Publications by authors named "Lars Nybo"

104 Publications

Quantifying the impact of heat on human physical work capacity; part III: the impact of solar radiation varies with air temperature, humidity, and clothing coverage.

Int J Biometeorol 2021 Oct 28. Epub 2021 Oct 28.

Environmental Ergonomics Research Centre, Loughborough University, Loughborough, LE11 3TU, UK.

Heat stress decreases human physical work capacity (PWC), but the extent to which solar radiation (SOLAR) compounds this response is not well understood. This study empirically quantified how SOLAR impacts PWC in the heat, considering wide, but controlled, variations in air temperature, humidity, and clothing coverage. We also provide correction equations so PWC can be quantified outdoors using heat stress indices that do not ordinarily account for SOLAR (including the Heat Stress Index, Humidex, and Wet-Bulb Temperature). Fourteen young adult males (7 donning a work coverall, 7 with shorts and trainers) walked for 1 h at a fixed heart rate of 130 beats∙min1, in seven combinations of air temperature (25 to 45°C) and relative humidity (20 or 80%), with and without SOLAR (800 W/m from solar lamps). Cumulative energy expenditure in the heat, relative to the work achieved in a cool reference condition, was used to determine PWC%. Skin temperature was the primary determinant of PWC in the heat. In dry climates with exposed skin (0.3 Clo), SOLAR caused PWC to decrease exponentially with rising air temperature, whereas work coveralls (0.9 Clo) negated this effect. In humid conditions, the SOLAR-induced reduction in PWC was consistent and linear across all levels of air temperature and clothing conditions. Wet-Bulb Globe Temperature and the Universal Thermal Climate Index represented SOLAR correctly and did not require a correction factor. For the Heat Stress Index, Humidex, and Wet-Bulb Temperature, correction factors are provided enabling forecasting of heat effects on work productivity.
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http://dx.doi.org/10.1007/s00484-021-02205-xDOI Listing
October 2021

Effects of Weather Parameters on Endurance Running Performance: Discipline Specific Analysis of 1258 Races.

Med Sci Sports Exerc 2021 Oct 14. Epub 2021 Oct 14.

FAME Laboratory, Department of Physical Education and Sport Science, University of Thessaly, Trikala, Greece University of Canberra, Research Institute for Sport and Exercise, Canberra, Australia Aspetar Orthopaedic and Sports Medicine Hospital, Research and Scientific Support Department, Doha, Qatar Department of Nutrition, Exercise and Sports, Section for Integrative Physiology, University of Copenhagen, Denmark.

Introduction: This study evaluated how single or combinations of weather parameters (temperature, humidity, wind speed, solar load) affect peak performance during endurance running events and identify which events are most vulnerable to varying weather conditions.

Methods: Results for the marathon, 50 km race-walk, 20 km race-walk, 10,000 m, 5,000 m and 3,000 m-steeplechase were obtained from the official websites of large competitions. We identified meteorological data from nearby (8.9 ± 9.3 km) weather stations for 1258 races held between 1936 and 2019 across 42 countries, enabling analysis of 7867 athletes.

Results: The Wet-Bulb Globe Temperature (WBGT) across races ranged from -7 to 33 °C, with 27% of races taking place in cold/cool, 47% in neutral, 18% in moderate heat, 7% in high heat, and 1% in extreme heat conditions, according to the World Athletics classification. Machine learning decision trees (R2 values: 0.21-0.58) showed that air temperature (importance score: 40%) was the most important weather parameter. But, when used alone, air temperature had lower predictive power (R2 values: 0.04-0.34) than WBGT (R2 values: 0.11-0.47). Conditions of 7.5-15 °C WBGT (or 10-17.5 °C air temperature) increase the likelihood for peak performance. For every degree WBGT outside these optimum conditions, performance declined by 0.3-0.4%.

Conclusion: More than one-quarter of endurance running events were held in moderate, high, or extreme heat and this number reaches one-half for events other than the marathon. All four weather parameters must be evaluated to mitigate the health and performance implications of exercising at maximal intensities in a hot environment with athletes adopting heat mitigation strategies when possible.
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http://dx.doi.org/10.1249/MSS.0000000000002769DOI Listing
October 2021

Current and projected regional economic impacts of heatwaves in Europe.

Nat Commun 2021 10 4;12(1):5807. Epub 2021 Oct 4.

Department of Nutrition and Exercise Sciences, University of Copenhagen (NEXS), 2100, Copenhagen, Denmark.

Extreme heat undermines the working capacity of individuals, resulting in lower productivity, and thus economic output. Here we analyse the present and future economic damages due to reduced labour productivity caused by extreme heat in Europe. For the analysis of current impacts, we focused on heatwaves occurring in four recent anomalously hot years (2003, 2010, 2015, and 2018) and compared our findings to the historical period 1981-2010. In the selected years, the total estimated damages attributed to heatwaves amounted to 0.3-0.5% of European gross domestic product (GDP). However, the identified losses were largely heterogeneous across space, consistently showing GDP impacts beyond 1% in more vulnerable regions. Future projections indicate that by 2060 impacts might increase in Europe by a factor of almost five compared to the historical period 1981-2010 if no further mitigation or adaptation actions are taken, suggesting the presence of more pronounced effects in the regions where these damages are already acute.
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http://dx.doi.org/10.1038/s41467-021-26050-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8490455PMC
October 2021

Health vs. wealth: Employer, employee and policy-maker perspectives on occupational heat stress across multiple European industries.

Temperature (Austin) 2021 14;8(3):284-301. Epub 2020 Dec 14.

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

Successful implementation of cooling strategies obviously depends on identifying effective interventions, but in industrial settings, it is equally important to consider feasibility and economic viability. Many cooling interventions are available, but the decision processes affecting adoption by end-users are not well elucidated. We therefore arranged two series of meetings with stakeholders to identify knowledge gaps, receive feedback on proposed cooling interventions, and discuss factors affecting implementation of heat-health interventions. This included four meetings attended by employers, employees, and health and safety officers (n = 41), and three meetings attended primarily by policy makers (n = 74), with feedback obtained via qualitative and quantitative questionnaires and focus group discussions. On a 10-point scale, both employers and employees valued worker safety (9.1 ± 1.8; mean±SD) and health (8.5 ± 1.9) as more important than protecting company profits (6.3 ± 2.3). Of the respondents, 41% were unaware of any cooling strategies at their company and of those who were aware, only 30% thought the interventions were effective. Following presentation of proposed interventions, the respondents rated "facilitated hydration", "optimization of clothing/protective equipment", and "rescheduling of work tasks" as the top-three preferred solutions. The main barriers for adopting cooling interventions were cost, feasibility, employer perceptions, and legislation. In conclusion, preventing negative health and safety effects was deemed to be more important than preventing productivity loss. Regardless of work sector or occupation, both health and wealth were emphasized as important parameters and considered as somewhat interrelated. However, a large fraction of the European worker force lacks information on effective measures to mitigate occupational heat stress. : OH-Stress: Occupational heat stress; WBGT: Wet Bulb Globe Temperature.
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http://dx.doi.org/10.1080/23328940.2020.1852049DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8409781PMC
December 2020

Proposed framework for forecasting heat-effects on motor-cognitive performance in the Summer Olympics.

