• Adolescent
• Sweating
• Environment
• Heat
• Sports

Good youth sports coaches know well the routine leading up to the early stages of a new season. Assess every child carefully, while identifying and then prioritising the particular gaps and needs, and next outline an approach and plan to effectively advance the process of individual talent and sport development in a positive and enjoyable learning environment, in an effort to make the most of each one's athletic potential and move closer to his or her personal sport aspirations. The coach then begins to work through progressive training and development sessions with each youth athlete and introduces appropriate complementary physical conditioning, while continuing to refine technique and develop viable new competitive tactics. The competition schedule is then carefully planned and the season begins. However, for many young athletes, especially those participating in summer outdoor individual or team sports, environmental heat stress—particularly when the humidity level is high—can have an unanticipated overriding negative impact that can readily undo advances in fitness, movement, speed, power, endurance and competition tactics and goals.

There is widespread recognition of and emphasis (including in the featured consensus statement)1 on the challenges to a young athlete's well-being, safety and sport performance when training and competing in the heat. Moreover, the contributing roles of the environment, acclimatisation status, hydration and other training or competition conditions and scenarios on mitigating or exacerbating exertional heat illness risk have been well clarified. Accordingly, recognised policy statements and guidelines on training and competing in the heat have placed an appropriate emphasis on addressing modifiable factors to meaningfully assist in keeping youth athletes safe and performing well in hot weather.2–4 Yet, undue heat-related problems continue across all sports when youth athletes train and compete in outdoor hot-weather venues. Unfortunately, the response is too often reactionary versus informed anticipation and prevention—that is, parents and coaches usually seek help after a significant problem repeatedly occurred which ultimately cost an important game, match, championship or even sometimes a young athlete's life.

There had been a longstanding perspective that children are less effective in regulating body temperature, incur greater cardiovascular and thermal strain during strenuous physical activity in the heat and thus have lower exercise-heat tolerance compared with adults. This view was based on early studies showing maturational differences emphasising a lower sweating rate, greater body surface area-to-mass ratio (BSA/M), higher metabolic rate during exercise (lower exercise economy) and a purported lower cardiac output for a given level of exercise in children.5–10 However, closer examination indicates that muscle efficiency is not influenced by biological maturation, adult–child differences in exercise economy disappear with equal relative exercise intensity, cardiac responses are similar and equally effective in prepubertal and mature participants and any potential disadvantage related to BSA/M and greater heat gain from the environment would be a comparable liability for children only in extreme heat conditions.11 Importantly, minor variability and differences in net metabolic heat production in children compared with adults are offset by higher levels of relative (to body mass) evaporative cooling and sweating efficiency, thus yielding lower mass-dependent heat storage.12 Accordingly, the contemporary perspective is that adequately hydrated and heat-acclimatised youth athletes are not at a distinguishing cardiovascular or thermoregulatory disadvantage compared to similarly fit, hydrated and acclimatised adults during exercise in the heat. This is not to say that environmental heat stress is benign to youth; but, it is clear, just as with adults, that careful planning and preparation and beginning a bout of training or competition in a well-rested and adequately hydrated, nourished and acclimatised state can effectively extend the range of exercise-heat tolerance for healthy young athletes and minimise the negative effects on sport performance and well-being.13 However, with the transition from early childhood through late adolescence, athletes, parents, coaches and event administrators need to be cognisant of and suitably accommodate the greater sweat losses and potential increases in thermal strain and exertional heat illness risk that accompany physical growth, maturation and enhanced fitness and athletic/sport skill.

As a youth athlete grows, physically develops and matures, more heat is produced from a greater muscle mass and more mature sweat glands appropriately fulfil their increased sweat production capacity during vigorous physical activity, resulting in a greater thermal load and an increase in sweat fluid and electrolyte (primarily sodium) losses, respectively. Unlike as in a young child or early adolescent, total body water and exchangeable sodium deficits, resulting from extensive sweating during a single training session, game, match or race, can be comparatively more substantial in a mid-teen to late-teen athlete.14 These sizable deficits and sometimes greater levels of thermal strain are more likely to negatively affect performance and increase the risk for incurring exertional heat illness in the ongoing bout of activity or the next one, if adequate measures are not taken and/or there is insufficient time to offset these greater challenges and aptly recover.15–19 Moreover, longer hard workouts and contests that are often characteristic with more physically developed, fit and skilled older adolescent athletes can result in greater levels of muscle damage and a potential carry-over effect that could increase thermal strain during the next training session or contest.20 Parents and coaches often grumble, for example—“She/he never had these problems in the heat as a 12-year-old!” This is often a case of not recognising and fully appreciating the naturally occurring progressive changes in metabolic heat production and sweating with growth, maturation and physical development through adolescence to young adulthood and the greater consequent requirement for more intentional and precise offsetting measures. Coaches need to adjust workouts and parents and coaches need to be mindful of and, at times, alter the competition loads and always firmly emphasise proper recovery in response to the heat for all age groups in youth sports; however, they need to be particularly mindful of the progressively greater challenges as a young athlete gets older and trains and competes at a higher level. This might seem obvious and seemingly should be naturally accommodated by inherent behavioral changes (eg, self-prompted more deliberate and aggressive rehydration) by the athlete—but these greater hydration and recovery challenges are often not sufficiently managed until problems are encountered, individualised needs are determined and more specific offsetting strategies are effectively implemented.