.

Background: In the treatment of an Achilles tendon rupture the patients are commonly equipped with an orthopaedic walker boot with wedges. To what extent this influences the tensile force placed on the Achilles tendon is unclear.

Purpose: To assess the forefoot force and describe changes in muscle activity of the medial gastrocnemius, soleus and tibialis anterior when using one or three wedges during ambulation in a weightbearing orthopaedic walker boot.

Methods: The force on the forefoot was measured with a force sensor insole and muscle activity of the medial gastrocnemius, soleus and tibialis anterior were measured using surface electromyography in 10 healthy participants. Three different types of ambulation were performed (walking without crutches (unass.), walking with crutches (+crutch) and walking with crutches and verbal instructions to place body weight on heel (heel+crutch) with one and three heel wedges respectively.

Findings: The total peak force displayed an interaction where forefoot force decreased when wearing three wedges only for the +crutch ambulation type (80N, p=0.001) although there was a trend to decrease with three wedges also for the heel+crutch ambulation type (48N, p=0.05). The relative peak force on the forefoot showed a main effect with a significant decrease when using three wedges compared to one wedge across all three ambulation types (19.1%, p=0.009).

Interpretation: The force on the forefoot and hereby the Achilles tendon significantly decreased when using three wedges compared to one wedge. These findings have important implications for the rehabilitation post Achilles tendon rupture.
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http://dx.doi.org/10.1016/j.foot.2020.101739DOI Listing
March 2021

Functional muscle synergies to support the knee against moment specific loads while weight bearing.

J Electromyogr Kinesiol 2021 Feb 21;56:102506. Epub 2020 Nov 21.

School of Rehabilitation Sciences, University of Ottawa, 451 Smyth Rd, Ottawa, ON K1H 8M5, Canada; School of Human Kinetics, University of Ottawa, 125 University Pr, Ottawa, ON K1N 1A2, Canada. Electronic address:

Objective: Externally applied abduction and rotational loads are major contributors to the knee joint injury mechanism; yet, how muscles work together to stabilize the knee against these loads remains unclear. Our study sought to evaluate lower limb functional muscle synergies in healthy young adults such that muscle activation can be directly related to internal knee joint moments.

Methods: Concatenated non-negative matrix factorization extracted muscle and moment synergies of 22 participants from electromyographic signals and joint moments elicited during a weight-bearing force matching protocol.

Results: Two synergy sets were extracted: Set 1 included four synergies, each corresponding to a general anterior, posterior, medial, or lateral force direction. Frontal and transverse moments were coupled during medial and lateral force directions. Set 2 included six synergies, each corresponding to a moment type (extension/flexion, ab/adduction, internal/external rotation). Hamstrings and quadriceps dominated synergies associated with respective flexion and extension moments while quadriceps-hamstring co-activation was associated with knee abduction. Rotation moments were associated with notable contributions from hamstrings, quadriceps, gastrocnemius, and hip ab/adductors, corresponding to a general co-activation muscle synergy.

Conclusion: Our results highlight the importance of muscular co-activation of all muscles crossing the knee to support it during injury-inducing loading conditions such as externally applied knee abduction and rotation. Functional muscle synergies can provide new insight into the relationship between neuromuscular control and knee joint stability by directly associating biomechanical variables to muscle activation.
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http://dx.doi.org/10.1016/j.jelekin.2020.102506DOI Listing
February 2021

Effect of footwear on intramuscular EMG activity of plantar flexor muscles in walking.

J Electromyogr Kinesiol 2020 Dec 18;55:102474. Epub 2020 Sep 18.

Neuromuscular Research Centre, Faculty of Sport and Health Sciences, University of Jyvaskyla, Finland; Department for Health, Bath University, UK.

One of the purposes of footwear is to assist locomotion, but some footwear types seem to restrict natural foot motion, which may affect the contribution of ankle plantar flexor muscles to propulsion. This study examined the effects of different footwear conditions on the activity of ankle plantar flexors during walking. Ten healthy habitually shod individuals walked overground in shoes, barefoot and in flip-flops while fine-wire electromyography (EMG) activity was recorded from flexor hallucis longus (FHL), soleus (SOL), and medial and lateral gastrocnemius (MG and LG) muscles. EMG signals were peak-normalised and analysed in the stance phase using Statistical Parametric Mapping (SPM). We found highly individual EMG patterns. Although walking with shoes required higher muscle activity for propulsion than walking barefoot or with flip-flops in most participants, this did not result in statistically significant differences in EMG amplitude between footwear conditions in any muscle (p > 0.05). Time to peak activity showed the lowest coefficient of variation in shod walking (3.5, 7.0, 8.0 and 3.4 for FHL, SOL, MG and LG, respectively). Future studies should clarify the sources and consequences of individual EMG responses to different footwear.
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http://dx.doi.org/10.1016/j.jelekin.2020.102474DOI Listing
December 2020

Evaluation of abdominal exercises after stoma surgery: a descriptive study.

Disabil Rehabil 2020 Jun 8:1-10. Epub 2020 Jun 8.

Department of Physiotherapy and Occupational Therapy, Copenhagen University Hospital, Herlev and Gentofte, Copenhagen, Denmark.

To evaluate the feasibility of exercises for the abdominal muscles in patients after colostomy or ileostomy formation on the following parameters: muscle activity, pain, discomfort, and difficulty of performing the exercises. Patients with a new stoma were divided into groups based on time after surgery: Early group, 0-2 weeks ( = 12); Intermediate group, 2-6 weeks ( = 15); and Late group, 6-12 weeks ( = 10). During a single individual test session, participants in each group performed a different set of 10-11 abdominal coordination and strengthening exercises for the abdominal muscles. Activity of the abdominal muscles was measured with electromyography. Pain, discomfort, and difficulty were rated for each exercise. For the Early group, muscle activity reaching a predetermined threshold was measured for half of the participants in a few exercises. In both the Intermediate group and the Late group, muscle activity reaching the onset criteria was measured for all muscles for a high percentage of participants in several exercises. Both strengthening and coordinating exercises were feasible based on low ratings of pain, discomfort, and difficulty. This study identified feasible exercises that activated the abdominal muscles at different time points after stoma formation. The observations can be used as guidance for the choice of exercises in clinical practice and future research.Implications for rehabilitationThe findings of this study can be used in clinical practice as guidance for choice of exercise at different time points after surgery.This study identified useful exercises for activating the abdominal muscles in rehabilitation after stoma surgery from two weeks on.In the first two postoperative weeks, there was limited involvement of the abdominal muscles with the evaluated exercises.Most of the evaluated abdominal exercises were feasible after stoma surgery based on pain, discomfort, and difficulty.
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http://dx.doi.org/10.1080/09638288.2020.1771620DOI Listing
June 2020

Dynamics of Postural Control in Elite Sport Rifle Shooters.