Temperature (Austin) 2021 20;8(3):262-283. Epub 2021 Aug 20.

Department of Nutrition, Exercise and Sports, Section for Integrative Physiology, University of Copenhagen, Copenhagen N, Copenhagen, Denmark.

Heat strain impairs performance across a broad spectrum of sport disciplines. The impeding effects of hyperthermia and dehydration are often ascribed to compromised cardiovascular and muscular functioning, but expert performance also depends on appropriately tuned sensory, motor and cognitive processes. Considering that hyperthermia has implications for central nervous system (CNS) function and fatigue, it is highly relevant to analyze how heat stress forecasted for the upcoming Olympics may influence athletes. This paper proposes and demonstrates the use of a framework combining expected weather conditions with a heat strain and motor-cognitive model to analyze the impact of heat and associated factors on discipline- and scenario-specific performances during the Tokyo 2021 games. We pinpoint that hyperthermia-induced central fatigue may affect prolonged performances and analyze how hyperthermia may impair complex motor-cognitive performance, especially when accompanied by either moderate dehydration or exposure to severe solar radiation. Interestingly, several short explosive performances may benefit from faster cross-bridge contraction velocities at higher muscle temperatures in sport disciplines with little or no negative heat-effect on CNS fatigue or motor-cognitive performance. In the analyses of scenarios and Olympic sport disciplines, we consider thermal impacts on "motor-cognitive factors" such as decision-making, maximal and fine motor-activation as well as the influence on central fatigue and pacing. From this platform, we also provide perspectives on how athletes and coaches can identify risks for their event and potentially mitigate negative motor-cognitive effects for and optimize performance in the environmental settings projected.
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http://dx.doi.org/10.1080/23328940.2021.1957367DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8409751PMC
August 2021

Skeletal muscle phenotype and game performance in elite women football players.

Scand J Med Sci Sports 2021 Aug 24. Epub 2021 Aug 24.

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

We combined game activity analyses with skeletal muscle phenotypes and comprehensive physiological testing to elucidate factors of importance for physical performance in elite women's football. GPS-data from an experimental game, sprint and endurance testing, and muscle tissue analysis of metabolic enzyme activity, protein expression and fiber type composition were completed for international top-level women players (n = 20; age; 23 ± 4 yrs, height; 166 ± 10 cm, weight; 60 ± 8 kg; VO ; 51 ± 6 ml/min/kg). Muscle monocarboxylate transporter 4 (MCT4) protein expression explained 46% of the variance in total game distance, while the ability to maintain high-intensity running (HIR) during the final 15 min of the game correlated to myosin heavy chain 1 (MHCI) and Na -K ATPase β1, FXYD1 (phospholemman) and superoxide dismutase 2 (SOD2) protein expression (range: r = 0.51-0.71; all p < 0.05). Total HIR distance correlated with (MHCIIa) protein expression (r = 0.51; p < 0.05), while muscle Na /H exchanger 1 (NHE1) protein explained 36% of the variance in game sprint distance (p < 0.05). Total game accelerations (actions >4 m/s ) correlated with platelet endothelial cell adhesion molecule (PECAM-1) protein expression (r = 0.51; p < 0.05), while concentric knee flexor strength explained 42-62% of the variance in intense decelerations (>4 m/s ). In conclusion, for elite women players' game endurance performance and resistance to end-game fatigue were affected by monocarboxylate transporter expression and myosin heavy chain profile. HIR was also correlated to ion transporter expression and muscle antioxidative capacity. Finally, the importance of functional strength and measures of muscle vascularization in relation to total game decelerations and accelerations, respectively, illustrates the complex physiological demands in elite women's football.
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http://dx.doi.org/10.1111/sms.14022DOI Listing
August 2021

Reducing the health effects of hot weather and heat extremes: from personal cooling strategies to green cities.

Lancet 2021 08;398(10301):709-724

Center for Health and the Global Environment, University of Washington, WA, USA.

Heat extremes (ie, heatwaves) already have a serious impact on human health, with ageing, poverty, and chronic illnesses as aggravating factors. As the global community seeks to contend with even hotter weather in the future as a consequence of global climate change, there is a pressing need to better understand the most effective prevention and response measures that can be implemented, particularly in low-resource settings. In this Series paper, we describe how a future reliance on air conditioning is unsustainable and further marginalises the communities most vulnerable to the heat. We then show that a more holistic understanding of the thermal environment at the landscape and urban, building, and individual scales supports the identification of numerous sustainable opportunities to keep people cooler. We summarise the benefits (eg, effectiveness) and limitations of each identified cooling strategy, and recommend optimal interventions for settings such as aged care homes, slums, workplaces, mass gatherings, refugee camps, and playing sport. The integration of this information into well communicated heat action plans with robust surveillance and monitoring is essential for reducing the adverse health consequences of current and future extreme heat.
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http://dx.doi.org/10.1016/S0140-6736(21)01209-5DOI Listing
August 2021

Hot weather and heat extremes: health risks.

Lancet 2021 Aug;398(10301):698-708

Thermal Ergonomics Laboratory, Sydney, NSW, Australia; Sydney School of Health Sciences, Sydney, NSW, Australia; Sydney School of Public Health, Sydney, NSW, Australia; Faculty of Medicine and Health, Charles Perkins Centre, Sydney, NSW, Australia.

