Beat the heat with the OSHA-NIOSH mobile app

Article de blogInternational audienc

Combining heat stress and moderate hypoxia reduces cycling time to exhaustion without modifying neuromuscular fatigue characteristics

Purpose: This study investigated the isolated and combined effects of heat [temperate (22°C/30% rH) vs. hot (35°C/40% rH)] and hypoxia [sea level (FiO2 0.21) vs. moderate altitude (FiO2 0.15)] on exercise capacity and neuromuscular fatigue characteristics. Methods: Eleven physically active subjects cycled to exhaustion at constant workload (66% of the power output associated with their maximal oxygen uptake in temperate conditions) in four different environmental conditions [temperate/sea level (control), hot/sea level (hot), temperate/moderate altitude (hypoxia) and hot/moderate altitude (hot+hypoxia)]. Torque and electromyography (EMG) responses following electrical stimulation of the tibial nerve (plantar-flexion; soleus) were recorded before and 5min after exercise. Results: Time to exhaustion was reduced (P0.05) did not reach significance. Maximal voluntary contraction torque, voluntary activation (twitch interpolation) and peak twitch torque decreased from pre- to post-exercise (−9±1, −4±1 and −6±1% all trials compounded, respectively; P<0.05), with no effect of the temperature or altitude. M-wave amplitude and root mean square activity were reduced (P<0.05) in hot compared to temperate conditions, while normalized maximal EMG activity did not change. Altitude had no effect on any measured parameters. Conclusion: Moderate hypoxia in combination with heat stress reduces cycling time to exhaustion without modifying neuromuscular fatigue characteristics. Impaired oxygen delivery or increased cardiovascular strain, increasing relative exercise intensity, may have also contributed to earlier exercise cessation

Validation of an ingestible temperature data logging and telemetry system during exercise in the heat

Aim: Intestinal temperature telemetry systems are promising monitoring and research tools in athletes. However, the additional equipment that must be carried to continuously record temperature data limits their use to training. The purpose of this study was to assess the validity and reliability of a new gastrointestinal temperature data logging and telemetry system (e-Celsius™) during water bath experimentation and exercise trials. Materials and Methods: Temperature readings of 23 pairs of e-Celsius (T(eC)) and VitalSense (T(VS)) ingestible capsules were compared to rectal thermistor responses (T(rec)) at 35, 38.5 and 42°C in a water bath. Devices were also assessed in vivo during steady-state cycling (n = 11) and intermittent running (n = 11) in hot conditions. Results: The water bath experiment showed T(VS) and T(eC) under-reported T(rec) (P<0.001). This underestimation of T(rec) also occurred during both cycling (mean bias vs T(VS): 0.21°C, ICC: 0.84, 95% CI: 0.66–0.91; mean bias vs. T(eC): 0.44°C, ICC: 0.68, 95% CI: 0.07–0.86, P<0.05) and running trials (mean bias vs. T(VS): 0.15°C, ICC: 0.92, 95% CI: 0.83–0.96; mean bias vs. T(eC): 0.25, ICC: 0.86, 95% CI: 0.61–0.94, P<0.05). However, calibrating the devices attenuated this difference during cycling and eliminated it during running. During recovery following cycling exercise, T(eC) and T(VS) were significantly lower than T(rec) despite calibration (P<0.01). Conclusion: These results indicate that both T(eC) and T(VS) under-report T(rec) during steady-state and intermittent exercise in the heat, with T(eC) predicting T(rec) with the least accuracy of the telemetry devices. It is therefore recommended to calibrate these devices at multiple temperatures prior to use

Repeated practice runs during on-snow training do not generate any measurable neuromuscular alterations in elite alpine skiers

Background Alpine skiers typically train using repeated practice runs requiring high bursts of muscle activity but there is little field-based evidence characterizing neuromuscular function across successive runs. Purpose To examine the impact of repeated ski runs on electromyographic activity (EMG) of the knee extensors and flexors in elite alpine skiers. Methods Nineteen national team alpine skiers were tested during regular ski training [Slalom (SL), Giant Slalom (GS), Super Giant Slalom and Downhill (Speed)] for a total of 39 training sessions. The surface EMG of the vastus lateralis (VL), rectus femoris (RF), vastus medialis (VM), biceps femoris (BF) and semimembranosus/semitendinosus (SMST) muscles was continuously recorded along with right knee and hip angles. The EMG root mean square signal was normalized to a maximal voluntary contraction (%MVC). The first and fourth runs of the training session were compared. Results There was no meaningful main effect of run on EMG relative activation time or mean power frequency beyond the skier's intrinsic variability. However, EMG activity of the vastii increased from the first to the fourth run in SL [VM, ~+3%MVC for IL and outside leg (OL), p = 0.035)], speed (VL, IL:+6%/OL:+11%, p = 0.015), and GS (VM, IL:0/OL:+7%, p < 0.001); the later with an interaction with leg (p < 0.001) due to a localized increase on the OL. The run time and turn time did not change from the first to the fourth run. There were no meaningful changes in angular velocities, amplitude of movement, or maximal and minimal angles. Conclusion Neuromuscular activity remains highly stable in elite skiers with low variability across four runs