J Mot Behav 2021 11;53(1):20-29. Epub 2020 Feb 11.

Department of Biomedical Sciences, University of Copenhagen, Copenhagen N, Denmark.

Thirteen shooters and eleven non-shooters completed two-legged and single-legged stance on a force platform. The dynamics of the center of pressure trajectory was assessed using sample entropy, correlation dimension and entropic half-life. Additionally, the body sway was quantified as the elliptical area of the trajectory. The shooters had lower sample entropy and tended to have longer entropic half-life during the single-legged stance. Across the two tasks, the correlation dimension in the anterior-posterior direction and the body sway in both directions were lower in the shooters. This suggests that extensive training in quiet stance is associated with altered postural control, especially during challenging single-legged stance and to a lesser extend during two-legged stance.
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http://dx.doi.org/10.1080/00222895.2020.1723478DOI Listing
June 2021

Wearable electromyography recordings during daily life activities in children with cerebral palsy.

Dev Med Child Neurol 2020 06 27;62(6):714-722. Epub 2020 Jan 27.

Department of Neuroscience, University of Copenhagen, Copenhagen, Denmark.

Aim: To test whether wearable textile electromyography (EMG) recording systems may detect differences in muscle activity levels during daily activities between children with cerebral palsy (CP) and age-matched typically developing children.

Method: Wearable textile EMG recording systems were used to obtain leg muscle activity in 10 children with spastic CP (four females, six males; mean age 9y 6mo, standard deviation [SD] 2y 4mo, range: 6-13y; Gross Motor Function Classification System [GMFCS] level I and II) and 11 typically developing children (four females, seven males; mean age 9y 9mo, SD 1y 11mo, 7-12y) at rest and while performing seven daily activities.

Results: Children with CP showed significantly lower absolute EMG levels during maximal voluntary contractions (MVCs) of muscles on the most affected side as compared to the least affected side and to typically developing children. None of the typically developing children or children with CP showed detectable EMG activity in resting situations. EMG activity relative to MVC was greater in children with CP during walking, jumping, and kicking on the most affected side as compared to the least affected side and to typically developing children.

Interpretation: Wearable textile EMG recording systems may be used to determine differences in muscle activity during daily activities in children with CP. Children with CP showed reduced muscle activity during daily activities compared to their peers, but used a significantly larger part of their maximal voluntary muscle strength to perform these activities.

What This Paper Adds: Wearable textile electromyography (EMG) systems are feasible for measurement of daily muscle activity in children with cerebral palsy (CP). Children with CP showed reduced EMG levels during maximal voluntary contractions. Neither typically developing children or children with CP showed EMG activity in resting situations. Children with CP used a larger part of their voluntary muscle strength during daily activities.
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http://dx.doi.org/10.1111/dmcn.14466DOI Listing
June 2020

Forward lunge before and after anterior cruciate ligament reconstruction: Faster movement but unchanged knee joint biomechanics.

PLoS One 2020 24;15(1):e0228071. Epub 2020 Jan 24.

Section for Sports Traumatology, M51, Bispebjerg and Frederiksberg Hospital, Copenhagen, Denmark.

The forward lunge (FL) may be a promising movement to assess functional outcome after ACL reconstruction. Thus, we aimed to investigate the FL movement pattern before and after ACL reconstruction with a comparison to healthy controls to determine if differences were present. Twenty-eight ACL injured participants and 28 matched healthy controls were included. They performed FL movements while sagittal plane biomechanics of the knee and electromyography (EMG) of nine leg muscles was assessed. The ACL injured group was tested before and 10 months after surgery. The perceived knee function and activity level was assessed by questionnaires. The ACL injured group performed the FL significantly slower than the controls before surgery (mean difference: 0.41 s [95%CI: 0.04-0.79 s; p<0.05]) while they performed the FL as fast as the controls after surgery (~28% movement time reduction post-surgery). Perceived knee function and activity level improved significantly post-surgery. The knee joint flexion angle, extensor moment, power, angular velocity in the ACL injured group did not differ from pre to post-surgery. For the ACL injured group, the peak knee extensor moment observed both pre and post-surgery was significantly lower when compared to the controls. The EMG results showed minimal differences. In conclusion, at 10 months post-surgery, the FL was performed significantly faster and the movement time was comparable to that of the controls. While the perceived knee function and activity level improved post-surgery, the knee joint biomechanics were unchanged. This may reflect that knee joint function was not fully restored.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0228071PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6980669PMC
April 2020

Relationship of Knee Forces to Subjective Function Pre- and Post-ACL Reconstruction.

Med Sci Sports Exerc 2020 06;52(6):1338-1346

Department of Industrial Engineering, University of Bologna, Bologna, ITALY.

Purpose: Although basic objective measures (e.g., knee laxity, strength, and hop tests) have been related to subjective measures of function, associations between knee-specific objective and subjective measures have yet to be completed. The objective was to determine if knee joint contact and ligament forces differ between pre- and post-anterior cruciate ligament (ACL) reconstructed states and if these forces relate to their patient's respective subjective functional ability scores.

Methods: Twelve patients performed a hopping task before and after reconstruction. Magnetic resonance images and OpenSim were used to develop patient-specific models in static optimization and joint reaction analyses. Questionnaires concerning each patient's subjective functional ability were also collected and correlated with knee joint contact and ligament forces.