Hot ambient conditions and associated heat stress can increase mortality and morbidity, as well as increase adverse pregnancy outcomes and negatively affect mental health. High heat stress can also reduce physical work capacity and motor-cognitive performances, with consequences for productivity, and increase the risk of occupational health problems. Almost half of the global population and more than 1 billion workers are exposed to high heat episodes and about a third of all exposed workers have negative health effects. However, excess deaths and many heat-related health risks are preventable, with appropriate heat action plans involving behavioural strategies and biophysical solutions. Extreme heat events are becoming permanent features of summer seasons worldwide, causing many excess deaths. Heat-related morbidity and mortality are projected to increase further as climate change progresses, with greater risk associated with higher degrees of global warming. Particularly in tropical regions, increased warming might mean that physiological limits related to heat tolerance (survival) will be reached regularly and more often in coming decades. Climate change is interacting with other trends, such as population growth and ageing, urbanisation, and socioeconomic development, that can either exacerbate or ameliorate heat-related hazards. Urban temperatures are further enhanced by anthropogenic heat from vehicular transport and heat waste from buildings. Although there is some evidence of adaptation to increasing temperatures in high-income countries, projections of a hotter future suggest that without investment in research and risk management actions, heat-related morbidity and mortality are likely to increase.
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http://dx.doi.org/10.1016/S0140-6736(21)01208-3DOI Listing
August 2021

The Impacts of Sun Exposure on Worker Physiology and Cognition: Multi-Country Evidence and Interventions.

Int J Environ Res Public Health 2021 07 20;18(14). Epub 2021 Jul 20.

FAME Laboratory, Department of Physical Education and Sport Science, University of Thessaly, 42100 Trikala, Greece.

Background: A set of four case-control ( = 109), randomized-controlled ( = 7), cross-sectional ( = 78), and intervention ( = 47) studies was conducted across three countries to investigate the effects of sun exposure on worker physiology and cognition.

Methods: Physiological, subjective, and cognitive performance data were collected from people working in ambient conditions characterized by the same thermal stress but different solar radiation levels.

Results: People working under the sun were more likely to experience dizziness, weakness, and other symptoms of heat strain. These clinical impacts of sun exposure were not accompanied by changes in core body temperature but, instead, were linked with changes in skin temperature. Other physiological responses (heart rate, skin blood flow, and sweat rate) were also increased during sun exposure, while attention and vigilance were reduced by 45% and 67%, respectively, compared to exposure to a similar thermal stress without sunlight. Light-colored clothes reduced workers' skin temperature by 12-13% compared to darker-colored clothes.

Conclusions: Working under the sun worsens the physiological heat strain experienced and compromises cognitive function, even when the level of heat stress is thought to be the same as being in the shade. Wearing light-colored clothes can limit the physiological heat strain experienced by the body.
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http://dx.doi.org/10.3390/ijerph18147698DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8303297PMC
July 2021

Muscle Contractile Characteristics During Exhaustive Dynamic Exercise and Recovery.

Front Physiol 2021 2;12:660099. Epub 2021 Jul 2.

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

Our aim was to provide an assessment of human muscle twitch characteristics during and following an exhaustive dynamic exercise to explore temporal alterations of the rate of force development (RFD) and relaxation (RFR). Eleven healthy participants (mean age ± SD: 24 ± 3 years) completed a dynamic knee-extensor exercise in randomized order at three different intensities, eliciting exhaustion after ∼9 min (56 ± 10 W), ∼6 min (60 ± 10 W), and ∼4 min (63 ± 10 W), in addition to a low-intensity (28 ± 5 W) bout. In a novel setup, an electrical doublet stimulation of m. vastus lateralis was applied during exercise (every 30 s) and recovery for frequent evaluation of key contractile properties (maximal force, RFD, RFR, and electromechanical delay) in addition to M-wave characteristics. RFD and RFR remained stable throughout the low-intensity trial but declined in all exhaustive trials to reach a similar level of ∼40% of pre-exercise values at task failure but with the exponential decay augmented by intensity. Following exhaustion, there was a fast initial recovery of RFD and RFR to ∼80% of pre-exercise values within 1 min, followed by a longer suppression at this level. The M-wave characteristics remained unchanged during all trials. In conclusion, this is the first study to quantify the intensity-dependent alterations of RFD and RFR during and after exhaustive dynamic exercise in humans. A hypothesized reduction and fast reversion of RFD was confirmed, and a surprising compromised RFR is reported. The present unique experimental approach allows for novel insight to exercise-induced alterations in human muscle contractile properties which is relevant in health and disease.
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http://dx.doi.org/10.3389/fphys.2021.660099DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8283014PMC
July 2021

Occupational Heat Stress: Multi-Country Observations and Interventions.

Int J Environ Res Public Health 2021 06 10;18(12). Epub 2021 Jun 10.

FAME Laboratory, Department of Physical Education and Sport Science, University of Thessaly, 42100 Trikala, Greece.

Background: Occupational heat exposure can provoke health problems that increase the risk of certain diseases and affect workers' ability to maintain healthy and productive lives. This study investigates the effects of occupational heat stress on workers' physiological strain and labor productivity, as well as examining multiple interventions to mitigate the problem.

Methods: We monitored 518 full work-shifts obtained from 238 experienced and acclimatized individuals who work in key industrial sectors located in Cyprus, Greece, Qatar, and Spain. Continuous core body temperature, mean skin temperature, heart rate, and labor productivity were collected from the beginning to the end of all work-shifts.

Results: In workplaces where self-pacing is not feasible or very limited, we found that occupational heat stress is associated with the heat strain experienced by workers. Strategies focusing on hydration, work-rest cycles, and ventilated clothing were able to mitigate the physiological heat strain experienced by workers. Increasing mechanization enhanced labor productivity without increasing workers' physiological strain.

Conclusions: Empowering laborers to self-pace is the basis of heat mitigation, while tailored strategies focusing on hydration, work-rest cycles, ventilated garments, and mechanization can further reduce the physiological heat strain experienced by workers under certain conditions.
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http://dx.doi.org/10.3390/ijerph18126303DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8296111PMC
June 2021

Muscle metabolism and impaired sprint performance in an elite women's football game.

Scand J Med Sci Sports 2021 Jun 25. Epub 2021 Jun 25.

School of Physical Education and Sport Science, University of Thessaly, Trikala, Greece.

