Football medic & scientist issue 20 - The Use of Heat and Hypoxia

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Pictured: Coventry City’s Marcus Tudgay lies injured during their League One match versus Milton Keynes Dons in March.

THE USE OF HEAT AND HYPOXIA IN THE PHYSICAL CONDITIONING

OF LOAD COMPROMISED PLAYERS FEATURE/CARL WELLS, BEN MACKENZIE & IAN AYLWARD Science and medical practitioners utilise novel training approaches in an attempt to optimise the physical condition of their athletes.

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ne such contemporary strategy is the periodised manipulation of the external training environment to increase the physical challenge and subsequent physiological response (Jebeau et al., 2016). When such an approach is applied acutely, the outcome is a reduction in the mechanical work performed for comparable or elevated cardiovascular effort (Vogt & Hoppeler, 2010). Such an intervention is particularly beneficial for dynamic load compromised players where due to either stage of rehabilitation or injury history, it is necessary to ensure the mechanical stress they are exposed to during periods of intensive conditioning or competition is reduced while maintaining aerobic fitness.

Hypoxia and heat are two environmental stressors commonly used to increase physiological strain for a reduced physical output (Garrett et al., 2010). The limited availability of atmospheric oxygen in moderate to severe hypoxia (<15%

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Fig 1 Average power output (W/Kg) for each 4 minute bout in hypoxic (13.5% atmospheric oxygen) and neutral (20.9% atmospheric oxygen) environments

football medic & scientist atmospheric oxygen) and redistribution of blood flow via vasodilation in heat (> 30 degrees Celsius) compromises the delivery of oxygenated blood to the exercising muscles, reducing physical output capabilities. Despite the manipulation of environmental temperature and oxygen content having such significant impact on the physical load placed upon an athlete, it has not been established how cardiovascular and physical output responses may vary between these two different physiological stressors. Due to the contrasting physiological adaptations induced by acute heat and hypoxic exposure, it may be the case that one environment is more appropriate than the other in achieving the desired physical stimulus for a load compromised player to optimise training gains. To help address this paucity in the knowledge, published findings (Mackenzie et al., 2016) collected in the Human Performance Laboratory at the National Football Centre St. Georgeâ&#x20AC;&#x2122;s Park will be presented in an attempt to provide guidance on the appropriate application of heat and hypoxia in the physical conditioning of load comprised athletes.

Fig 2. Average power output (W/Kg) for each 4 minute bout in heat (40 degrees Celsius) and neutral (24 degrees Celsius) environments.

The Study With institutional ethics approval, data was collected from 30 professional football players who attended the National Football Centre on the Professional Football Player Association intensive rehabilitation scheme. The aim of the study was to investigate whether differences exist in power output and heart rate during cycling in either severe heat or hypoxia compared to environmentally neutral conditions.

Players were allocated to either a heat or hypoxic exercise group, with the groups matched for aerobic fitness and training history. The heat and hypoxic groups performed the same exercise challenge of four bouts of maximal-intensity cycling for four minutes; with each bout separated by two minutes of passive recovery. The heat group performed the exercise challenge at 40 degrees Celsius, 50% humidity and 20.9% oxygen, while the hypoxic group exercised at 23 degrees Celsius, 50% humidity and 13.5% oxygen. The levels of hypoxia and heat used in the study were selected as they have both previously been classified as severely challenging environmental conditions (Sunderland et al., 2008; Swapnil et al., 2010). All players repeated the exercise challenge 48 hours later in environmentally neutral conditions (23 degrees Celsius, 50% humidity and 20.9% oxygen). For each four minute cycling bout in each environmental condition, average power output (W/Kg) and heart rate (b.min-1) were recorded. Analysis of variance was performed to measure mean differences between exercise bouts and environmental conditions.

Fig 3. Comparison of percentage power decrement for each 4 minute exercise bout between the hypoxic and heat environments.

Fig 3. Comparison of percentage power decrement for each 4 minute exercise bout between the hypoxic and heat environments.

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Pictured: West Ham Unitedâ&#x20AC;&#x2122;s Pedro Obiang receives treatment for an injury during the Premier League match against Leicester City at London Stadium.

The Findings Power Output Profiles As expected, analysis of the data revealed power output in hypoxia (Figure 1) and heat (Figure 2) for each exercise bout was lower than that achieved in neutral conditions. When the decrease in power output was averaged across the four bouts to provide a power degradation percentage for the entire session in each environment, the reduction in power output in hypoxia and heat compared to neutral conditions was similar at 9.8 and

10.4% respectively (Figure 3). However, further analysis of the data revealed a difference in the pattern of power degradation over the four bouts between the two environments. In hypoxia, power output was 7% lower than in neutral conditions during the first exercise bout.

This discrepancy increased to 10% by the second bout before plateauing to between 10 â&#x20AC;&#x201C; 12% for the remaining two bouts. In contrast, power output during the first exercise bout in the heat was only 2.7% lower than in the neutral environment before reducing sharply in a linear fashion

Fig 5. Percentage of maximum heart rate for each four minute exercise bout at 40 and 24 degrees Celsius.

