Neuromuscular Activity during Cycling Performance in Hot/Dry and Hot/Humid Conditions

Abstract

To determine the relationships between limiting factors and neuromuscular activity during a self-paced 20-km cycling time trial and evaluate the effect of environmental conditions on fatigue indices. Methods: Ten endurance-trained and heat-acclimated athletes performed in three conditions (ambient temperature, relative humidity): HUMID (30 °C, 90%), DRY (35 °C, 46%) and NEUTRAL (22 °C, 55%). Voluntary muscular contractions and electromagnetic stimulations were recorded before and after the time trials to assess fatigue. The data on performance, temperature, heat storage, electromyogram, heart rate and rating of perceived exertion data were analyzed. Results: Performance was impaired in DRY and HUMID compared with NEUTRAL environment (p < 0.05). The force developed by the vastus lateral muscle during stimulation of the femoral nerve remained unchanged across conditions. The percentage of integrated electromyogram activity, normalized by the value attained during the pre-trial maximal voluntary contraction, decreased significantly throughout the trial only in HUMID condition (p < 0.01). Neuromuscular activity in peripheral skeletal muscle started to fall from the 11th km in HUMID and the 15th km in DRY condition, although core temperature did not reach critical values. Conclusions: These alterations suggest that afferences from core/skin temperature regulate the central neural motor drive, reducing the active muscle recruited during prolonged exercise in the heat in order to prevent the system from hyperthermia.

What Is the Evidence That Dietary Macronutrient Composition Influences Exercise Performance? A Narrative Review

“…As a result, the rate of rise in RPE can be used to predict the moment at which exercise will terminate [112]. In addition, the control acts 'in anticipation' [113][114][115]. Whilst researching this topic, I discovered the paper by Baldwin et al [42], already discussed in part.…”

New Advances in Human Thermophysiology

“…The papers published in this Special Issue discuss the topics of greatest concern to the population and the scientific community from the perspective of human thermophysiology. Most of the articles evaluate how the physiological response during or after exercise is affected by extreme environmental conditions, such as high temperatures [ 7 ], hot and humid environments [ 8 , 9 ], dehydration status [ 10 ] or even cold environments [ 11 ]. This issue is of concern to society as a whole, since global warming is an established threat, greatly impacting our environment [ 12 ].…”

“…The articles published in the Special Issue “Human Thermophysiology” in Life have provided interesting results that allow a more specific understanding of how human beings behave during or after physical exercise in extreme environmental conditions. Heat and high humidity can reduce muscle recruitment as a method of preventing body hyperthermia [ 8 ]. In this sense, a lower gradient between the core and skin temperature could be responsible for a reduction in the performance [ 8 ], in agreement with previous studies [ 14 , 15 ].…”

“…Heat and high humidity can reduce muscle recruitment as a method of preventing body hyperthermia [ 8 ]. In this sense, a lower gradient between the core and skin temperature could be responsible for a reduction in the performance [ 8 ], in agreement with previous studies [ 14 , 15 ]. On the other hand, Melo-Marins et al showed how dehydration decreases glutathione levels, which have an important antioxidant property [ 10 ].…”

“…All these studies are important for understanding factors that limit performance and developing effective prevention strategies. Baillot et al recommended methods to decrease skin temperature or mimic cold sensations (e.g., menthol vaporization on the skin during exercise) during exercise in hot and high-humidity environments [ 8 ]. In addition, the results of Chabert et al could recommend the modification of the breathed air temperature during aerobic exercise [ 9 ].…”