The present study examined skeletal muscle metabolism and changes in repeated sprint performance during match play for n = 20 competitive elite women outfield players. We obtained musculus vastus lateralis biopsies and blood samples before, after, and following intense periods in each half of a friendly match, along with 5 × 30-meter sprint tests and movement pattern analyses (10-Hz S5 Global Positioning System [GPS]). Muscle glycogen decreased by 39% and 42% after an intense period of the second half and after the match, respectively, compared to baseline (p < 0.05). Post-match, 80% type I fibers and 69% type II fibers were almost empty or completely empty of glycogen. Muscle lactate was higher (p < 0.05) after the intense period of the first half and post-match compared to baseline (14.3 ± 4.6 (±SEM) and 12.9 ± 5.7 vs. 6.4 ± 3.7 mmol/kg d.w.). Muscle phosphocreatine was reduced (p < 0.05) by 16% and 12%, respectively, after an intense period in the first and second half compared to baseline. Blood lactate and glucose increased during the match and peaked at 8.4 ± 2.0 and 7.9 ± 1.2 mmol/L, respectively. Mean 5 × 30 m sprint time declined by 3.2 ± 1.7 and 7.0 ± 2.1% after the first and second half, respectively, and 4.7 ± 1.6% (p < 0.05) after an intense period in the first half compared to baseline. In conclusion, match play in elite female football players resulted in marked glycogen depletion in both fiber types, which may explain fatigue at the end of a match. Repeated sprint ability was impaired after intense periods in the first half and after both halves, which may be associated with the observed muscle metabolite perturbations.
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http://dx.doi.org/10.1111/sms.13970DOI Listing
June 2021

Aerobic fitness as a parameter of importance for labour loss in the heat.

J Sci Med Sport 2021 Aug 8;24(8):824-830. Epub 2021 May 8.

Environmental Ergonomics Research Centre, School of Design and Creative Arts, Loughborough University, UK. Electronic address:

Objectives: To derive an empirical model for the impact of aerobic fitness (maximal oxygen consumption; V̇O in mL∙kg∙min) on physical work capacity (PWC) in the heat.

Design: Prospective, repeated measures.

Methods: Total work completed during 1 h of treadmill walking at a fixed heart rate of 130 b∙min was assessed in 19 young adult males across a variety of warm and hot climate types, characterised by wet-bulb globe temperatures (WBGT) ranging from 12 to 40 °C. For data presentation and obtaining initial parameter estimates for modelling, participants were grouped into low (n = 6, 74 trials), moderate (n = 8, 76 trials), and high (n = 5, 29 trials) fitness, with group mean V̇O 42, 52, and 64 mL∙kg∙min respectively. For the heated conditions (WBGT 18 to 40 °C), we calculated PWC% by expressing total energy expenditure (kJ above resting) in each trial relative to that achieved in a cool reference condition (WBGT = 12 °C = 100% PWC).

Results: The relative reduction in energy expenditure (PWC%) caused by heat was significantly smaller by up to 16% for the fit participants compared to those with lower aerobic capacity. V̇O also modulated the relationship between sweat rate and body temperature changes to increasing WBGT. Including individual V̇O data in the PWC prediction model increased the predicting power by 4%.

Conclusions: Incorporating individual V̇O improved the predictive power of the heat stress index WBGT for Physical Work Capacity in the heat. The largest impact of V̇O on PWC was observed at a WBGT between 25 and 35 °C.
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http://dx.doi.org/10.1016/j.jsams.2021.05.002DOI Listing
August 2021

Performance effects of periodized carbohydrate restriction in endurance trained athletes - a systematic review and meta-analysis.

J Int Soc Sports Nutr 2021 May 17;18(1):37. Epub 2021 May 17.

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

Endurance athletes typically consume carbohydrate-rich diets to allow for optimal performance during competitions and intense training. However, acute exercise studies have revealed that training or recovery with low muscle glycogen stimulates factors of importance for mitochondrial biogenesis in addition to favourable metabolic adaptations in trained athletes. Compromised training quality and particularly lower intensities in peak intervals seem to be a major drawback from dietary interventions with chronic carbohydrate (CHO) restriction. Therefore, the concept of undertaking only selected training sessions with restricted CHO availability (periodized CHO restriction) has been proposed for endurance athletes. However, the overall performance effect of this concept has not been systematically reviewed in highly adapted endurance-trained athletes. We therefore conducted a meta-analysis of training studies that fulfilled the following criteria: a) inclusion of females and males demonstrating a VOmax ≥ 55 and 60 ml · kg · min, respectively; b) total intervention and training periods ≥ 1 week, c) use of interventions including training and/or recovery with periodized carbohydrate restriction at least three times per week, and d) measurements of endurance performance before and after the training period. The literature search resulted in 407 papers of which nine studies fulfilled the inclusion criteria. The subsequent meta-analysis demonstrated no overall effect of CHO periodization on endurance performance compared to control endurance training with normal (high) CHO availability (standardized mean difference = 0.17 [- 0.15, 0.49]; P = 0.29). Based on the available literature, we therefore conclude that periodized CHO restriction does not per se enhance performance in endurance-trained athletes. The review discusses different approaches to CHO periodization across studies with a focus on identifying potential physiological benefits.
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http://dx.doi.org/10.1186/s12970-021-00435-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8127206PMC
May 2021

Prolonged facemask use in the heat worsens dyspnea without compromising motor-cognitive performance.

Temperature (Austin) 2020 Oct 9;8(2):160-165. Epub 2020 Oct 9.

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

Within the context of the COVID-19 pandemic, the WHO endorses facemask use to limit aerosol-spreading of the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, concerns have been raised regarding facemask-associated dyspnea, thermal distress and self-reported impairment of cognition. Accordingly, we tested how facemask-use affects motor-cognitive performances of relevance for occupational safety. We hypothesized that mask use would affect cognitively dominated performances and thermal discomfort, but not alter whole-body thermal balance. Eight participants completed a facemask and a barefaced (control) trial, in a counterbalanced order, in 40°C and 20% humidity conditions. Motor-cognitive performance, physiological (rectal, mean skin and local facial temperatures) and perceptual (thermal comfort and dyspnea) measures were assessed at baseline and following 45 min of light work (100 W). Perceived dyspnea was aggravated with prolonged facemask use (p = 0.04), resulting in 36% greater breathlessness compared to control. However, no other differences were observed in motor-cognitive performance, physiological strain, or thermal discomfort. Contradicting negative self-reported impacts of facemask-use, only dyspnea was aggravated in the present study, thereby reinforcing global recommendations of mask use, even in hot environments. (Funded by: European Union's Horizon 2020 research and innovation program under the grant agreement No 668786).
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http://dx.doi.org/10.1080/23328940.2020.1826840DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8098073PMC
October 2020

Force-velocity-power profiling of maximal effort sprinting, jumping and hip thrusting: Exploring the importance of force orientation specificity for assessing neuromuscular function.