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during the remaining exercise bouts, cumulating in W/Kg during the last 4 minutes in the heat being 20% lower than in the neutral environment.

Cardiovascular Reponses Cardiovascular load expressed as percentage of maximum heart rate increased in a linear fashion for each bout for all environmental conditions (figures 4 and 5), indicating an inability of the players to fully recover during the 2 minute rest periods. The highest cardiovascular strain was noted in heat during the 3rd and 4th bout, suggesting this environmental condition may provide the greatest cardiovascular load although the findings were not significantly different to those of hypoxia.

Why is there a difference in power degradation profile between heat and hypoxia?

The finding that power degradation profiles differ between heat and hypoxia may be explained by the time required for acute physiological adaptations to occur in response to a specific type of environmental stressor. The time course for the transport of atmospheric oxygen to the exercising muscle in trained athletes can have a time constant of less than 20 seconds (Wells et al., 2014). In a hypoxic environment, such a quick delivery of less oxygenated blood to the exercising muscles is likely to have an immediate impact on aerobic exercise performance.

There will have to be a reduction in work

football medic & scientist rate to counter the reduced oxygen availability for oxidative respiration when the cardiovascular system is already working close to its maximal capability for a sustained period. In the current study, when oxygen saturation was recorded at the end of each 4 minute bout during exercise in the hypoxic environment (Figure 6), oxygen saturation was notably reduced within the first bout and only decreased marginally during the remainder of the session, correlating with the observed pattern of power degradation. In contrast, thermal stress can take a period of time to manifest itself, and not impose physiological adaptions above those normally expected during high-intensity exercise until there is a significant increase in core temperature (Gonzalez-Alonso et al., 1999). In our study, the measurement of tympanic temperature at the end of each exercise bout (Fig 7.) in the heat can be seen to progressively increase as the players struggle to maintain temperature, which would lead to greater vasodilation and redistribution of blood, contributing to reducing physical capability as the exercise challenged continued.

Summary and Application of Findings These results show the average decrement in mean power output across four bouts of maximal-intensity cycling is similar in heat and hypoxia for a comparable or elevated cardiovascular response. However, the pattern of power degradation over the four sets was dependent upon the environmental condition, with power output impaired sooner in hypoxia compared to exercise in the heat where pronounced reductions in power output only occurred as exercise duration increased. Such profiles of power degradation would indicate that higher mechanical loads are achieved during initial stages of exercise in heat to that of hypoxia and are comparable to those performed in neutral conditions.

Therefore, science / medical practitioners should consider the reason for reducing mechanical load and then select the most appropriate environmental stressor.

The use of heat may have negative implications for severely load comprised players as they are exposed to higher than desirable mechanical stress during the initial stages of exercise whereas hypoxia appears to help safeguard against such an occurrence. In contrast, the more robust player who would benefit from some exposure to higher load may gain more benefit from exercising in the heat to permit higher work outputs but not for the entire session. Additionally, for the player nearing return to performance, repeated exposure to exercise in the heat may act as an ergogenic aid to enhance endurance capabilities in a shorter period of time than can be achieved in hypoxia (Sunderland et al., 2008).

Fig 6. Oxygen saturation in a control condition (C1) and across four exercise bouts when exercising in hypoxia at 13.5% atmospheric oxygen.

Fig 7. Tympanic temperature in a control condition (C1) and across the four exercise bouts when exercising at 40 degrees Celsius.

REFERENCES Garrett AT, Creasy R, Rehrer NJ, Patterson MJ, Cotter JD (2012) Effectiveness of short-term heat acclimation for highly trained athletes. Eur J Appl Physiol,112(5):1827-37.

Goods et al., 2014 Gonzรกlez-Alonso J, Teller C, Andersen SL, Jensen FB, Hyldig T, Nielsen B (1999) Influence of body temperature on the development of fatigue during prolonged exercise in the heat. J Appl Physiol 86(3):10329.

Jubeau M, Rupp T, Temesi J, Perrey S, Wuyam B, Millet GY, Verges S (2016) Neuromuscular Fatigue during Prolonged Exercise in Hypoxia. Med Sci Sports Exerc. 6. [Epub ahead of print] Mackenzie et al., 2016 Mackenzie, B., Wells, C., (2016) Differences in power output profiles during high-intensity intermittent cycling in acute heat and hypoxic exposure. Journal of Sports Sciences, 34: 180 - 181 Sunderland C, Morris JG, Nevill ME (2008) A heat acclimation protocol for team sports. Br J Sports Med, (5):327-33.

Paralikar, S and Paralikar, J (2010) High Altitude Medicine. Indian Journal of Occupational Medicine, 14 (1), 6-12 Vogt M, Hoppeler H (2010) Is hypoxia training good for muscles and exercise performance?

Prog Cardiovasc Dis, 52(6):525-33.

Wells C, Edwards A, Fysh M, Drust B (2014) Effects of high-intensity running training on soccer-specific fitness in professional male players. Appl Physiol Nutr Metab.39(7):763-9.

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