Results: No significant differences were observed between deficient and reconstructed groups with respect to knee joint contact or ligament forces. Nevertheless, there were several significant (P < 0.05) moderate to strong correlations between subjective and objective measures including Tegner activity level to contact force in both states (r = 0.67-0.76) and International Knee Documentation Committee to compressive and anterior shear forces (r = 0.64-0.66).

Conclusion: Knee-specific objective measures of a patient's functional capacity can represent their subjective ability, which explains this relationship to a greater extent than past anatomical and gross objective measures of function. This consolidation is imperative for improving the current rehabilitation schema as it allows for external validation of objective and subjective functional measures. With poor validation of subjective function against objective measures of function, the reinjury rate is unlikely to diminish, continuing the heavy financial burden on health care systems.
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http://dx.doi.org/10.1249/MSS.0000000000002258DOI Listing
June 2020

Predicting post-operative functional ability from pre-operative measures in ACL-injured individuals.

Scand J Med Sci Sports 2020 Jan 1;30(1):166-173. Epub 2019 Sep 1.

School of Rehabilitation Sciences, University of Ottawa, Ottawa, ON, Canada.

Purpose: This study aimed to quantify the relationship between objective and subjective measures of functional ability and determine if measures in the deficient (ACLd) state were correlated to, and capable of predicting a patient's objective and subjective measures in the reconstructed (ACLr) state.

Methods: Twenty ACL-injured participants completed hop and side cut movements prior to and 10 months post-reconstruction. Their subjective measures (Tegner, Lysholm, IKDC, KOOS, and KNEEs) were related to objective measures of functional ability (peak knee flexion, peak knee extensor moment, stiffness, knee joint center excursion (KJCE), and knee joint center boundary). Correlations were used to determine relationships between variables whereas regressions were used to identify ACLd score's predictive ability of an ACLr score.

Results: Relationships between objective and subjective measures were task and ACL status dependent with KJCE and stiffness most commonly being related to subjective scores. The greatest correlation was between knee stiffness and Tegner in the ACLr group during the side cut (r = 0.69). Peak knee flexion angle (adj. R  = 0.4-0.66) was the best objective predictor between ACLd and ACLr states while KOOS-ADL had the strongest correlations (r = 0.70-0.77) and Tegner had the greatest predictive power (odds ratio: 1.46-1.86) between states in both tasks.

Conclusion: Objective measures show a wide range of correlation to subjective measures with some being quite strong. Furthermore, objective measures in the ACLd state are more correlated and more often capable of predicting ACLr scores than the subjective measures of functional ability.
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http://dx.doi.org/10.1111/sms.13549DOI Listing
January 2020

Knee osteoarthritis among airport baggage handlers: A prospective cohort study.

Am J Ind Med 2019 11 26;62(11):951-960. Epub 2019 Aug 26.

National Institute of Public Health, University of Southern Denmark, Copenhagen, Denmark.

Background: Knee osteoarthritis is a common and often disabling disorder, which has been related to knee-straining work. However, exposure response relations are uncertain and there are few prospective studies. We studied prospectively if incident knee osteoarthritis is associated with cumulative exposure as an airport baggage handler, lifting on average 5000 kg/d.

Methods: The study is based on the Copenhagen Airport Cohort, a historical cohort of male baggage handlers and a reference group of unskilled men from the greater Copenhagen area, followed from 1990 to 2012. Cumulative years of employment as a baggage handler was based on information from company employment and union registers. Outcome was first hospital admission with a discharge diagnosis of knee osteoarthritis and/or knee replacement, ascertained from the Danish National Patient Register.

Results: The cohort contained 3442 baggage handlers and 65 511 workers in the reference group. The unadjusted incidence rate ratio (IRR) of knee osteoarthritis increased steeply with cumulative years as a baggage handler. Although the exposure-response pattern became weaker and statistically nonsignificant (P ≈ .10) when adjusting for age, the risk of knee osteoarthritis was still increased in baggage handlers at the highest exposure level. Additional analyses showed that the association between age and osteoarthritis was stronger for baggage handlers (IRR = 2.09; 95% CI: 1.68-2.60) than for referents (IRR = 1.58; 95% CI: 1.53-1.63), indicating that knee osteoarthritis occurred at a younger age among baggage handlers than in the reference group.

Conclusions: The results of this prospective cohort study support that long-term heavy lifting increases the risk of knee osteoarthritis.
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http://dx.doi.org/10.1002/ajim.23044DOI Listing
November 2019

Occupational lifting predicts hospital admission due to low back pain in a cohort of airport baggage handlers.

Int Arch Occup Environ Health 2020 01 26;93(1):111-122. Epub 2019 Aug 26.

National Institute of Public Health, University of Southern Denmark, Studiestræde 6, 1455, Copenhagen, Denmark.

Purpose: To examine if occupational lifting assessed as cumulative years as a baggage handler is associated with first-time hospital diagnosis or treatment for low back disorders.

Methods: This study is based on the Copenhagen Airport Cohort consisting of male baggage handlers performing heavy lifting every day and a reference group of unskilled men from the greater Copenhagen area during the period 1990-2012. We followed the cohort in the National Patient Register and Civil Registration System to obtain information on diagnoses, surgery, mortality, and migration. The outcomes were first-time hospital diagnosis or surgery for (1) lumbar disc herniation or (2) low back pain (LBP).

Results: Baggage handlers (N = 3473) had a higher incidence rate of LBP, but not of lumbar disc herniation, compared to the reference group (N = 65,702). Baggage handlers with longer employment had a higher incidence of LBP compared to baggage handlers with shorter employment. The linear association of cumulative years as a baggage handler on LBP was significantly increased with an incidence rate ratio of 1.16 (95% CI 1.07-1.25) for a 5-year increase of employment as baggage handler.

Conclusions: In this large cohort study, we found an increased incidence of LBP among baggage handlers compared to the reference group with indications of a dose-response relationship between years of employment and the outcome. For baggage handlers working on the apron, the incidence was particularly increased before introduction of technical lifting equipment, suggesting that preventive measures to reduce cumulative work load may have a positive effect.
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http://dx.doi.org/10.1007/s00420-019-01470-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6989598PMC
January 2020

Outcome Measures After ACL Injury in Pediatric Patients: A Scoping Review.

Orthop J Sports Med 2019 Jul 30;7(7):2325967119861803. Epub 2019 Jul 30.