J Sports Sci 2021 Sep 6;39(18):2115-2122. Epub 2021 May 6.

Institute for Nutrition, Exercise and Sports, Department of Integrative Physiology, University of Copenhagen, Copenhagen, Denmark.

Comprehensive information regarding neuromuscular function, as assessed through force-velocity-power (FVP) profiling, is of importance for training optimization in athletes. However, neuromuscular function is highly task-specific, potentially governed by dissimilarity of the overall orientation of forceapplication. The hip thrust (HT) exercise is thought to be of relevance for sprinting considering its antero-posterior force orientation and considerable hip-extensor recruitment, however, the association between their respective FVP profiles remains unexplored. Therefore, to address the concept of force orientation specificity within FVP profiling, the maximal theoretical neuromuscular capabilities of 41 professional male footballers (22.1 ± 4.1 years, 181.8 ± 6.4 cm, 76.4 ± 5.5 kg) were assessed during sprint acceleration, squat jumping (SJ) and the HT exercise. No significant associations were observed for maximal theoretical force or velocity between the three FVP profiling modalities, however, maximal theoretical power (Pmax) was correlated between sprinting and SJ (r = 0.73, P < 0.001) and HT and SJ (r = 0.44, P = 0.01), but not between sprinting and HT (r = 0.18, P = 0.36). In conclusion, although Pmax may be considered a somewhat universal lower-extremity capability, neuromuscular function is associated with substantial task-specificity not solely governed by the overall direction of force orientation.
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http://dx.doi.org/10.1080/02640414.2021.1920128DOI Listing
September 2021

Effect of a Simulated Heat Wave on Physiological Strain and Labour Productivity.

Int J Environ Res Public Health 2021 03 15;18(6). Epub 2021 Mar 15.

Department of Automation, Biocybernetics and Robotics, Jozef Stefan Institute, 1000 Ljubljana, Slovenia.

Background: The aim of the study was to investigate the effect of a simulated heat-wave on the labour productivity and physiological strain experienced by workers.

Methods: Seven males were confined for ten days in controlled ambient conditions. A familiarisation day was followed by three (pre, during, and post-heat-wave) 3-day periods. During each day volunteers participated in a simulated work-shift incorporating two physical activity sessions each followed by a session of assembly line task. Conditions were hot (work: 35.4 °C; rest: 26.3 °C) during, and temperate (work: 25.4 °C; rest: 22.3 °C) pre and post the simulated heat-wave. Physiological, biological, behavioural, and subjective data were collected throughout the study.

Results: The simulated heat-wave undermined human capacity for work by increasing the number of mistakes committed, time spent on unplanned breaks, and the physiological strain experienced by the participants. Early adaptations were able to mitigate the observed implications on the second and third days of the heat-wave, as well as impacting positively on the post-heat-wave period.

Conclusions: Here, we show for first time that a controlled simulated heat-wave increases workers' physiological strain and reduces labour productivity on the first day, but it promotes adaptations mitigating the observed implications during the subsequent days.
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http://dx.doi.org/10.3390/ijerph18063011DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7998810PMC
March 2021

The HEAT-SHIELD project - Perspectives from an inter-sectoral approach to occupational heat stress.

J Sci Med Sport 2021 Aug 8;24(8):747-755. Epub 2021 Mar 8.

Department of Nutrition, Exercise and Sports, University of Copenhagen, Denmark. Electronic address:

Objectives: To provide perspectives from the HEAT-SHIELD project (www.heat-shield.eu): a multi-national, inter-sectoral, and cross-disciplinary initiative, incorporating twenty European research institutions, as well as occupational health and industrial partners, on solutions to combat negative health and productivity effects caused by working on a warmer world.

Methods: In this invited review, we focus on the theoretical and methodological advancements developed to combat occupational heat stress during the last five years of operation.

Results: We outline how we created climate forecast models to incorporate humidity, wind and solar radiation to the traditional temperature-based climate projections, providing the basis for timely, policy-relevant, industry-specific and individualized information. Further, we summarise the industry-specific guidelines we developed regarding technical and biophysical cooling solutions considering effectiveness, cost, sustainability, and the practical implementation potential in outdoor and indoor settings, in addition to field-testing of selected solutions with time-motion analyses and biophysical evaluations. All recommendations were adjusted following feedback from workshops with employers, employees, safety officers, and adjacent stakeholders such as local or national health policy makers. The cross-scientific approach was also used for providing policy-relevant information based on socioeconomic analyses and identification of vulnerable regions considered to be more relevant for political actions than average continental recommendations and interventions.

Discussion: From the HEAT-SHIELD experiences developed within European settings, we discuss how this inter-sectoral approach may be adopted or translated into actionable knowledge across continents where workers and societies are affected by escalating environmental temperatures.
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http://dx.doi.org/10.1016/j.jsams.2021.03.001DOI Listing
August 2021

An advanced empirical model for quantifying the impact of heat and climate change on human physical work capacity.

Int J Biometeorol 2021 Jul 5;65(7):1215-1229. Epub 2021 Mar 5.

Environmental Ergonomics Research Centre, School of Design and Creative Arts Loughborough University, Loughborough, Leicestershire, LE11 3TU, UK.

Occupational heat stress directly hampers physical work capacity (PWC), with large economic consequences for industries and regions vulnerable to global warming. Accurately quantifying PWC is essential for forecasting impacts of different climate change scenarios, but the current state of knowledge is limited, leading to potential underestimations in mild heat, and overestimations in extreme heat. We therefore developed advanced empirical equations for PWC based on 338 work sessions in climatic chambers (low air movement, no solar radiation) spanning mild to extreme heat stress. Equations for PWC are available based on air temperature and humidity, for a suite of heat stress assessment metrics, and mean skin temperature. Our models are highly sensitive to mild heat and to our knowledge are the first to include empirical data across the full range of warm and hot environments possible with future climate change across the world. Using wet bulb globe temperature (WBGT) as an example, we noted 10% reductions in PWC at mild heat stress (WBGT = 18°C) and reductions of 78% in the most extreme conditions (WBGT = 40°C). Of the different heat stress indices available, the heat index was the best predictor of group level PWC (R = 0.96) but can only be applied in shaded conditions. The skin temperature, but not internal/core temperature, was a strong predictor of PWC (R = 0.88), thermal sensation (R = 0.84), and thermal comfort (R = 0.73). The models presented apply to occupational workloads and can be used in climate projection models to predict economic and social consequences of climate change.
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http://dx.doi.org/10.1007/s00484-021-02105-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8213606PMC
July 2021

COVID-19 and thermoregulation-related problems: Practical recommendations.

