Integrating Heat Training in the Rehabilitation Toolbox for the Injured Athlete

Musculoskeletal injuries are arguably one of the most severe impediments athletes may encounter in their career. Depending on the severity of the sustained injury, time-loss could be substantial, leading to profound de-conditioning effects within the cardiovascular, metabolic and muscular systems. For instance, following ACL reconstruction, athletes' return to sport may range between 16 and 52 weeks (Anderson et al., 2019). Case studies in elite soccer players have reported profound losses in whole body fat-free mass (5.8 kg), as well as in lean leg mass (0.9–1.5 kg) following immobilization and inactivity during this period (Milsom et al., 2014; Anderson et al., 2019). Moreover, a 4–20% decline in maximal aerobic capacity (VO2max) has been reported following 2–8 weeks of physical de-conditioning, owing largely to the decline in blood volume, and consequently stroke volume and cardiac output (Mujika and Padilla, 2001). In this context, there is a crucial need to optimize rehabilitation programs, such that the physical demands associated with return to sport and beyond are well-tolerated.

Here we propose that an athlete's rehabilitation program may be optimized by incorporating repeated heat exposures or heat acclimation, given the evidence in support of this modality to minimize skeletal muscle and cardiovascular de-conditioning during periods of disuse and reduced physical activity. For example, there is emerging evidence demonstrating remarkable benefits of heat stress on the regulation of muscle mass (Selsby and Dodd, 2005; Selsby et al., 2007; Ihsan et al., 2014; Hafen et al., 2019). Moreover, training in the heat allows for maintaining a lower absolute work load for a given relative exercise intensity, reducing the mechanical demands of the rehabilitating athlete. While it is important to note that some (Shvartz et al., 1977; Sawka et al., 1985; Lorenzo et al., 2010), but not all (Karlsen et al., 2015; Keiser et al., 2015; Neal et al., 2016) studies have reported improved exercise performance in cooler environments following heat acclimation, harnessing the benefits through passive or active heat acclimation remains a promising strategy to minimize cardiovascular de-conditioning in a rehabilitating athlete, whose training load is considerably reduced. This opinion piece presents how repeated heat exposures may be incorporated in the rehabilitation toolbox at various stages of the return to sport journey (Figure 1).