Department of Physical and Occupational Therapy, Bispebjerg and Frederiksberg Hospital, Copenhagen, Denmark.

Background: The incidence of anterior cruciate ligament (ACL) injuries in children is increasing. However, no standardized core set of outcome measures exists for evaluating pediatric ACL injuries.

Purpose: To perform a scoping review of the literature to identify patient-reported outcome measures (PROMs) and objective outcome measures used to evaluate pediatric patients after ACL injury and to classify these in accordance with the International Classification of Functioning, Disability, and Health (ICF) domains.

Study Design: Systematic review; Level of evidence, 4.

Methods: The literature was systematically searched with the PubMed, EMBASE, CINAHL, and PEDro databases. The inclusion criteria were Danish, Norwegian, Swedish, German, or English language; publication between 2010 and 2018; pediatric ACL injury (patients ≤15 years old); and outcome measures. The selected papers were screened for title, abstract, and full text in accordance with predefined inclusion and exclusion criteria.

Results: A total of 68 papers (4286 patients; mean ± SD age, 12.2 ± 2.3 years) were included. Nineteen PROMs and 11 objective outcome measures were identified. The most frequently reported PROMs were the International Knee Documentation Committee (IKDC) Subjective Knee Form (51% of studies), Lysholm scoring scale (46% of studies) and Tegner activity rating scale (37% of studies). Additionally, return to sport was reported in 41% of studies. The most frequent objective measures were knee laxity (76% of studies), growth disturbances (69% of studies), range of motion (41% of studies), and muscle strength (21% of studies). With respect to the ICF domains, the IKDC covered all 3 ICF health domains, the Lysholm score covered the Body Structure and Function and the Activity Limitation domains, while the Tegner score covered the Participation Restriction domain. Objectively measured knee joint laxity, range of motion, and muscle strength covered 1 domain (Body Structure and Function).

Conclusion: Pediatric patients with ACL injury were mainly evaluated subjectively with the IKDC and objectively by knee joint laxity. No consensus exists in the evaluation of children after ACL injury. The majority of applied outcome measures are developed for adults. To cover the ICF health domains, future research needs to consider reliable and valid outcome measures relevant for pediatric patients with ACL injury.
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http://dx.doi.org/10.1177/2325967119861803DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6685120PMC
July 2019

Experimental muscle pain of the vastus medialis reduces knee joint extensor torque and alters quadriceps muscle contributions as revealed through musculoskeletal modeling.

Clin Biomech (Bristol, Avon) 2019 07 22;67:27-33. Epub 2019 Apr 22.

School of Rehabilitation Sciences, University of Ottawa, 451 Smyth Rd, Ottawa, ON K1H 8M5, Canada; School of Human Kinetics, University of Ottawa, 125 University Pr, Ottawa, ON K1N 1A2, Canada. Electronic address:

Background: Voluntary activation deficit of the quadriceps muscle group is a common symptom in populations with knee joint injury. Musculoskeletal modeling and simulations can improve our understanding of pathological conditions; however, they are mathematically complex which can limit their clinical application. A practical subject-specific modeling framework is introduced to evaluate knee extensor inhibition and muscle force contributions to isometric knee joint torques in healthy adults with and without experimentally induced quadriceps muscle pain.

Methods: A randomized cross-over placebo controlled study design was used. Subject-specific maximum knee joint extension torque and quadriceps electromyographic data from 13 uninjured young adults were combined in a modeling framework to determine optimal muscle strength scaling parameters and ideal torque. Strength deficit ratios (experimental torque/ideal torque) and individual muscle contribution to experimental torque was computed before and after intramuscular hypertonic (pain inducing) and isotonic (sham) saline was injected to the vastus medialis.

Findings: Decreased experimental knee extension torque (-8%) and vastus medialis electromyography (-26%) amplitude pre- to post- hypertonic injection was observed. Correspondingly, significant decreases in the knee extensor strength deficit ratio (-18%) and percent contribution of vastus medialis to experimental torque (-24%) was observed pre- to post- hypertonic injection. No differences were observed with isotonic injections, confirming the validity of the model.

Interpretation: Our practical method to estimate strength ratios can be easily implemented within a musculoskeletal modeling framework to improve the validity of model estimates. This, in turn, can increase our understanding of the relationship between neuromuscular deficits and functional outcomes in patient populations.
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http://dx.doi.org/10.1016/j.clinbiomech.2019.04.005DOI Listing
July 2019

Assessment of objective dynamic knee joint control in anterior cruciate ligament deficient and reconstructed individuals.

Knee 2019 Jun 4;26(3):578-585. Epub 2019 Apr 4.

School of Human Kinetics, University of Ottawa, Canada; Department of Physical and Occupational Therapy, Copenhagen University Hospital, Denmark. Electronic address:

Background: There is a lack of objective dynamic knee joint control measures that can be related to the status of the anterior cruciate ligament (ACL). The purpose of this study was to introduce two novel measures and apply a third to determine how dynamic knee joint control changes in relation to ACL status during dynamic movements.

Methods: Twenty patients (13 male) were tested pre- (ACLd) and 10-months post- (ACLr) ACL reconstructive surgery and matched to an uninjured participant (CON). Kinetic and kinematic data were synchronously recorded with a force platform and motion capture system. Three objective control measures including dynamic angular stiffness, knee joint center excursion (KJCE), and knee joint center boundary (KJCB) were assessed for each participant when completing the side cut and hop tasks.

Results: During the side cut, stiffness was found to be significantly lower in ACLd (0.06 ± 0.01 Nm/kg/°) and ACLr (0.07 ± 0.02 Nm/kg/°) compared to CON (0.08 ± 0.02 Nm/kg/°), while there were no differences in stiffness during the hop. No significant differences were observed in the KJCE during the side cut, while KJCE was significantly greater (p = 0.006) during the hop in CON compared to the ACLd. There were no differences in KJCB.