Temperature (Austin) 2020 Aug 6;8(1):1-11. Epub 2020 Aug 6.

VGGM, Arnhem, The Netherlands.

The COVID-19 pandemic started in the cold months of the year 2020 in the Northern hemisphere. Concerns were raised that the hot season may lead to additional problems as some typical interventions to prevent heat-related illness could potentially conflict with precautions to reduce coronavirus transmission. Therefore, an international research team organized by the Global Health Heat Information Network generated an inventory of the specific concerns about this nexus and began to address the issues. Three key thermal and covid-19 related topics were highlighted: 1) For the general public, going to public cool areas in the hot season interferes with the recommendation to stay at home to reduce the spread of the virus. Conflicting advice makes it necessary to revise national heat plans and alert policymakers of this forecasted issue. 2) For medical personnel working in hot conditions, heat strain is exacerbated due to a reduction in heat loss from wearing personal protective equipment to prevent contamination. To avoid heat-related injuries, medical personnel are recommended to precool and to minimize the increase in body core temperature using adopted work/rest schedules, specific clothing systems, and by drinking cold fluids. 3) Fever, one of the main symptoms of COVID-19, may be difficult to distinguish from heat-induced hyperthermia and a resting period may be necessary prior to measurement to avoid misinterpretation. In summary, heat in combination with the COVID-19 pandemic leads to additional problems; the impact of which can be reduced by revising heat plans and implementing special measures attentive to these compound risks.
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http://dx.doi.org/10.1080/23328940.2020.1790971DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7849778PMC
August 2020

Distribution of concurrent training sessions does not impact endurance adaptation.

J Sci Med Sport 2021 Mar 19;24(3):291-296. Epub 2020 Sep 19.

Department of Nutrition, Exercise and Sports, University of Copenhagen, Denmark. Electronic address:

Objectives: Optimized concurrent training regimes are warranted in physical training of military-, law enforcement- and rescue-personnel. This study investigated if four 15-min endurance training sessions weekly improve aerobic capacity and performance more than one 60-min endurance session weekly during the initial phase of a Basic Military Training program.

Design: A randomized training intervention study with functional and physiological tests before and after the intervention.

Methods: Military conscripts (n=290) were randomly allocated to three groups completing 9 weeks training. Weekly training consisted of four endurance and four strength training sessions lasting 15min each ('Micro-training': MIC); one strength and one endurance session lasting 60min each ('Classical-training': CLA) or two 60min sessions of standard military training ('Control-training': CON).

Results: Both 12-min (∼7-10%) and shuttle run performance (∼35-42%) improved (P≤0.001) similarly in all groups. Likewise, functional 2-min maximal repetition exercise capacity increased (P≤0.05) similarly in all groups (Lunges ∼17-24 %; PushUp ∼10-20%; AbdominalFlexions∼21-23%). Peak oxygen uptake changes depended on group (P≤0.05) with increases (P≤0.01) in MIC (7±7%, n=23) and CON (12±18%, n=17) and no changes in CLA. Maximal m. vastus lateralis citrate synthase activity decreased 14±26% (P≤0.001, n=18) in CLA. Likewise, maximal m. vastus lateralis 3-hydroxyacyl-CoA dehydrogenase activity decreased 8±17% in MIC (n=28) and 14±24% in CLA (n=18).

Conclusions: Four 15-min endurance training sessions weekly improves running performance and strength-endurance similarly to one 60min session. Peak oxygen uptake only increases with more than one endurance session weekly and leg muscle oxidative capacity appears reduced after basic military training.
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http://dx.doi.org/10.1016/j.jsams.2020.09.009DOI Listing
March 2021

Sustainable solutions to mitigate occupational heat strain - an umbrella review of physiological effects and global health perspectives.

Environ Health 2020 09 4;19(1):95. Epub 2020 Sep 4.

Department of Nutrition, Exercise and Sports, Section for Integrative Physiology, University of Copenhagen, Copenhagen N, Denmark.

Background: Climate change is set to exacerbate occupational heat strain, the combined effect of environmental and internal heat stress on the body, threatening human health and wellbeing. Therefore, identifying effective, affordable, feasible and sustainable solutions to mitigate the negative effects on worker health and productivity, is an increasingly urgent need.

Objectives: To systematically identify and evaluate methods that mitigate occupational heat strain in order to provide scientific-based guidance for practitioners.

Methods: An umbrella review was conducted in biomedical databases employing the following eligibility criteria: 1) ambient temperatures > 28 °C or hypohydrated participants, 2) healthy adults, 3) reported psychophysiological (thermal comfort, heart rate or core temperature) and/or performance (physical or cognitive) outcomes, 4) written in English, and 5) published before November 6, 2019. A second search for original research articles was performed to identify interventions of relevance but lacking systematic reviews. All identified interventions were independently evaluated by all co-authors on four point scales for effectiveness, cost, feasibility and environmental impact.

Results: Following screening, 36 systematic reviews fulfilled the inclusion criteria. The most effective solutions at mitigating occupational heat strain were wearing specialized cooling garments, (physiological) heat acclimation, improving aerobic fitness, cold water immersion, and applying ventilation. Although air-conditioning and cooling garments in ideal settings provide best scores for effectiveness, the limited applicability in certain industrial settings, high economic cost and high environmental impact are drawbacks for these solutions. However, (physiological) acclimatization, planned breaks, shading and optimized clothing properties are attractive alternative solutions when economic and ecological sustainability aspects are included in the overall evaluation.

Discussion: Choosing the most effective solution or combinations of methods to mitigate occupational heat strain will be scenario-specific. However, this paper provides a framework for integrating effectiveness, cost, feasibility (indoors and outdoor) and ecologic sustainability to provide occupational health and safety professionals with evidence-based guidelines.
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http://dx.doi.org/10.1186/s12940-020-00641-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7487490PMC
September 2020

Leg extension force-velocity imbalance has negative impact on sprint performance in ball-game players.

Sports Biomech 2020 Jul 14:1-14. Epub 2020 Jul 14.

Department of Integrative Physiology, Faculty of Science, University of Copenhagen, Copenhagen, Denmark.

