Abstract
Extreme environmental conditions present athletes with diverse challenges; however, not all sporting events are limited by thermoregulatory parameters. The purpose of this leading article is to identify specific instances where hot environmental conditions either com- promise or augment performance and, where heat accli- mation appears justified, evaluate the effectiveness of pre- event acclimation processes. To identify events likely to be receptive to pre-competition heat adaptation protocols, we clustered and quantified the magnitude of difference in performance of elite athletes competing in International Association of Athletics Federations (IAAF) World
Extreme environmental conditions present athletes with diverse challenges; however, not all sporting events are limited by thermoregulatory parameters. The purpose of this leading article is to identify specific instances where hot environmental conditions either com- promise or augment performance and, where heat accli- mation appears justified, evaluate the effectiveness of pre- event acclimation processes. To identify events likely to be receptive to pre-competition heat adaptation protocols, we clustered and quantified the magnitude of difference in performance of elite athletes competing in International Association of Athletics Federations (IAAF) World
Championships (1999–2011) in hot environments ([25 °C)
with those in cooler temperate conditions (\25 °C). Ath-
letes in endurance events performed worse in hot condi-
tions (*3 % reduction in performance, Cohen’s d [ 0.8;
large impairment), while in contrast, performance in short-
duration sprint events was augmented in the heat compared
with temperate conditions (*1 % improvement, Cohen’s
d [ 0.8; large performance gain). As endurance events
were identified as compromised by the heat, we evaluated
common short-term heat acclimation (B7 days, STHA) and
medium-term heat acclimation (8–14 days, MTHA) pro-
tocols. This process identified beneficial effects of heat
acclimation on performance using both STHA
(2.4 ± 3.5 %) and MTHA protocols (10.2 ± 14.0 %).
These effects were differentially greater for MTHA, which
also demonstrated larger reductions in both endpoint
exercise heart rate (STHA: -3.5 ± 1.8 % vs MTHA:
-7.0 ± 1.9 %) and endpoint core temperature (STHA:
-0.7 ± 0.7 % vs -0.8 ± 0.3 %). It appears that worth-
while acclimation is achievable for endurance athletes via
both short-and medium-length protocols but more is gained
using MTHA. Conversely, it is also conceivable that heat
acclimation may be counterproductive for sprinters. As
high-performance athletes are often time-poor, shorter
duration protocols may be of practical preference for
endurance athletes where satisfactory outcomes can be
achieved.
Introduction
It is popularly perceived that performance in the heat is compromised compared with temperate conditions and that pre-competition adaptation to this environment is a necessity [1, 2]. However, this may not be the case for all events, depending on the intensity and duration of perfor- mance. For elite athletes, there are also issues of time efficiencies to be considered when determining event preparation within busy training and performance sched- ules. Therefore, although some recent articles have added some useful information on this underserved area (e.g., [3, 4]), the purpose of this leading article is to now take this issue forward and describe instances where heat adaptation may be useful, to identify protocols which lead to mean- ingful adaptations and finally to suggest future directions for this important area of research.
Endurance events in particular have often been descri- bed as being compromised in the heat [1, 2]. This effect is most likely mediated as an integrated thermoregulatory response associated with exposure to the heat, including increased exercising heart rate (HR), elevated core (Tc) and skin temperatures, greater perception of effort, thermal strain, thirst, and water loss leading to dehydration (for
It is popularly perceived that performance in the heat is compromised compared with temperate conditions and that pre-competition adaptation to this environment is a necessity [1, 2]. However, this may not be the case for all events, depending on the intensity and duration of perfor- mance. For elite athletes, there are also issues of time efficiencies to be considered when determining event preparation within busy training and performance sched- ules. Therefore, although some recent articles have added some useful information on this underserved area (e.g., [3, 4]), the purpose of this leading article is to now take this issue forward and describe instances where heat adaptation may be useful, to identify protocols which lead to mean- ingful adaptations and finally to suggest future directions for this important area of research.