Conclusions: These high-functioning ACL injured in both ACLd and ACLr phases, aside from reduced stiffness, were able to complete both tasks with similar dynamic control as the CON. Although improvements in self-perceived control between ACLd and ACLr have been observed, this lack of improvement in objective control demonstrates a gap between a patient's self-efficacy and the level of control.
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http://dx.doi.org/10.1016/j.knee.2019.02.013DOI Listing
June 2019

Opioid-Induced Reductions in Gait Variability in Healthy Volunteers and Individuals with Knee Osteoarthritis.

Pain Med 2019 11;20(11):2106-2114

The Parker Institute, Copenhagen University Hospital Bispebjerg-Frederiksberg, Copenhagen, Denmark.

Objective: To investigate differences in gait variability induced by two different single-dose opioid formulations and an inert placebo in healthy volunteers and knee osteoarthritis patients.

Design: Experimental, randomized, double-blinded, crossover study of inert placebo (calcium tablets), 50 mg of tapentadol, and 100 mg of tramadol.

Setting: Laboratory setting.

Subjects: Healthy volunteers and knee osteoarthritis patients.

Methods: At three visits, separated by seven days, one tablet was administered per visit according to the randomization code. At each visit, a baseline measurement was done before tablet administration, after which hourly measurements were performed for six hours, yielding a total of seven measurements per visit. Gait variability was measured by three-dimensional gait analysis, recorded during six minutes of continuous treadmill walking at self-selected speed. One hundred seventy gait cycles were identified from detection of clear events of the knee joint angle trajectories. Gait variability was assessed as average standard deviations over a gait cycle of the sacrum displacements and accelerations; sagittal plane ankle, knee, and hip joint angles; step widths; and stride times.

Results: Twenty-four opioid-naïve and neurologically intact participants (12 healthy volunteers and 12 knee osteoarthritis patients) were included and completed the experiment. Tapentadol reduced the variability of sacrum displacements and accelerations compared with placebo and tramadol. There were no differences between experimental conditions regarding the variability in lower-extremity joint angle variability, step widths, or stride times.

Conclusions: In opioid-naïve and neurologically intact individuals, tapentadol seems to reduce movement variability during treadmill walking, compared with placebo and tramadol. This can be interpreted as a loss of adaptability that might increase the risk of falling if the system is perturbed.
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http://dx.doi.org/10.1093/pm/pny286DOI Listing
November 2019

Effect of implementing magnetic resonance imaging for patient-specific OpenSim models on lower-body kinematics and knee ligament lengths.

J Biomech 2019 01 16;83:9-15. Epub 2018 Nov 16.

Faculty of Health Sciences, University of Ottawa, Canada; Department of Biomedical Sciences, University of Copenhagen, Denmark. Electronic address:

Background: OpenSim models are typically based on cadaver findings that are generalized to represent a wide range of populations, which curbs their validity. Patient-specific modelling through incorporating magnetic resonance imaging (MRI) improves the model's biofidelity with respect to joint alignment and articulations, muscle wrapping, and ligament insertions. The purpose of this study was to determine if the inclusion of an MRI-based knee model would elicit differences in lower limb kinematics and resulting knee ligament lengths during a side cut task.

Methods: Eleven participants were analyzed with the popular Rajagopal OpenSim model, two variations of the same model to include three and six degrees of freedom knee (DOF), and a fourth version featuring a four DOF MRI-based knee model. These four models were used in an inverse kinematics analysis of a side cut task and the resulting lower limb kinematics and knee ligament lengths were analyzed.

Results: The MRI-based model was more responsive to the movement task than the original Rajagopal model while less susceptible to soft tissue artifact than the unconstrained six DOF model. Ligament isometry was greatest in the original Rajagopal model and smallest in the six DOF model.

Conclusions: When using musculoskeletal modelling software, one must acutely consider the model choice as the resulting kinematics and ligament lengths are dependent on this decision. The MRI-based knee model is responsive to the kinematics and ligament lengths of highly dynamic tasks and may prove to be the most valid option for continuing with late-stage modelling operations such as static optimization.
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http://dx.doi.org/10.1016/j.jbiomech.2018.11.016DOI Listing
January 2019

Anterior cruciate ligament reconstruction improves subjective ability but not neuromuscular biomechanics during dynamic tasks.

Knee Surg Sports Traumatol Arthrosc 2019 Feb 10;27(2):636-645. Epub 2018 Oct 10.

School of Human Kinetics, University of Ottawa, 200 Lees Avenue, Ottawa, K1S 5S9, Canada.

Purpose: The purpose of this study was to identify high-functioning anterior cruciate ligament-deficient patients and assess the effects of reconstruction on their self-reported functionality, muscle activations and biomechanical properties.

Methods: Twenty young and active patients participated pre- (11.5 ± 14.3 months post-injury) and again 10.5 ± 1.7 months post-reconstruction and were individually matched to 20 healthy controls. Participants completed hop and side cut movements while patient-related outcome measures, lower limb electromyography, kinetic, and whole body kinematic data were collected. One-dimensional statistical parametric mapping was used to test for group differences (healthy vs deficient; deficient vs reconstructed; reconstructed vs healthy).

Results: When comparing healthy to anterior cruciate ligament-deficient participants, all questionnaires indicated significant lower subjective function while the only substantial biomechanical difference between these participants was a decreased knee extensor moment in both the hop (peak difference: 0.63 Nm/kg, p < 0.001) and side cut (peak difference: 0.76 Nm/kg, p < 0.001). When comparing patients' pre- and post-reconstruction, no biomechanical differences were observed whereas only half of the questionnaires (Tegner, Lysholm, KNEES-ADL, KNEES-Slackness, KNEES-Looseness, KNEES-Sport Behaviour, IKDC, and KOOS-QoL) indicated higher function in the reconstructed state. When comparing the reconstructed patients to the healthy participants, all questionnaires were still significantly higher in the healthy controls. The reconstructed group also had a smaller flexion angle (peak difference: 14.5°, p = 0.007) and knee extensor moment (peak difference: 0.62 Nm/kg, p < 0.001) during the hop and a smaller knee extensor moment (peak difference: 0.90 Nm/kg, p < 0.001) during the side-cut task.

Conclusion: At 10-months post-reconstruction, the current results indicate that in high-functioning anterior cruciate ligament-deficient patients, reconstruction had little impact on objective measures of functional ability during dynamic tasks although self-reported function was improved.