Ballistic actions are imperative in sports where performance depends on power production across a relevant range of contraction- and movement velocities. Force-velocity-power () profiling provides information regarding neuromuscular capabilities and vertical performances, but knowledge regarding its associative value towards horizontal movements is scarce. Therefore, we conducted profiling and analysed associations with uni- and multidirectional ballistic performance tasks in 27 international- to national-level athletes (18.9 ± 2.6 years, 182.9 ± 7.1 cm and 79.2 ± 11.9 kg). Low to moderate correlations were observed between theoretical maximal power (max) and horizontal acceleration (R = -0.43), speed (R = -0.64), sprint (R = -0.60) and agility (R = -0.59) performances. Force-velocity imbalance (Fv) significantly (P ≤ 0.05) strengthened the correlations towards sprinting ability (from -0.60 to -0.74) and agility (from -0.59 to -0.68), however, both correlations remaining weaker than for jumping performances (R = 0.78-0.86). In conclusion, profiling provides information of importance for horizontal and vertical performances with a significant positive effect of max, but negative effect of Fv. Assessment of lower-extremity neuromuscular capabilities through profiling and associated development of training programmes targeting compensation of either force- or velocity deficit may benefit the ability to utilise a given power potential.
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http://dx.doi.org/10.1080/14763141.2020.1775877DOI Listing
July 2020

Football facing a future with global warming: perspectives for players health and performance.

Br J Sports Med 2021 Mar 1;55(6):297-298. Epub 2020 Jul 1.

Centre of Health Sciences, Faculty of Natural and Health Sciences, University of the Faroe Islands, Thorshavn, Faroe Islands.

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http://dx.doi.org/10.1136/bjsports-2020-102193DOI Listing
March 2021

Muscle Metabolism and Fatigue during Simulated Ice Hockey Match-Play in Elite Players.

Med Sci Sports Exerc 2020 10;52(10):2162-2171

Department of Nutrition, Exercise and Sport Sciences, University of Copenhagen, Copenhagen, DENMARK.

Purpose: The present study investigated muscle metabolism and fatigue during simulated elite male ice hockey match-play.

Methods: Thirty U20 male national team players completed an experimental game comprising three periods of 8 × 1-min shifts separated by 2-min recovery intervals. Two vastus lateralis biopsies were obtained either during the game (n = 7) or pregame and postgame (n = 6). Venous blood samples were drawn pregame and at the end of the first and last periods (n = 14). Activity pattern and physiological responses were continuously monitored using local positioning system and heart rate recordings. Further, repeated-sprint ability was tested pregame and after each period.

Results: Total distance covered was 5980 ± 199 m with almost half the distance covered at high skating speeds (>17 km·h). Average and peak on-ice heart rate was 84% ± 2% and 97% ± 2% of maximum heart rate, respectively. Muscle lactate increased (P ≤ 0.05) more than fivefold and threefold, whereas muscle pH decreased (P ≤ 0.05) from 7.31 ± 0.04 pregame to 6.99 ± 0.07 and 7.13 ± 0.11 during the first and last periods, respectively. Muscle glycogen decreased by 53% postgame (P ≤ 0.05) with ~65% of fast- and slow-twitch fibers depleted of glycogen. Blood lactate increased sixfold (P ≤ 0.05), whereas plasma free fatty acid levels increased 1.5-fold and threefold (P ≤ 0.05) after the first and last periods. Repeated-sprint ability was impaired (~3%; P ≤ 0.05) postgame concomitant with a ~10% decrease in the number of accelerations and decelerations during the second and last periods (P ≤ 0.05).

Conclusions: Our findings demonstrate that a simulated ice hockey match-play scenario encompasses a high on-ice heart rate response and glycolytic loading resulting in a marked degradation of muscle glycogen, particularly in specific sub-groups of fibers. This may be of importance both for fatigue in the final stages of a game and for subsequent recovery.
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http://dx.doi.org/10.1249/MSS.0000000000002370DOI Listing
October 2020

Direct exposure of the head to solar heat radiation impairs motor-cognitive performance.

Sci Rep 2020 05 8;10(1):7812. Epub 2020 May 8.

Department of Nutrition, Exercise and Sports, Section for integrative physiology, University of Copenhagen, 2200, Copenhagen N, Denmark.

Health and performance impairments provoked by thermal stress are societal challenges geographically spreading and intensifying with global warming. Yet, science may be underestimating the true impact, since no study has evaluated effects of sunlight exposure on human brain temperature and function. Accordingly, performance in cognitively dominated and combined motor-cognitive tasks and markers of rising brainstem temperature were evaluated during exposure to simulated sunlight (equal to ~1000 watt/m). Acute exposure did not affect any performance measures, whereas prolonged exposure of the head and neck provoked an elevation of the core temperature by 1 °C and significant impairments of cognitively dominated and motor task performances. Importantly, impairments emerged at considerably lower hyperthermia levels compared to previous experiments and to the trials in the presents study without radiant heating of the head. These findings highlight the importance of including the effect of sunlight radiative heating of the head and neck in future scientific evaluations of environmental heat stress impacts and specific protection of the head to minimize detrimental effects.
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http://dx.doi.org/10.1038/s41598-020-64768-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7210303PMC
May 2020

Impact of low-volume concurrent strength training distribution on muscular adaptation.

J Sci Med Sport 2020 Oct 4;23(10):999-1004. Epub 2020 Apr 4.

Department of Nutrition, Exercise and Sports, University of Copenhagen, Denmark. Electronic address:

Objectives: Military-, rescue- and law-enforcement personnel require a high physical capacity including muscular strength. The present study hypothesized that 9 weeks of volume matched concurrent short frequent training sessions increases strength more efficiently than less frequent longer training sessions.

Design: A randomized training intervention study with functional and physiological tests before and after the intervention.

Methods: Military conscripts (n=290) were assigned to micro-training (four 15-min strength and four 15-min endurance bouts weekly); classical-training (one 60-min strength and one 60-min endurance training session weekly) or a control-group (two 60-min standard military physical training sessions weekly).

Results: There were no group difference between micro-training and classical-training in measures of strength. Standing long jump remained similar while shotput performance was reduced (P≤0.001) in all three groups. Pull-up performance increased (P≤0.001) in micro-training (7.4±4.6 vs. 8.5±4.0 repetitions, n=59) and classical-training (5.7±4.1 vs. 7.1±4.2 repetitions, n=50). Knee extensor MVC increased (P≤0.01) in all groups (micro-training, n=30, 11.5±8.9%; classical-training, n=24, 8.3±11.5% and control, n=19, 7.5±11.8%) while elbow flexor and hand grip MVC remained similar. Micro-training increased (P≤0.05) type IIa percentage from 32.5±11.0% to 37.6±12.3% (n=20) and control-group increased (P≤0.01) type IIax from 4.4±3.0% to 11.6±7.9% (n=8). In control-group type I, fiber size increased (P≤0.05) from 5121±959μm to 6481±2084μm (n=5). Satellite cell content remained similar in all groups.