Endurance events in particular have often been descri- bed as being compromised in the heat [1, 2]. This effect is most likely mediated as an integrated thermoregulatory response associated with exposure to the heat, including increased exercising heart rate (HR), elevated core (Tc) and skin temperatures, greater perception of effort, thermal strain, thirst, and water loss leading to dehydration (for
reviews see [3–5]). It is, therefore, important for athletes to
prepare themselves for events that may take place in
environmentally challenging conditions. This strategy is
particularly important in both team sports [2] and endur-
ance events [6], which require performances to be sus-
tained for extended periods of time potentially increasing
the likelihood of athletes developing substantial dehydra-
tion, overheating or a potentially critical Tc [7]. This sce-
nario often results in fatigue, down-regulation of effort,
performance impairment and, in extreme cases, heat illness
[4–6]. However, particular scenarios where heat-induced
decrements to performance are most prevalent, and the
most effective evidence-based strategies of minimising
these effects, are seldom described.
Almost 50 % of the world’s population now live in the Torrid Zone, close to the Earth’s equator where tempera- tures are hotter and more physically challenging than in the Temperate or Frigid Zones [8]. Consequently, many major sporting events are now scheduled to be held in geo- graphical locations that experience hot and humid envi- ronmental conditions. These locations include the 2015 International Association of Athletics Federations (IAAF) World Championships (Beijing, summer), the 2016 Olympic Games (Brazil, summer), and the 2022 Fe ́de ́ration Internationale de Football Association (FIFA) World Cup (Qatar). It is, therefore, critical that competitive athletes are adequately prepared for such competitions, particularly individuals more used to living and exercising in temperate environments and unaccustomed to hot conditions. For athletes not living and regularly training in the Torrid Zone, most would likely require some form of preparatory heat training prior to embarking on competition in this region. It is often reported that 10–14 days of heat expo- sure [3] is ample heat acclimation; however, these exten- ded interventions might not be viable for most sporting programmes. This period may be particularly challenging for time-poor high-performance athletes in terms of avail- ability, timing, training and/or logistical reasons. To com- bat this, there have been recent efforts to evaluate the effectiveness of shorter heat training programmes of 7 days or shorter duration [4, 5]. The priority for coaches and athletes in such cases is determining the minimum number of days of heat training needed to provide some benefit, within their busy training and performance schedules.
Both short- and medium-term heat adaptation protocols can elicit changes in important physiological parameters such as plasma volume (PV) expansion, reductions to exercising HR, Tc, and sweating commences at a lower Tc with a more dilute concentration of metabolites [9], which could be useful for subsequent performances in the heat and also in cool conditions where potential fluid loss is substantial [10]. It is important to understand how these physiological changes occur, and the potential effects they have on athletes’ performances. For example, an expansion of PV can promote improved performance in aerobic events, most likely by reducing plasma protein loss [11, 12] and increasing blood volume, thus mediating a decreased exercising HR in the heat through adaptive gains in central venous return and preload [4, 13, 14]. Consequently, an increase to stroke volume mediated by gains in PV and blood volume lowers cardiac frequency [15, 16]. As heat adaptation increases PV, the body more effectively regu- lates blood pressure in the face of fluid loss as a conse- quence of increased levels of sweat [17]. Collectively these adaptations lower HR, promote reduced thermal strain and more efficient transfer of heat [17]. Therefore, as PV expansion plays an important role in extending endurance exercise performance, heat training programmes promoting greater PV expansion are of benefit. Nevertheless, this adaptive response may only be of relevance for athletes undertaking endurance events, where fluid loss and heat dissipation mechanisms play a meaningful role in race or competition performance. For example, athletes competing in events that require only short bursts of anaerobic power (e.g., 100 m sprint) are unlikely to experience a decrement in performance in hot conditions as they are under sub- stantially less sustained thermal load compared with their endurance counterparts.
Brief analysis of performances identified that the tem-
perate conditions (\25 °C) resulted in faster performances
in endurance events ([5,000 m) (*2 % mean gain, med-
ium effect) (Fig. 1; Table 1). Conversely, the sprint events
(B200 m) demonstrated the opposite effect with athletes
performing better in hot conditions (*2 % mean gain,
medium to large effect) compared with the events in
temperate climates. As might be expected, middle-distance
events were less affected by ambient conditions and con-
siderable variation between performance gains and losses
were observed for males and females, probably due to the
influence of other factors such as race tactics (Fig. 1).
