Rethinking the traditional heat acclimation strategy for Olympic and Paralympic athletes Symposium Introduction Previous Olympic and Paralympic Games have been held in hot, humid conditions that challenge athletes’ ability to thermoregulate and can diminish exercise performance. Heat Acclimation (HA) strategies that use low exercise intensities, of a prolonged, continuous duration and for 10-14 days have traditionally been adopted to prepare athletes for exercise in the heat. While the expected heat stress at the London 2012 Olympic and Paralympic Games may be moderate (~ 21°C/69%rh), recent work by Lorenzo et al., 2010; Journal of Applied Physiology, 109, 1140-1147) and within our own laboratories has demonstrated HA can be beneficial for exercise performance in temperate conditions. Through new evidence however, this symposium will lead the audience to reconsider the traditional ‘one-size-fits-all’ approach when using HA to optimise exercise performance. The merits of short term HA on adaptations and exercise performance will be discussed. The primary stimuli for HA is thought to be a sustained elevation in core temperature of 1-2°C. In practice, traditional HA protocols that apply constant heat stress and exercise intensity over a number of days to elicit adaptations, observe a progressive decline in heat strain over the course of the acclimation period, such that exercise performance in the heat may not be maximized. As part of the introduction to this symposium, data will be presented that compared a progressive HA protocol with a traditional protocol, matched for heat stress on markers of heat adaptation and intermittent sprint exercise in the heat. An important feature of this symposium through the series of scientific presentations, will be to consider the efficacy of variations of the traditional, constant work-rate method and present data that supports the controlled hyperthermia HA technique to achieve a more complete adaptation. Adaptations to HA at a cellular level will also be considered in this symposium. Dr. Neil Maxwell Oral Scientific Paper 1 Effectiveness of dehydration on adaptation to heat This work examined the effectiveness of short-term (5 day) heat acclimation (STHA) with moderately and highly trained athletes; fluid regulatory strain has a thermally-independent role in heat adaptation; and, the impact of STHA on a marker of thermotolerance (inducible heat shock protein 70; HSP70). Ten moderately trained males completed heat acclimation (HA) under controlled hyperthermia (rectal temperature 38.5°C) for 90-min on five consecutive days (Ta = 40°C, 60% RH), on two occasions separated by a five-week washout, in a cross-over design. One HA was undertaken with euhydration (fluid replenishment; EUH) and one with dehydration (no fluid intake; DEH) during daily HA bouts. Participants completed an exercising heat stress test (HST) one week before, then on the 2nd day after HA for both regimes. HST involved cycling at 40% PPO for 90 min (Ta = 35°C, 60% RH), 10 min rest and a ramp protocol (2% PPO each 30 s) to volitional fatigue. On a later occasion eight highly trained male rowers were acclimated under the same protocol but with DEH acclimation only and a rowing-specific HST (2000m rowing performance test). Short-term HA resulted in physiological adaptation and enhanced exercise capacity for moderately trained participants. Compared to EUH permissive DEH during HA bouts conferred larger acclimation-induced increases in resting PV by 4.1% (95%CI: -1.5 to 9.8%; p=0.06), (4.2: 0.7 to 7.8 ml.min-1.100 ml-1; p=0.009), FVC (0.06: 0.02 to 0.10 ml.100ml Tissue-1.min-1.mmHg-1; p=0.006), end-exercise (45.9: 3.6 to 84.4 mL; p=0.02) and decreased end-exercise by 17% (19: -29 to 9 b•min-1; p=0.08). The highly trained athletes had functional heat adaptations of similar magnitude of moderately-trained across DEH acclimation, resting PV expansion (4.5: 0.7 to 8.3%) and increased performance (-4.0: -6.3 to 0.6 s; p=0.02). Plasma total protein-corrected HSP70 increased from rest to end-exercise across acclimation (p=0.001). There was a greater change from rest to end-exercise on day one versus day five HA (p=0.05). In conclusion, short-term (5 day) heat acclimation was effective with adaptations more pronounced after fluid regulatory strain from a dehydration acclimation regime. Similar findings were found using highly trained and lesser-fitness adapted participants. Thermotolerance was increased by dehydration acclimation. Dr Andrew Garrett Oral Scientific Paper 2 Partial heat acclimation of athletes with spinal cord lesion Heat acclimation (HA) can improve thermoregulatory stability in able-bodied athletes in part by an enhanced sweat response. Athletes with spinal cord lesion are unable to sweat below the lesion and it is unknown if they can HA. Five Paralympic shooting athletes with spinal cord lesion completed seven consecutive days HA in hot conditions (33.4 ± 0.6 ºC, 64.8 ± 3.7 %rh) using the thermal clamp method. Aural temperature (Taur) was recorded throughout. Body mass was assessed before and after each session and a sweat collection swab was fixed to T12 of the spine. Fingertip whole blood was sampled at rest on days 1 and 7 for estimation of the change in plasma volume. Resting Taur declined from 36.3 ± 0.2 ºC on day 1 to 36.0 ± 0.2 ºC by day 6 (P < 0.05). During the HA sessions mean Taur declined from 37.2 ± 0.2 ºC on Day 1, to 36.7 ± 0.3 ºC on Day 7 (P < 0.05). Plasma volume increased from day 1 by 1.5 ± 0.6% on day 7 (P < 0.05). No sweat secretion was detected, or changes in body mass observed, from any participant. Despite the limited evaporative heat loss of these athletes partial heat acclimation was achieved. Dr Paul Castle Oral Scientific Paper 3 An alternative method of short term heat acclimation. A period of heat acclimation (HA) reduces the decrement in athletic endurance performance in the heat (Castle et al., 2011; Journal of Sports Sciences 29, 1125-1134). However, the required proximity of HA to competition may compromise training frequency and intensity, cause logistical issues and disrupt tapering for competition. Data from our research group has shown that exertional heat stress (EHS) and exercise induced muscle damage increases rectal temperature (Tre) and Hsp72 and Hsp90α mRNA relative expression in excess of EHS alone (Tuttle et al, 2012; manuscript in preparation). These combined stressors (intervention: 30 mins downhill running (-10%) in 30°C, 50%RH) may convey a form of “crash” HA. Participants completed two bouts (EXB1 & EXB2) of the intervention separated by 1 week to assess the interventions effectiveness with regards to reducing physiological strain and the cellular stress response. The intervention reduced peak rectal temperature in EXB2 by 0.3°C (39.3 ± 0.3°C to 39.0 ± 0.3°C; P = 0.016) and average HR by 5 BPM (154 ± 3 BPM to 149 ± 2 BPM; P = 0.038), compared to EXB1. This reduced physiological strain is comparable to that of short term HA, as shown elsewhere. Further, Hsp72 and Hsp90α mRNA relative expression was attenuated post EXB2 in both leukocytes and vastus lateralis, compared to EXB1, indicating a reduced stress response at a molecular level. Consequently this intervention may be used as an alternative method of partial HA (evidence from both whole body and molecular physiology) in line with recently proposed short term HA models (Garrett et al., 2009; European Journal of Applied Physiology 107, 659-670; Garrett et al., 2012; European Journal of Applied Physiology 112: 1827–1837). Dr Lee Taylor Symposium Conclusions and Discussion The symposium will conclude by outlining the limitations of using traditional heat acclimation methods to optimise exercise performance, discuss alternative approaches and suggest future directions for research. During this time, there will be an opportunity for questions to be asked and the sharing of good practice.
|Publication status||Published - 2012|