RESEARCH: Studies reviewed this week: 19 April 2021 to 25 April 2021

HEAT: Exercise under heat stress: thermoregulation, hydration, performance implications and mitigation strategies

A useful review on exercise under heat stress.

A couple of key points from the review:

This review provides a comprehensive and integrative overview of how the human body responds to exercise under heat stress and the countermeasures that can be adopted to enhance aerobic performance under such environmental conditions.
This review also discusses strategies to mitigate the effects of hyperthermia and hypohydration on exercise performance in the heat, by examining the benefits of heat acclimation, cooling strategies and hyperhydration.

PRACTICAL TAKEAWAY - understanding and preparing for hot conditions is important to optimize performance.

NUTRITION: Pre-Exercise Carbohydrate or Protein Ingestion Influences Substrate Oxidation but Not Performance or Hunger Compared with Cycling in the Fasted State

This study investigated the various options for breakfast before exercise. The exercise tests wree performed after eating "a carbohydrate-rich meal (CARB; 1 g/kg CHO), a protein-rich meal (PROTEIN; 0.45 g/kg protein + 0.24 g/kg fat), or water (FASTED)".

The authors showed that:

Fat oxidation was lower for CARB compared with FASTED at and below the VT, and compared with PROTEIN at 60% VT.
Overall, exercising in the overnight-fasted state increased fat oxidation during submaximal exercise compared with exercise following a CHO-rich breakfast, and pre-exercise protein ingestion allowed similarly high levels of fat oxidation.

PRACTICAL TAKEAWAY - if you goal is to increase fat oxidation then exercising in a fasted state or after a protein rich breakfast is better than after a CHO-rich breakfast.

HEAT: Heat acclimation training with intermittent and self-regulated intensity may be used as an alternative to traditional steady state and power-regulated intensity in endurance cyclists

As mentioned in the study above, preparing for performance in the heat is important. This study investigated "the effects of self-regulated and variable intensities sustained during short-term heat acclimation training on cycling performance".

The key findings were that:

Similar improvements in thermal sensation and lower elevations of core temperature in performance following low-intensity heat acclimation (HA-LOW) and high-intensity heat acclimation (HA-HIT) training protocols suggest that high intensity and RPE regulated bouts could be an efficient strategy for short term heat acclimation protocols
The modest impact of lowered thermal sensation on cycling performance confirms that perceptual responses of acclimated athletes are dissociated from physiological stress when exercising in the heat.

PRACTICAL TAKEAWAY - using a polarized and self-regulated approach to training during a short-term heat acclimation protocol appears to be optimal.

LOAD: Stress Biomarkers, Mood States, and Sleep during a Major Competition: “Success” and “Failure” Athlete's Profile of High-Level Swimmers

This study set out to understand the impact of seven days of competition on markers of stress in swimmers. The paper found that there was a significant impact including:

The stress of the competition could trigger a negative mood profile and sleep disturbance which correspond to different responses of biomarkers related to the hypothalamo-pituitary-adrenal axis and the sympathetic nervous system (SNS) activity, cortisol, sAA, and CgA.

PRACTICAL TAKEAWAY - managing stress during a competition period is vital and can affect performance.

LOAD: The quantification of training load, the training response and the effect on performance

I find training load studies fascinating and I've shared a whole range of studies on this topic (all available on the resources page). Most of these studies show that while RPE can be an effective measure of load, it is a challenging variable to quantify in any other way. This review investigated the current research on training load.

The authors suggested that:

To date, no single physiological marker has been identified that can measure the fitness and fatigue responses to exercise or accurately predict performance.
More attention should be directed towards measurements that reflect individual capacity to respond or adapt to exercise training rather than an absolute measure of changes in physiological variables that occur with training.

PRACTICAL TAKEAWAY - closely monitor your athletes (or yourself) to understand how you're adapting to training stress rather than following or using a theoretical model.

HEAT: The effect of medium-term heat acclimation on endurance performance in a temperate environment

Another study on heat acclimation, this time the authors investigated "whether an 11-day heat acclimation programme (HA) enhanced endurance performance in a temperate environment". The two protocols the authors used were:

  • HA consisting of 11 consecutive daily exercise sessions (60–90 min·day−1; n = 16) in a hot environment (40°C, 50% RH) or;
  • (ii) duration and exertion matched exercise in cool conditions (CON; n = 8 [11°C, 60% RH])

The authors concluded that:

11-days HA induces thermophysiological adaptations, but does not alter the key determinants of endurance performance.

PRACTICAL TAKEAWAY - medium-term heat acclimation may improve the sensations during a hot race, but is unlikely to improve performance.

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