Level Of Evidence: Therapeutic prospective cohort study, Level II.
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http://dx.doi.org/10.1007/s00167-018-5189-7DOI Listing
February 2019

Differences in EMG-moment relationships between ACL-injured and uninjured adults during a weight-bearing multidirectional force control task.

J Orthop Res 2019 01 16;37(1):113-123. Epub 2018 Oct 16.

School of Rehabilitation Sciences, University of Ottawa, 200 Lees Ave, Rm E020, Ottawa, Ontario, Canada K1S 5L5.

Anterior cruciate ligament injury (ACLi) reduces mechanical knee joint stability. Differences in muscle activation patterns are commonly identified between ACLi individuals and uninjured controls (CON); however, how and which of these differences are adaptations to protect the knee or adversely increase risk of joint instability remain unclear. Since the neuromuscular system integrates activity of all muscles crossing the knee to create a moment-of-force that opposes an external load, this study sought to quantify differences in individual muscle electromyography (EMG)-moment relationships between ACLi and CON. Participants isometrically modulated ground reaction forces during a standing force matching protocol to elicit combinations of sagittal, frontal and transverse plane moments. Partial least squares regressions determined which internal joint moment(s) predicted activation of 10 leg muscles for each group. Compared to CON, ACLi demonstrated greater contribution of rectus femoris to knee extension, semitendinosus and gastrocnemii to knee flexion, and lateral gastrocnemii to knee external rotation moments. ACLi also showed lower contributions of biceps femoris to knee flexion, medial gastrocnemius to internal rotation, and varied hip muscle contributions to frontal plane hip moments. Between group differences in EMG-moment relationships during static conditions suggest neuromuscular contributions to sagittal plane stability increases after ACL injury, while knee stability during knee abduction and external rotation is reduced. Clinical Significance: Clinical assessments of ACLi should account for deficits in frontal and rotational plane stability by including tasks that elicit such loads. Improving hamstring muscle balance, hip abductor and gastrocnemius function may benefit ACLi rehabilitation interventions and should be studied further. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.
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http://dx.doi.org/10.1002/jor.24145DOI Listing
January 2019

A hierarchy in functional muscle roles at the knee is influenced by sex and anterior cruciate ligament deficiency.

Clin Biomech (Bristol, Avon) 2018 08 25;57:129-136. Epub 2018 Jun 25.

School of Rehabilitation Sciences, University of Ottawa, 200 Lees Avenue Ottawa, ON K1N 6N5, Canada; School of Human Kinetics, University of Ottawa, 200 Lees Avenue Ottawa, ON K1N 6N5, Canada. Electronic address:

Background: Sex-related neuromuscular differences have been linked to greater risk of anterior cruciate ligament injuries in females. Despite this, it remains unclear if sex-related differences are present after injury. This study sought to determine if sex differences are present in the functional roles of knee joint muscles in an anterior cruciate ligament deficient population.

Methods: An isometric, weight-bearing, force-generation protocol required injured and healthy males and females to modulate ground reaction forces. Electromyography was used to classify the functional role of 10 lower limb muscles in their contribution to knee joint stability during various loading directions. These roles were compared between the four groups at 12 loading directions using a directional analysis.

Findings: Functional muscle roles were different between groups, except for injured males and healthy females. Healthy males had either joint actuators or specific joint stabilisers, but no general stabilisers; the vastus medialis and lateralis of injured males and healthy females were classified as general stabilisers while injured females added the gluteus medialis and medial gastrocnemius as general stabilisers.

Interpretation: A population-based hierarchy in functional muscle roles was discovered. Healthy males demonstrated the most specific muscle roles, which can be viewed as more adaptive to variable loading conditions. The more generalised stabilisation strategies seen in injured males and females would alter joint loading which may be detrimental to the knee joint health over time. In summary, (1) these injuries alter muscle roles; (2) these alterations are sex-specific; (3) rehabilitation might be optimised if sex-differences are considered.
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http://dx.doi.org/10.1016/j.clinbiomech.2018.06.014DOI Listing
August 2018

Assessment of intersegmental coordination of rats during walking at different speeds - Application of continuous relative phase.

J Biomech 2018 05 4;73:168-176. Epub 2018 Apr 4.

Department of Nutrition, Exercise and Sports, University of Copenhagen, Copenhagen, Denmark.

The present study investigated the feasibility and reliability of continuous relative phase (CRP) and deviation phase (DP) to assess intersegmental hind limb coordination pattern and coordination variability in rats during walking. Twenty-six adult rats walked at 8 m/min, 12 m/min and 16 m/min while two-dimensional kinematics were recorded. Segment angles and segment angular velocities of the paw, shank and thigh on the left hind-limb were extracted from 15 strides and CRP was calculated for the paw-shank and shank-thigh coupling. The effect of walking speed on the time point average curve of the CRP (ACRP) and DP and on the mean ACRP and mean DP was established by statistical parametric mapping (SPM) and a one-way ANOVA for repeated measures. Absolute and relative reliability were assessed by measurement error and intra-class correlation coefficient. The SPM analysis revealed time dependent differences in the effect of speed. Thus, the CRP of the paw-shank coupling decreased with increasing speed during most of the gait cycle while the CRP of the shank-thigh coupling was decreased during the swing phase. The session-to-session reliability was fair to good for the coordination measure and poor for the variability measure.
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http://dx.doi.org/10.1016/j.jbiomech.2018.03.045DOI Listing
May 2018

Day-to-day reliability of gait characteristics in rats.

J Biomech 2018 04 7;72:247-251. Epub 2018 Mar 7.

Department of Biomedical Sciences, University of Copenhagen, Copenhagen, Denmark.