Conclusions: Weekly distribution of low-volume concurrent training completed as either eight 15-min bouts or two 60-min sessions of which 50% was strength training did not impact strength gains in a real-world setting.
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http://dx.doi.org/10.1016/j.jsams.2020.03.013DOI Listing
October 2020

Metformin does not compromise energy status in human skeletal muscle at rest or during acute exercise: A randomised, crossover trial.

Physiol Rep 2019 12;7(23):e14307

Section of Molecular Physiology, Department of Nutrition, Exercise and Sports, Faculty of Science, University of Copenhagen, Copenhagen, Denmark.

5´AMP-activated protein kinase (AMPK) is a mediator of a healthy metabolic phenotype in skeletal muscle. Metformin may exacerbate the energy disturbances observed during exercise leading to enhanced AMPK activation, and these disturbances may provoke early muscular fatigue. We studied acute (1 day) and short-term (4 days) effects of metformin treatment on AMPK and its downstream signaling network, in healthy human skeletal muscle and adipose tissue at rest and during exercise, by applying a randomized blinded crossover study design in 10 lean men. Muscle and fat biopsies were obtained before and after the treatment period at rest and after a single bout of exercise. Metformin treat ment elicited peak plasma and muscle metformin concentrations of 31 μM and 11 μM, respectively. Neither of the treatments affected AMPK activity in skeletal muscle and adipose at rest or during exercise. In contrast, whole-body stress during exercise was elevated as indicated by increased plasma lactate and adrenaline concentrations as well as increased heart rate and rate of perceived exertion. Also whole-body insulin sensitivity was enhanced by 4 days metformin treatment, that is reduced fasting plasma insulin and HOMA-IR. In conclusion, acute and short-term metformin treatment does not affect energy homeostasis and AMPK activation at rest or during exercise in skeletal muscle and adipose tissue of healthy subjects. However, metformin treatment is accompanied by slightly enhanced perceived exertion and whole-body stress which may provoke a lesser desire for physical activity in the metformin-treated patients.
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http://dx.doi.org/10.14814/phy2.14307DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6908741PMC
December 2019

Tramadol Does Not Improve Performance or Impair Motor Function in Trained Cyclists.

Med Sci Sports Exerc 2020 05;52(5):1169-1175

Department of Nutrition, Exercise and Sports (NEXS), University of Copenhagen, DENMARK.

Purpose: To investigate the hypothesis that a therapeutic oral dose of Tramadol improves cycling time trial performance and compromises motor-cognitive performance in highly trained cyclists.

Methods: Following two familiarization trials, 16 highly trained cyclists completed a preloaded time trial (1 h at 60% of peak power followed by a 15-km time trial) after ingestion of 100 mg Tramadol or placebo in a double-blind placebo-controlled counterbalanced crossover design separated by at least 4 d washout. Visuomotor tracking and math tasks were completed during the preload (n = 10) to evaluate effects on cognition and fine motor performance.

Results: Time trial mean power output (298 ± 42 W vs 294 ± 44 W) and performance (1474 ± 77 s vs 1483 ± 85 s) were similar with Tramadol and placebo treatment, respectively. In addition, there were no differences in perceived exertion, reported pain, blood pH, lactate, or bicarbonate concentrations across trials. Heart rate was higher (P < 0.001) during the Tramadol time trial (171 ± 8 bpm) compared with placebo (167 ± 9 bpm). None of the combined motor-cognitive tasks were impaired by Tramadol ingestion, in fact fine motor performance was slightly improved (P < 0.05) in the Tramadol trial compared with placebo.

Conclusions: In highly trained cyclists, ingestion of 100 mg Tramadol does not improve performance in a 15-km cycling time trial that was completed after a 1-h preload at 60% peak power. Additionally, a therapeutic dose of Tramadol does not compromise complex motor-cognitive or simple fine motor performances.
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http://dx.doi.org/10.1249/MSS.0000000000002217DOI Listing
May 2020

Hematological Adaptations to Prolonged Heat Acclimation in Endurance-Trained Males.

Front Physiol 2019 1;10:1379. Epub 2019 Nov 1.

The Centre of Inflammation and Metabolism and the Centre for Physical Activity Research, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark.

Heat acclimation is associated with plasma volume (PV) expansion that occurs within the first week of exposure. However, prolonged effects on hemoglobin mass (Hb) are unclear as intervention periods in previous studies have not allowed sufficient time for erythropoiesis to manifest. Therefore, Hb, intravascular volumes, and blood volume (BV)-regulating hormones were assessed with 5½ weeks of exercise-heat acclimation (HEAT) or matched training in cold conditions (CON) in 21 male cyclists [(mean ± SD) age: 38 ± 9 years, body weight: 80.4 ± 7.9 kg, VO: 59.1 ± 5.2 ml/min/kg]. HEAT ( = 12) consisted of 1 h cycling at 60% VO in 40C for 5 days/week in addition to regular training, whereas CON ( = 9) trained exclusively in cold conditions (<15C). Before and after the intervention, Hb and intravascular volumes were assessed by carbon monoxide rebreathing, while reticulocyte count and BV-regulating hormones were measured before, after 2 weeks and post intervention. Total training volume during the intervention was similar ( = 0.282) between HEAT (509 ± 173 min/week) and CON (576 ± 143 min/week). PV increased ( = 0.004) in both groups, by 303 ± 345 ml in HEAT and 188 ± 286 ml in CON. There was also a main effect of time ( = 0.038) for Hb with +34 ± 36 g in HEAT and +2 ± 33 g in CON and a tendency toward a higher increase in Hb in HEAT compared to CON (time × group interaction: = 0.061). The Hb changes were weakly correlated to alterations in PV ( = 0.493, = 0.023). Reticulocyte count and BV-regulating hormones remained unchanged for both groups. In conclusion, Hb was slightly increased following prolonged training in the heat and although the mechanistic link remains to be revealed, the increase could represent a compensatory response in erythropoiesis secondary to PV expansion.
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http://dx.doi.org/10.3389/fphys.2019.01379DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6842970PMC
November 2019
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