Almost 50 % of the world’s population now live in the Torrid Zone, close to the Earth’s equator where tempera- tures are hotter and more physically challenging than in the Temperate or Frigid Zones [8]. Consequently, many major sporting events are now scheduled to be held in geo- graphical locations that experience hot and humid envi- ronmental conditions. These locations include the 2015 International Association of Athletics Federations (IAAF) World Championships (Beijing, summer), the 2016 Olympic Games (Brazil, summer), and the 2022 Fe ́de ́ration Internationale de Football Association (FIFA) World Cup (Qatar). It is, therefore, critical that competitive athletes are adequately prepared for such competitions, particularly individuals more used to living and exercising in temperate environments and unaccustomed to hot conditions. For athletes not living and regularly training in the Torrid Zone, most would likely require some form of preparatory heat training prior to embarking on competition in this region. It is often reported that 10–14 days of heat expo- sure [3] is ample heat acclimation; however, these exten- ded interventions might not be viable for most sporting programmes. This period may be particularly challenging for time-poor high-performance athletes in terms of avail- ability, timing, training and/or logistical reasons. To com- bat this, there have been recent efforts to evaluate the effectiveness of shorter heat training programmes of 7 days or shorter duration [4, 5]. The priority for coaches and athletes in such cases is determining the minimum number of days of heat training needed to provide some benefit, within their busy training and performance schedules.
Both short- and medium-term heat adaptation protocols can elicit changes in important physiological parameters such as plasma volume (PV) expansion, reductions to exercising HR, Tc, and sweating commences at a lower Tc with a more dilute concentration of metabolites [9], which could be useful for subsequent performances in the heat and also in cool conditions where potential fluid loss is substantial [10]. It is important to understand how these physiological changes occur, and the potential effects they have on athletes’ performances. For example, an expansion of PV can promote improved performance in aerobic events, most likely by reducing plasma protein loss [11, 12] and increasing blood volume, thus mediating a decreased exercising HR in the heat through adaptive gains in central venous return and preload [4, 13, 14]. Consequently, an increase to stroke volume mediated by gains in PV and blood volume lowers cardiac frequency [15, 16]. As heat adaptation increases PV, the body more effectively regu- lates blood pressure in the face of fluid loss as a conse- quence of increased levels of sweat [17]. Collectively these adaptations lower HR, promote reduced thermal strain and more efficient transfer of heat [17]. Therefore, as PV expansion plays an important role in extending endurance exercise performance, heat training programmes promoting greater PV expansion are of benefit. Nevertheless, this adaptive response may only be of relevance for athletes undertaking endurance events, where fluid loss and heat dissipation mechanisms play a meaningful role in race or competition performance. For example, athletes competing in events that require only short bursts of anaerobic power (e.g., 100 m sprint) are unlikely to experience a decrement in performance in hot conditions as they are under sub- stantially less sustained thermal load compared with their endurance counterparts.
