Short-term heat training: practically relevant strategies for enhancing team sports performance

Abstract

Repeated exposure to hot and humid conditions is traditionally employed for facilitating physiological and thermoregulatory adaptations that can negate impaired exercise performance in hot conditions. Despite the popularity and interest surrounding heat training, there is currently little practical information for coaches and support staff on how to best implement heat training in a team sport environment. Heat training has the potential to offer accelerated conditioning, rapid physiological and thermal adaptations and the potential to offer performance benefits in temperate environmental conditions. However, the logistical challenges associated with team sports often make implementation of such interventions challenging. The aims of the first experimental study were to enhance endurance running and thermal tolerance using short-term heat training during the pre-season and to evaluate the utility of a novel mixed-mode heat raining intervention in state-level Australian football players. Subsequently, the second study assessed the impact of repeated sprint interval training, with and without brief passive heat exposure on player conditioning and running capacity and its suitability to be integrated with sports-specific training during the competitive season. Therefore, the purpose of this research is to provide coaches and performance staff with pragmatic heat training programs that can be easily applied in the daily training environment without compromising sport-specific objectives. A short-term, intermittent day laboratory-based heat training program was implemented during the pre-season in state-level Australian football players to quantify the degree of fitness benefits and thermal tolerance. Eleven state-level male Australian football players from the same team completed 6 x 60 min sessions (5 min warm up; 5 x 8 min efforts alternating running and cycling; 3 min passive recovery between sets) in HEAT (35°C, 50% RH) and TEMP (temperate; 18°C, 50% Relative Humidity; RH) conditions over 12 days in a counterbalanced crossover design. The crossover design involved two x 12-day training blocks either side of a 4-week washout period ensuring all players completed both HEAT and TEMP training interventions. Running performance pre and post HEAT and TEMP interventions were assessed via the Yo-Yo Intermittent Recovery Test (Level 1), and thermal adaptation using a submaximal (4 x 4 min) treadmill heat stress test (HST) in 35°C, 50% RH. Yo-Yo running distance improved by 9, ±9% in HEAT (standardised mean, ±90% confidence limits) and 13, ±6% in TEMP, however the difference in the mean change between conditions was unclear (0.24, ±0.64 standardised mean, ±90% confidence limits). Regardless of the intervention conditions, there was an order and subsequent training effect indicated by a large 476 ± 168 m increase in running distance between the first and final of the four Yo-Yo tests performed across the study. There was little evidence of thermal adaptation indicated by trivial to small reductions in heart rate, blood lactate, RPE and thermal sensation after both interventions. Differences in mean core and skin temperature between baseline and post-intervention HSTs were unclear. The substantial training effect together with limited thermal adaptation implies that at this point in the season, laboratory-based heat training did not provide additional performance benefits above those obtained by training in temperate conditions. Repeated sprint cycling training with and without brief passive heat exposure was undertaken to evaluate the effects of general conditioning and running capacity in the heat during rounds 16 – 22 of a 22-round state-level Australian football season. Thirty male players in a pre-post parallel group experimental design were assigned to either: Passive + Active Heat (PAH; n=10), Active Heat (AH; n=10) or Temperate (TEMP; n=10) to complete 6 x 40 min repeat effort cycling training sessions (5 min warm up; 6 x 5 x 10 s sprints; 30 s active recovery between sprints and 2 min passive recovery between each set) over 12 days in 35°C (PAH and AH) or 18°C (TEMP) and 50% RH. Players in PAH were exposed to passive heat (seated) for 20 min prior to commencing exercise. Physiological adaptation and running capacity were assessed via a treadmill submaximal HST followed by a time-to-exhaustion test (run capacity) in 35°C, 50% RH. Running capacity increased by 26 ± 8% PAH (0.88, ±0.23; standardised mean, ±90% confidence limits), 29 ± 12% AH (1.23, ±0.45) and 10 ± 11% TEMP (0.45, ±0.48) compared with baseline. There were greater improvements in running capacity for the PAH (0.52, ±0.42; standardised mean, ±90% confidence limits) and AH (0.35, ±0.57) conditions compared to TEMP. However, the difference between AH and TEMP was unclear. Physiological measures assessed during the HSTs were trivial and small, but uncertain following the two heat training interventions. Thus, remained relatively unchanged between baseline and post-intervention testing. In contrast, there were small to moderate reductions in RPE and thermal sensation within AH and also in both AH and PAH compared to TEMP, respectively. When acquiring specific heat adaptation is not a direct priority, 6 x 40 min repeated effort cycling sessions, with and without passive heat exposure are more effective in enhancing running capacity compared to temperate ambient conditions alone in team sport players without interfering with sports-specific training during the season. Modern-day team sports present several challenges that restrict the implementation of traditional heat training practices in a real-world context. When aiming to improve performance in temperate conditions and achieving thermal adaptation is not a direct priority, short duration (<60 min) sessions undertaken intermittently can offer positive conditioning/training effects in a relatively short time frame in both the pre-season and during the season. Similarly, the perceived benefits of undertaking heat training may complement increased training load and underlying physiological/thermal adaptations in facilitating performance benefits in state-level team sport players. Heat training sessions performed every other day to sport-specific training were well tolerated by the players, and can be implemented without disrupting field-based skills sessions or compromising football-specific goals.

Date of Award	2020
Original language	English
Supervisor	Kate PUMPA (Supervisor) & Naroa ETXEBARRIA (Supervisor)