The purpose of the present study was to determine the day-to-day reliability in stride characteristics in rats during treadmill walking obtained with two-dimensional (2D) motion capture. Kinematics were recorded from 26 adult rats during walking at 8 m/min, 12 m/min and 16 m/min on two separate days. Stride length, stride time, contact time, swing time and hip, knee and ankle joint range of motion were extracted from 15 strides. The relative reliability was assessed using intra-class correlation coefficients (ICC(1,1)) and (ICC(3,1)). The absolute reliability was determined using measurement error (ME). Across walking speeds, the relative reliability ranged from fair to good (ICCs between 0.4 and 0.75). The ME was below 91 mm for strides lengths, below 55 ms for the temporal stride variables and below 6.4° for the joint angle range of motion. In general, the results indicated an acceptable day-to-day reliability of the gait pattern parameters observed in rats during treadmill walking. The results of the present study may serve as a reference material that can help future intervention studies on rat gait characteristics both with respect to the selection of outcome measures and in the interpretation of the results.
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http://dx.doi.org/10.1016/j.jbiomech.2018.02.035DOI Listing
April 2018

Injection of high dose botulinum-toxin A leads to impaired skeletal muscle function and damage of the fibrilar and non-fibrilar structures.

Sci Rep 2017 11 7;7(1):14746. Epub 2017 Nov 7.

Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark.

Botulinum-toxin A (BoNT/A) is used for a wide range of conditions. Intramuscular administration of BoNT/A inhibits the release of acetylcholine at the neuromuscular junction from presynaptic motor neurons causing muscle-paralysis. The aim of the present study was to investigate the effect of high dose intramuscular BoNT/A injections (6 UI = 60 pg) on muscle tissue. The gait pattern of the rats was significantly affected 3 weeks after BoNT/A injection. The ankle joint rotated externally, the rats became flat footed, and the stride length decreased after BoNT/A injection. Additionally, there was clear evidence of microstructural changes on the tissue level by as evidenced by 3D imaging of the muscles by Synchrotron Radiation X-ray Tomographic Microscopy (SRXTM). Both the fibrillar and the non-fibrillar tissues were affected. The volume fraction of fibrillary tissue was reduced significantly and the non-fibrillar tissue increased. This was accompanied by a loss of the linear structure of the muscle tissue. Furthermore, gene expression analysis showed a significant upregulation of COL1A1, MMP-2, TGF-b1, IL-6, MHCIIA and MHCIIx in the BoNT/A injected leg, while MHVIIB was significantly downregulated.

In Conclusion: The present study reveals that high dose intramuscular BoNT/A injections cause microstructural damage of the muscle tissue, which contributes to impaired gait.
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http://dx.doi.org/10.1038/s41598-017-14997-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5677119PMC
November 2017

Risk of subacromial shoulder disorder in airport baggage handlers: combining duration and intensity of musculoskeletal shoulder loads.

Ergonomics 2018 Apr 5;61(4):576-587. Epub 2017 Oct 5.

a National Institute of Public Health, University of Southern Denmark , Copenhagen , Denmark.

Musculoskeletal shoulder load among baggage handlers measured by combining duration and intensity based on biomechanical and epidemiological information may be a stronger predictor of subacromial shoulder disorders than baggage handler seniority. In 2012, a cohort of baggage handlers employed at Copenhagen Airport in 1990-2012, and a cohort of unskilled otherwise employed men answered a survey. Self-reported information on work tasks during employment in the airport in combination with work task specific biomechanically modelled forces in the shoulder joint was used to estimate shoulder load. Exposure measures were accumulated shoulder abduction moment, accumulated shoulder compression force, accumulated supraspinatus force and baggage handler seniority. The outcome was subacromial shoulder disorder registered in the Danish National Patient Register. When analyses were adjusted by all confounders except age, exposure variables showed close to significant associations with subacromial shoulder disorder. Results could not confirm our hypothesis that combined information on work task duration and shoulder load intensity was stronger associated with subacromial shoulder disorder than seniority. Practitioner Summary: In this study we sought to identify if the exposure to work-related musculoskeletal shoulder loading including duration and intensity among baggage handlers was associated with subacromial shoulder disorder. We found that there was an association but this was not stronger than that between baggage handler seniority and subacromial shoulder disorder.
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http://dx.doi.org/10.1080/00140139.2017.1382721DOI Listing
April 2018

Copenhagen Airport Cohort: air pollution, manual baggage handling and health.

BMJ Open 2017 05 6;7(5):e012651. Epub 2017 May 6.

National Institute of Public Health, University of Southern Denmark, Copenhagen, Denmark.

Purpose: Copenhagen Airport Cohort 1990-2012 presents a unique data source for studies of health effects of occupational exposure to air pollution (ultrafine particles) and manual baggage handling among airport employees. We describe the extent of information in the cohort and in the follow-up based on data linkage to the comprehensive Danish nationwide health registers. In the cohort, all information is linked to the personal identification number that also is used in Denmark Statistics demographic and socioeconomic databases and in the nationwide health registers.

Participants: The cohort covers 69 175 men in unskilled positions. The exposed cohort includes men in unskilled jobs employed at Copenhagen Airport in the period 1990-2012 either as baggage handlers or in other outdoor work. The reference cohort includes men in unskilled jobs working in the greater Copenhagen area.

Findings To Date: The cohort includes environmental Global Positioning System (GPS) measurements in Copenhagen Airport, information on job function/task for each calendar year of employment between 1990 and 2012, exposure to air pollution at residence, average weight of baggage lifted per day and lifestyle. By linkage to registers, we retrieved socioeconomic and demographic data and data on healthcare contacts, drug subscriptions, incident cancer and mortality.

Future Plans: The size of the cohort and the completeness of the register-based follow-up allow a more accurate assessment of the possible health risks of occupational exposure to ultrafine particles and manual baggage handling at airports than in previous studies. We plan to follow the cohort for the incidence of ischaemic heart diseases, cerebrovascular disease, lung and bladder cancer, asthma and chronic obstructive pulmonary disease, and further for associations between heavy manual baggage handling and musculoskeletal disorders.

Trial Registration: number 2012-41-0199.
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http://dx.doi.org/10.1136/bmjopen-2016-012651DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5777468PMC
May 2017

Predicting the Functional Roles of Knee Joint Muscles from Internal Joint Moments.

Med Sci Sports Exerc 2017 03;49(3):527-537

1School of Rehabilitation Sciences, University of Ottawa, Ottawa, ON, CANADA; 2Department of Neuroscience and Pharmacology, University of Copenhagen, Copenhagen, DENMARK; 3Section of Sportstraumatology M51, Bispebjerg Hospital, Copenhagen, DENMARK; and 4School of Human Kinetics, University of Ottawa, Ottawa, ON, CANADA.