Comparison of Running Performances in Hot
and Temperate Conditions: IAAF Track and Field Performances (1999–2011)
Numerous studies have examined the effects of environ- mental conditions on performance in controlled isolated laboratory experiments. However, to fully ascertain whe- ther or not environmental conditions influence elite field- based performance, it is useful to consider the magnitude of change in outcomes of regularly scheduled events over a longitudinal period performed in different conditions. This type of analysis can be performed by examining secondary data from scheduled major events such as those organised by the IAAF. These data are publicly available and facil- itate rapid and meaningful comparisons when appropriately clustered for analysis of data trends. To address the ques- tion of where and which events are most affected by environmental conditions, we collated and analysed the mean of the top ten performances in distance events (top 60 % of track events) and top six performances in sprint performances (top 60 %) for males and females in the 100, 200, 400, 800, 1,500, 5,000, 10,000 m and marathon events from seven consecutive IAAF World Championships (1999–2011). Events were categorised as either temperate (n = 41) or hot (n = 44) conditions, separated using a standardised threshold temperature of 25 °C as an index of
and Temperate Conditions: IAAF Track and Field Performances (1999–2011)
Numerous studies have examined the effects of environ- mental conditions on performance in controlled isolated laboratory experiments. However, to fully ascertain whe- ther or not environmental conditions influence elite field- based performance, it is useful to consider the magnitude of change in outcomes of regularly scheduled events over a longitudinal period performed in different conditions. This type of analysis can be performed by examining secondary data from scheduled major events such as those organised by the IAAF. These data are publicly available and facil- itate rapid and meaningful comparisons when appropriately clustered for analysis of data trends. To address the ques- tion of where and which events are most affected by environmental conditions, we collated and analysed the mean of the top ten performances in distance events (top 60 % of track events) and top six performances in sprint performances (top 60 %) for males and females in the 100, 200, 400, 800, 1,500, 5,000, 10,000 m and marathon events from seven consecutive IAAF World Championships (1999–2011). Events were categorised as either temperate (n = 41) or hot (n = 44) conditions, separated using a standardised threshold temperature of 25 °C as an index of
comfortable working temperature [18]. It was determined
to utilise 25 °C as it further represented the full cohort
(n = 85) mean temperature (24.5 °C) and resulted in a
temperate condition mean ± SD of 18.5 ± 3.2 °C
(humidity 59.6 ± 7.0 %) and a hot condition mean ± SD
temperature of 30 ± 4.3 °C; (humidity 61.3 ± 4.9 %),
which are both in range of common specifications for these
conditions. Although 25 °C is a relatively high threshold
temperature, outdoor exercise benefits to a greater extent
from convective cooling than laboratory exercise, meaning
a higher temperature is more comfortable outdoors [19].
Therefore, we sought to recognise this in contrast to lab-
oratory exercise [20].
The marathon exhibited the largest performance
impairment in the heat, with a mean reduction of 3.1 % for
males (also a large effect; effect size [ES] = -2.0) and
2.7 % mean change for females (large effect; ES = -2.4)
(Table 1). Although inferences from this observation were
limited due to absence of knowledge in relation to race
tactics, it is most likely that these reductions in perfor-
mance were primarily related to the ambient temperature
and absolute humidity in which the athletes were
competing.
There are logical physiological and behavioural expla- nations for the differential effects of environment on per- formance variations in endurance and sprint events which have been detailed previously [8]. However, the underlying observation that hot conditions do not necessarily com- promise all events is an important consideration for athletes and coaches in their preparation for competition based in the heat. This information should be useful for evidence- based decisions on prescribing appropriate pre-event acclimation for endurance-type activities where perfor- mance is most likely to be impeded in the heat.
Defining the optimum length of a heat acclimation protocol
will be influenced by two factors: first, in physiological
performance terms, the number of sessions needed to attain
appropriate adaptations, and, second, the practical issues of
logistics related to the competition such as a one-off
tournament or an ongoing seasonal competition combined
with player availability. Research has primarily focused on
the acute effects in response to a single stressor, or in preparation for a one-off event, with little practical rec-
ognition of preparatory time restrictions commonly expe-
rienced by athletes across a competitive season. In most
sports, teams and athletes need to compete in various
conditions across a season, and hot condition events might
only constitute a short period within the competitive cycle
[21]. As such, it is important to consider both the acute
effects of acclimation and secondary (residual) factors
which might influence the magnitude and time course of
benefits.
There are logical physiological and behavioural expla- nations for the differential effects of environment on per- formance variations in endurance and sprint events which have been detailed previously [8]. However, the underlying observation that hot conditions do not necessarily com- promise all events is an important consideration for athletes and coaches in their preparation for competition based in the heat. This information should be useful for evidence- based decisions on prescribing appropriate pre-event acclimation for endurance-type activities where perfor- mance is most likely to be impeded in the heat.
Comparison of Short- and Medium-Term Heat
Acclimation Models
The majority of heat acclimation research to date has
examined either short-term heat acclimation (B7 days,
STHA) (Table 2), or medium-term heat acclimation
(8–14 days, MTHA) (Table 3) protocols. Clearly, for elite
athletes performing in a congested competitive season, a
shorter acclimation period would be advantageous and less
disruptive to routine training. Therefore, we have made a
brief practical comparative analysis to identify the degree
of benefit derived from both STHA and MTHA protocols
[21]. A representative sample of relevant research papers
were included on the basis of acclimation or acclimatisa-
tion occurring in conjunction with exercise as well as the
reporting of either a performance variable such as a time
trial or time to exhaustion, HR, Tc or PV. From these data,
pooled percentage change (mean ± 90 % confidence limits
[CL]) as well as ES size was calculated.