Prehospital management of exertional heat stroke at sports competitions for Paralympic athletes

Objectives: To adapt key components of exertional heat stroke (EHS) prehospital management proposed by the International Olympic Committee (IOC) Adverse Weather Impact Expert Working Group for the Olympic Games Tokyo 2020 so that it is applicable for the Paralympic athletes.Methods: An expert working group representing members with research, clinical and lived sports experience from a Para sports perspective reviewed and revised the IOC consensus document of current best practice regarding the prehospital management of EHS.Results: Similar to Olympic competitions, Paralympic competitions are also scheduled under high environmental heat stress; thus, policies and procedures for EHS prehospital management should also be established and followed. For Olympic athletes, the basic principles of EHS prehospital care are: early recognition, early diagnosis, rapid, on-site cooling, and advanced clinical care. Although these principles also apply for Paralympic athletes, slight differences related to athlete physiology (e.g., autonomic dysfunction) and mechanisms for hands-on management (e.g., transferring the collapsed athlete or techniques for whole-body cooling) may require adaptation for care of the Paralympic athlete.Conclusions: Prehospital management of EHS in the Paralympic setting employs the same procedures as for Olympic athletes with some important alterations.</div

Mechanical asymmetries remain low-to-moderate during 30 min of self-paced treadmill running

Introduction: We characterized the magnitude and range of gait asymmetry during self-paced treadmill running.Methods: On an instrumented treadmill, twelve trained runners (11 males, 1 female) completed a 30-min self-paced run, during which participants were instructed to cover the most distance possible. Ground reaction force recordings at a constant velocity corresponding to 70% of their maximal aerobic velocity (13.3 ± 0.8 km.h−1) allowed for the measurement of running kinetics and kinematics, as well as the calculation of spring-mass characteristics at the beginning, middle, and end of the run (minutes 1, 14, and 29, respectively). Group mean asymmetry scores were assessed using the “symmetry angle” (SA) formulae, where scores of 0% and 100% represent perfect symmetry and perfect asymmetry, respectively.Results: There was no time effect on SA scores for any of the 13 biomechanical variables (p ≥ 0.128). Mean SA scores were &lt;2.5% for contact time (0.8% ± 0.7%), flight time (1.4% ± 0.6%), step frequency (0.7% ± 0.3%), duty factor (0.7% ± 0.3%), duration of braking (1.3% ± 0.7%) and push-off phases (0.9% ± 0.8%), as well as peak braking (2.3% ± 1.3%) and push-off forces (1.4% ± 0.9%). Mean SA scores were ≥2.5% for peak vertical loading rate (3.1% ± 1.7%), mean vertical loading rate (3.4% ± 2.1%), peak vertical forces (2.9% ± 2.2%), as well as vertical stiffness (5.2% ± 3.5%) and leg stiffness (2.5% ± 1.5%).Conclusion: Throughout a 30-min running time trial, there were consistently low-to-moderate mechanical asymmetries for spatiotemporal variables, kinetics, and spring-mass model characteristics. This suggests that trained runners maintained relatively even strides during the self-paced treadmill run, with lower extremities behaving similarly when controlling for velocity

Consensus recommendations on training and competing in the heat

Exercising in the heat induces thermoregulatory and other physiological strain that can lead to impairments in endurance exercise capacity. The purpose of this consensus statement is to provide up-to-date recommendations to optimize performance during sporting activities undertaken in hot ambient conditions. The most important intervention one can adopt to reduce physiological strain and optimize performance is to heat acclimatize. Heat acclimatization should comprise repeated exercise–heat exposures over 1–2 weeks. In addition, athletes should initiate competition and training in an euhydrated state and minimize dehydration during exercise. Following the development of commercial cooling systems (e.g., cooling vests), athletes can implement cooling strategies to facilitate heat loss or increase heat storage capacity before training or competing in the heat. Moreover, event organizers should plan for large shaded areas, along with cooling and rehydration facilities, and schedule events in accordance with minimizing the health risks of athletes, especially in mass participation events and during the first hot days of the year. Following the recent examples of the 2008 Olympics and the 2014 FIFA World Cup, sport governing bodies should consider allowing additional (or longer) recovery periods between and during events for hydration and body cooling opportunities when competitions are held in the heat