Introduction: Knee muscles are commonly labeled as flexors or extensors and aptly stabilize the knee against sagittal plane loads. However, how these muscles stabilize the knee against adduction-abduction and rotational loads remains unclear. Our study sought 1) to classify muscle roles as they relate to joint stability by quantifying the relationship between individual muscle activation patterns and internal net joint moments in all three loading planes and 2) to determine whether these roles change with increasing force levels.

Methods: A standing isometric force matching protocol required subjects to modulate ground reaction forces to elicit various combinations and magnitudes of sagittal, frontal, and transverse internal joint moments. Surface EMG measured activities of 10 lower limb muscles. Partial least squares regressions determined which internal moment(s) were significantly related to the activation of individual muscles.

Results: Rectus femoris and tensor fasciae latae were classified as moment actuators for knee extension and hip flexion. Hamstrings were classified as moment actuators for hip extension and knee flexion. Gastrocnemius and hamstring muscles were classified as specific joint stabilizers for knee rotation. Vastii were classified as general joint stabilizers because activation was independent of moment generation. Muscle roles did not change with increasing effort levels.

Conclusions: Our findings indicate muscle activation is not dependent on anatomical orientation but perhaps on its role in maintaining knee joint stability in the frontal and transverse loading planes. This is useful for delineating the roles of biarticular knee joint muscles and could have implications in robotics, musculoskeletal modeling, sports sciences, and rehabilitation.
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http://dx.doi.org/10.1249/MSS.0000000000001125DOI Listing
March 2017

Joint dynamics and intra-subject variability during countermovement jumps in children and adults.

J Biomech 2016 09 21;49(13):2968-2974. Epub 2016 Jul 21.

Department of Neuroscience and Pharmacology, University of Copenhagen, Blegdamsvej 3B, 2200 Copenhagen N, Denmark.

The present study investigated lower limb joint work, lower limb joint energy transport and intra-subject variation of the joint dynamics during countermovement jumps in children and adults. Twelve healthy men and eleven healthy boys performed ten maximal countermovement jumps. Three dimensional kinematics and kinetics were recorded in synchrony. Hip, knee and ankle joint eccentric and concentric work, joint energy transfer, intra-subject variation of joint moment, joint power and joint moment components were calculated. The children had lower eccentric and concentric hip work and lower eccentric knee work but no group difference was observed in the concentric knee joint work and ankle joint work. Eccentric hip and knee joint energy transfer and concentric hip joint energy transfer were higher in adults. The children had higher intra-subject variation in the eccentric and concentric hip joint work, hip joint moment and hip and knee joint power. Higher intra-subject variation was observed in horizontal joint reaction force components for the children and higher intra-subject variation in the segment angular inertia components was observed for the adults. The joint dynamics of children during countermovement jumps were less efficient in producing proximal joint work, transferring energy through joint centres and characterized by a higher intra-subject variation.
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http://dx.doi.org/10.1016/j.jbiomech.2016.07.010DOI Listing
September 2016

A Cohort Study on Meniscal Lesions among Airport Baggage Handlers.

PLoS One 2016 14;11(6):e0157336. Epub 2016 Jun 14.

National Institute of Public Health, University of Southern Denmark, Copenhagen, Denmark.

Meniscal lesions are common and may contribute to the development of knee arthrosis. A few case-control and cross-sectional studies have identified knee-straining work as risk factors for meniscal lesions, but exposure-response relations and the role of specific exposures are uncertain, and previous results may be sensitive to reporting and selection bias. We examined the relation between meniscal lesions and cumulative exposure to heavy lifting in a prospective register-based study with complete follow-up and independent information on exposure and outcome. We established a cohort of unskilled men employed at Copenhagen Airport or in other companies in the metropolitan Copenhagen area from 1990 to 2012 (the Copenhagen Airport Cohort). The cohort at risk included 3,307 airport baggage handlers with heavy lifting and kneeling or squatting work tasks and 63,934 referents with a similar socioeconomic background and less knee-straining work. Baggage handlers lifted suitcases with an average weight of approximately 15 kg, in total approximately five tonnes during a 9-hour workday. The cohort was followed in the National Patient Register and Civil Registration System. The outcome was a first time hospital diagnosis or surgery of a meniscal lesion. Baggage handlers had a higher incidence of meniscal lesions than the referents. Within baggage handlers spline regression showed that the incidence rate ratio was 1.91 (95% confidence interval: 1.29-2.84) after five years as a baggage handler and then decreased slowly to reach unity after approximately 30 years, adjusted for effects of potential confounders. This relation between baggage handling and meniscal lesions was present for work on the apron which involves lifting in a kneeling or squatting position, but not in the baggage hall, which only involves lifting in standing positions. The results support that long-term heavy lifting in a kneeling or squatting position is a risk factor for the development of symptomatic meniscal lesions.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0157336PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4907513PMC
July 2017

Reliable Gait Recognition Using 3D Reconstructions and Random Forests - An Anthropometric Approach.

J Forensic Sci 2016 05 6;61(3):637-48. Epub 2016 Jan 6.

Department of Neuroscience and Pharmacology, University of Copenhagen, Blegdamsvej 3, DK-2200, Copenhagen, Denmark.

Photogrammetric measurements of bodily dimensions and analysis of gait patterns in CCTV are important tools in forensic investigations but accurate extraction of the measurements are challenging. This study tested whether manual annotation of the joint centers on 3D reconstructions could provide reliable recognition. Sixteen participants performed normal walking where 3D reconstructions were obtained continually. Segment lengths and kinematics from the extremities were manually extracted by eight expert observers. The results showed that all the participants were recognized, assuming the same expert annotated the data. Recognition based on data annotated by different experts was less reliable achieving 72.6% correct recognitions as some parameters were heavily affected by interobserver variability. This study verified that 3D reconstructions are feasible for forensic gait analysis as an improved alternative to conventional CCTV. However, further studies are needed to account for the use of different clothing, field conditions, etc.
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http://dx.doi.org/10.1111/1556-4029.13015DOI Listing
May 2016
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