From this brief comparison of available data, it is evi- dent that there are merits to both STHA and MTHA strategies. Both strategies appear to result in some positive effects on subsequent performance outcome, HR adapta- tions, and reductions to exercising Tc (Table 2). However, it is also evident that MTHA protocols are more beneficial for eliciting plasma volume expansion (*7 % mean gain) when compared with STHA (*3.5% mean gain) (Tables 2, 3, 4). This is also supported by changes in performance outcomes which demonstrate greater gains in response to MTHA compared with STHA protocols. The extent of any possible gain will be acutely meaningful among high-performance athletes for whom the smallest advantage represents a competitive edge (Table 4). It is plausible that elite athletes may also adapt more rapidly to a hot environment and several studies [2, 4] indicate short- term protocols are capable of evoking beneficial adapta- tions to athletic performance, but greater consistency of protocol design and a considerably larger volume of data is required to fully elucidate this area of athletic preparation. The balance between time effectiveness of the protocol and gaining meaningful adaptation should be the focus of future investigations. Nevertheless, it is important for a leading article such as this to identify important current deficiencies in contemporary practice and research litera- ture, and propose areas in which more empirical data is required.
Based on current evidence and utilising a limited range of protocols, MTHA acclimation periods (8–14 days) are of more benefit for both performance and physiological indices such as PV expansion, lower exercising Tc, and lower end-point exercise HR. These observations are likely to be particularly meaningful for the preparation of athletes competing in particularly long duration events such as marathon or triathlon, which would be most challenging to heat dissipation mechanisms, or athletes required to con- tinue with high-quality training regimens with minimal disruption. For example, hot environmental conditions may diminish training intensity among non-acclimated athletes if they are still acclimating, which could induce a detraining effect. Therefore, the individualised require- ments and periodisation of athletic preparation must be carefully considered.
Although it has been reported that, following heat
acclimation, physiological adaptations may decay after a exposure, although there is currently no systematic evi-
dence of this type of strategy being performed. Routine and
regular exposure to heat during an acclimation protocol
enables the athlete to experience the heat in day-to-day
training sessions [17], and athletes can gradually increase
passive heat exposure related to daily living as soon as
possible (i.e., live hot). Greater research in this area and
manipulations of time spent training and passively recov-
ering in hot or cool conditions may help ascertain whether
residual effects of heat exposure are retained and, once
undertaken, whether and how often it should be repeated.
From this brief comparison of available data, it is evi- dent that there are merits to both STHA and MTHA strategies. Both strategies appear to result in some positive effects on subsequent performance outcome, HR adapta- tions, and reductions to exercising Tc (Table 2). However, it is also evident that MTHA protocols are more beneficial for eliciting plasma volume expansion (*7 % mean gain) when compared with STHA (*3.5% mean gain) (Tables 2, 3, 4). This is also supported by changes in performance outcomes which demonstrate greater gains in response to MTHA compared with STHA protocols. The extent of any possible gain will be acutely meaningful among high-performance athletes for whom the smallest advantage represents a competitive edge (Table 4). It is plausible that elite athletes may also adapt more rapidly to a hot environment and several studies [2, 4] indicate short- term protocols are capable of evoking beneficial adapta- tions to athletic performance, but greater consistency of protocol design and a considerably larger volume of data is required to fully elucidate this area of athletic preparation. The balance between time effectiveness of the protocol and gaining meaningful adaptation should be the focus of future investigations. Nevertheless, it is important for a leading article such as this to identify important current deficiencies in contemporary practice and research litera- ture, and propose areas in which more empirical data is required.
