Thermal stress and physiological responses in Brazilian jiu-jitsu athletes submitted to simulated fights in a hot environment

Objective: Analyze thermal stress and changes in physiological variables in simulated BJJ fights in a hot environment. Methodology: The study included 12 male athletes, comprising 11 black belts and 1 brown belt. The athletes were divided into pairs according to their categories and there were four 10-minute bouts with 10 minutes of rest between bouts in a covered environment, during the night, with an ambient temperature (TA) of 29.3 ± 0.5ºC and relative air humidity (URA) of 75.9 ± 1.1%. The variables heart rate (HR), lactate, gastrointestinal temperature (Tgi) and skin temperature (Tskin), hand grip, dehydration rate, total sweating and specific urine density were evaluated. HR, lactate and Tgi data were collected before starting the simulated fights (pre 1, 2, 3 and 4), immediately after the end of each fight (post 1, 2, 3, and 4). All other variables were collected during the baseline period, which corresponds to pre 1, and in the post-fight assessments (post-fight 1, 2, 3, and 4). Results: There was a significant reduction in body mass post-fight compared to pre-simulated fights (p < 0.001). Despite ad libitum hydration, athletes transitioned from a euhydrated state to significant-to-severe dehydration by the end of the protocol. HR values were significantly higher post-fight (post 1, 2, 3, 4) compared to rest (pre-1) (p < 0.001). Blood lactate levels increased post-fight (post 1, 2, 3, 4) compared to rest (pre-1). Tgi increased significantly after the first fight (post 1, 2, 3, 4) compared to rest (pre 1) (p < 0.001) and remained stable until the fourth fight. Tskin showed a increase post-fight (post 1, 2, 3) compared to rest (pre-1) (p < 0.001). Conclusions: The thermoregulatory mechanisms were sufficient to maintain thermal control during the simulated BJJ fights.