Effect of Divergent Solar Radiation Exposure With Outdoor Versus Indoor Training in the Heat: Implications for Performance

O'Connor, FK, Doering, TM, Minett, GM, Reaburn, PR, Bartlett, JD and Coffey, VG. Effect of divergent solar radiation exposure with outdoor versus indoor training in the heat: implications for performance. J Strength Cond Res 36(6): 1622-1628, 2022-The aim of this study was to determine physiological and perceptual responses and performance outcomes when completing high-intensity exercise in outdoor and indoor hot environments with contrasting solar radiation exposure. Seven cyclists and 9 Australian Football League (AFL) players undertook cycling trials in hot conditions (>= 30 degrees C) outdoors and indoors. Cyclists completed 5 x 4 minutes intervals (similar to 80% peak power output [PPO]) with 2 minutes recovery (similar to 40% PPO) before a 20-km self-paced ride. Australian Football League players completed a standardized 20 minutes warm-up (similar to 65% mean 4-minute power output) then 5 x 2 minutes maximal effort intervals. Heart rate (HR), PO, ratings of perceived exertion (RPE), thermal comfort (TC), and thermal sensation (TS) were recorded. Core (T-c) and skin temperature (T-sk) were monitored in cyclists alone. In both studies, ambient temperature, relative humidity, and solar radiation were monitored outdoors and matched for ambient temperature and relative humidity indoors, generating different wet bulb globe temperature (WBGT) for cyclists, but the similar WBGT for AFL players through higher relative humidity indoors. The statistical significance was set at p <= 0.05. Cyclists' HR (p = 0.05), T-c (p = 0.03), and T-sk (p = 0.03) were higher outdoors with variable effects for increased RPE, TS, and TC (d = 0.2-1.3). Power output during intervals was not different between trials, but there were small-moderate improvements in cyclists' PO and 20-km time indoors (d = 0.3-0.6). There was a small effect (d = 0.2) for AFL players' mean PO to increase outdoors for interval 4 alone (p = 0.04); however, overall there were small-moderate effects for lower RPE and TS indoors (d = 0.2-0.5). Indoor training in hot conditions without solar radiation may promote modest reductions in physiological strain and improve performance capacity in well-trained athletes.