Based on current evidence and utilising a limited range of protocols, MTHA acclimation periods (8–14 days) are of more benefit for both performance and physiological indices such as PV expansion, lower exercising Tc, and lower end-point exercise HR. These observations are likely to be particularly meaningful for the preparation of athletes competing in particularly long duration events such as marathon or triathlon, which would be most challenging to heat dissipation mechanisms, or athletes required to con- tinue with high-quality training regimens with minimal disruption. For example, hot environmental conditions may diminish training intensity among non-acclimated athletes if they are still acclimating, which could induce a detraining effect. Therefore, the individualised require- ments and periodisation of athletic preparation must be carefully considered.
Preparatory Activities that may Optimise Exercise
in the Heat
It is often purported that, for exercise-induced heat accli- mation to be most effective, athletes should employ the
It is often purported that, for exercise-induced heat accli- mation to be most effective, athletes should employ the
same exercise mode in which they will compete [17]. One
way to achieve this is to use high-specification ergometry
in a regulated hot and/or humid environment in a sealed
heat chamber, utilising the athlete’s common exercise
modality. Depending on the expected environmental con-
ditions of the targeted athletic event, mere heat exposure in
the absence of (elevated) humidity is less appropriate for
preparation for hot humid environments [22]. Specific
humidity exposure can form part of the acclimation strat-
egy if appropriate for the athlete, as high humidity is an
aspect of heat exposure that is both extremely challenging
and under researched [22]. Responsiveness to these con-
ditions requires manipulation of training volume and
intensity to ensure that the appropriate exercise and
recovery strategies are applied. Quantifying the degree of
thermal load throughout training sessions through devices
such as ingestible Tc pills can complement this process.
Simple submaximal heat stress tests that include physio-
logical and performance measures can be used throughout
the acclimation process to indicate the level of adaptation
reached [23].
It is possible that to adapt to the heat optimally and in a
time efficient way, short-term protocols may best utilise a
combination of active acclimation and passive acclimati-
sation. This could be achieved by using widely reported
and effective heat tolerance training protocols in stand-
ardised conditions (acclimation), but also by promoting
passive effects of the heat by living in hot conditions over
the short- or medium-term period (acclimatisation). Living
in the heat could enable athletes to adapt to hot conditions
more rapidly while facilitating training in the cooler parts
of the day. It has also recently been proposed that heat
training may prove a useful preparatory strategy for per-
formance in cool and temperate conditions [10], and con-
sequently the potential gains from STHA and MTHA could
be multi-faceted. Therefore, a combined approach could
prove effective and achievable in short-duration protocols
(\7 days); however, new research is required to clarify the
interactions between STHA and MTHA and the extent to
which passive exposure to heat might be useful.
Training intensities in hot or humid conditions, cer- tainly in the short term, should not rely solely on HR or personal best times as effective markers of adaptation as these can be misleading [25]. Consequently, the use of scalar methods such as perceived exertion may be more effective in this context. Effective pacing strategies take time to establish in the heat and athletes should expect a degree of performance decrement in events of prolonged duration, especially when still acclimating. Knowing that elite athletic performance can be reduced by as much as 3 % in endurance events such as the marathon (Table 1), athletes can adjust their pacing strategies to ensure max- imum possible performance, taking into consideration their current level of acclimation, relevant ambient con- ditions (temperature and humidity) and other competitor actions. It seems likely that the shorter time spent accli- mating, the faster the acquired adaptations may diminish [8] and, therefore, it is probable that undertaking pre-event acclimation, top-up sessions, and living hot as soon as practical could facilitate athletes to compete at greater intensities in hot and humid conditions [26]. Potentially, the combination of all three strategies (heat acclimation, top-up sessions and living hot) may yield greater
Training intensities in hot or humid conditions, cer- tainly in the short term, should not rely solely on HR or personal best times as effective markers of adaptation as these can be misleading [25]. Consequently, the use of scalar methods such as perceived exertion may be more effective in this context. Effective pacing strategies take time to establish in the heat and athletes should expect a degree of performance decrement in events of prolonged duration, especially when still acclimating. Knowing that elite athletic performance can be reduced by as much as 3 % in endurance events such as the marathon (Table 1), athletes can adjust their pacing strategies to ensure max- imum possible performance, taking into consideration their current level of acclimation, relevant ambient con- ditions (temperature and humidity) and other competitor actions. It seems likely that the shorter time spent accli- mating, the faster the acquired adaptations may diminish [8] and, therefore, it is probable that undertaking pre-event acclimation, top-up sessions, and living hot as soon as practical could facilitate athletes to compete at greater intensities in hot and humid conditions [26]. Potentially, the combination of all three strategies (heat acclimation, top-up sessions and living hot) may yield greater
improvements in performance but this premise remains to
be tested and may be best suited to either individual sports
or tournament-like competitions that are major features of
the athletes’ season.
The adaptations underpinning maintenance of perfor- mance are likely consequent to the cumulative effect of the necessary heat adaptations for that particular individual or event. As discussed above, a 100 m runner may not require a lowered HR or Tc or other body cooling capabilities for optimal performance. It is plausible that physiological factors associated with being non-acclimated to the heat, such as peripheral vasodilation, coupled with elevated pre- race muscle temperatures may actually be beneficial in the context of sprinting performance although this is a concept rarely considered [27]. Minimising heat acclimation adaptations for these athletes could, therefore, be of benefit as it is possible that acclimation could have the opposite of the intended effect. More data are required to determine if it could be counter-productive for sprint athletes to undertake heat acclimation. It is even conceivable that sprinters may gain more from exaggerating the effects of initial heat exposure by undertaking pre-(hot)event cold acclimation to promote immediate ‘fight or flight’ style of responsiveness to the heat so as to up-regulate muscle temperature, elevate HR and Tc as a means of readiness for very short duration events [28]. It is one of the purposes of a leading article to challenge existing concepts and stim- ulate new research; it is our view that new research is required to clarify the issues we have identified.
Conclusion
Athletic performance for males and females participating in endurance events is likely to be impaired in very warm to hot environments. The opposite is the case for athletes competing in short-distance sprint events. Short-term heat acclimation programmes of \7 days provide athletes with modest thermoregulatory adaptations and performance benefits but, based on current evidence, more can be gained from medium-term ([8–14 days) acclimation periods. However, considerable recent evidence suggests STHA may be worthwhile [5] as, given the practical consider- ations of congested training and competition schedules, coaches and athletes will most likely give preference to shorter-term protocols. More efficient shorter-term accli- mation may be achieved through strategies such as manipulations of active and passive periods of heat expo- sure and top-up sessions over the adaptive period.
The adaptations underpinning maintenance of perfor- mance are likely consequent to the cumulative effect of the necessary heat adaptations for that particular individual or event. As discussed above, a 100 m runner may not require a lowered HR or Tc or other body cooling capabilities for optimal performance. It is plausible that physiological factors associated with being non-acclimated to the heat, such as peripheral vasodilation, coupled with elevated pre- race muscle temperatures may actually be beneficial in the context of sprinting performance although this is a concept rarely considered [27]. Minimising heat acclimation adaptations for these athletes could, therefore, be of benefit as it is possible that acclimation could have the opposite of the intended effect. More data are required to determine if it could be counter-productive for sprint athletes to undertake heat acclimation. It is even conceivable that sprinters may gain more from exaggerating the effects of initial heat exposure by undertaking pre-(hot)event cold acclimation to promote immediate ‘fight or flight’ style of responsiveness to the heat so as to up-regulate muscle temperature, elevate HR and Tc as a means of readiness for very short duration events [28]. It is one of the purposes of a leading article to challenge existing concepts and stim- ulate new research; it is our view that new research is required to clarify the issues we have identified.
Conclusion
Athletic performance for males and females participating in endurance events is likely to be impaired in very warm to hot environments. The opposite is the case for athletes competing in short-distance sprint events. Short-term heat acclimation programmes of \7 days provide athletes with modest thermoregulatory adaptations and performance benefits but, based on current evidence, more can be gained from medium-term ([8–14 days) acclimation periods. However, considerable recent evidence suggests STHA may be worthwhile [5] as, given the practical consider- ations of congested training and competition schedules, coaches and athletes will most likely give preference to shorter-term protocols. More efficient shorter-term accli- mation may be achieved through strategies such as manipulations of active and passive periods of heat expo- sure and top-up sessions over the adaptive period.
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