Effectiveness of short-term heat acclimation on intermittent exercise in thermoneutral and hot environments

It is well-established that repetition of heat stress exposure has been shown to facilitate adaptations to the heat but these protocols have tended to be of a fixed work intensity, continuous exercise, long-term in duration (>7 days) and use hydration. Secondly, there is limited information on the potential use of heat acclimation as a training method for human performance in thermoneutral conditions. Therefore, the aims of this study were to investigate the effectiveness of short-term heat acclimation (STHA) for 5 days, using the controlled hyperthermia technique with dehydration, on intermittent exercise in thermoneutral and hot environments

Effectiveness of Short-Term Heat Acclimation on Intermittent Sprint Performance in the Heat with Moderately Trained Males

Purpose: Effectiveness of short-term heat acclimation (STHA), over 5-days (permissive dehydration), on intermittent heat stress test (HST) with males. Methods: Ten, moderately-trained, males (mean [SD]; age 25.6 [8.9] y; stature 180.7 [5.6] cm; body mass 83.2 [10.8] kg; and 45.3 [6.5] mL.kg-1.min-1) participated. The HST was 9 x 5min (45-min) of intermittent exercise based on professional soccer players. One week apart, HST1 vs HST (11.0°C; 50%RH), as a reliability trial and HST3 in 31.0°C; 50%RH were completed. Then 90 min dehydration, STHA (no fluid intake), for 5 consecutive days (39.5oC; 60%RH), using controlled-hyperthermia (~rectal temperature [Tre] 38.5oC). The HST4 within one week after STHA. Blood plasma constituents: percent plasma volume (%PV), aldosterone, total protein, albumin, electrolytes, cortisol and HSP70. Data analysis reported as mean differences with 95% confidence intervals (95%CI) and Cohen’s d effect size. Results: Post STHA, there was a decrease of -0.20 Tre at 45-min in the HST (95%CI -0.40 to -0.05°C; P=0.03; d =-0.56); mean skin temperature (-0.80; -1.30 to -0.30°C; P=0.007; d =-1.46) and mean body temperature (-0.30; -0.50 to -0.10°C, P=0.01; d =-0.75). Cardiac frequency reduced (-3: -5 to -1 b.min-1; P=0.01; d =-0.20) and %PV increased (7.3: 0.9 to 13.7%; P=0.03; d=0.59). Mean Peak Power (MPO) increased (Pd =0.63). Conclusions: Short-term heat acclimation (5-days) with dehydration, using controlled-hyperthermia technique, is effective for physiological adaptations during intermittent exercise in the heat, with moderately trained males

Effectiveness of short-term heat acclimation on intermittent sprint performance in the heat with moderately trained males.

Introduction: Effectiveness of short-term heat acclimation (STHA), over 5-days (permissive dehydration), on intermittent heat stress test (HST) with males. Methods: Ten, moderately-trained, males (mean [SD]; age 25.6 [8.9] y; stature 180.7 [5.6] cm; body mass 83.2 [10.8] kg; and 45.3 [6.5] mL.kg-1.min-1) participated. The HST was 9 x 5min (45-min) of intermittent exercise based on professional soccer players. One week apart, HST1 vs HST (11.0°C; 50%RH), as a reliability trial and HST3 in 31.0°C; 50%RH were completed. Then 90 min dehydration, STHA (no fluid intake), for 5 consecutive days (39.5oC; 60%RH), using controlled-hyperthermia (~rectal temperature [Tre] 38.5oC). The HST4 within one week after STHA. Blood plasma constituents: percent plasma volume (%PV), aldosterone, total protein, albumin, electrolytes, cortisol and HSP70. Data analysis reported as mean differences with 95% confidence intervals (95%CI) and Cohen’s d effect size. Results: Post STHA, there was a decrease of -0.20 Tre at 45-min in the HST (95%CI -0.40 to -0.05°C; P=0.03; d =-0.56); mean skin temperature (-0.80; -1.30 to -0.30°C; P=0.007; d =-1.46) and mean body temperature (-0.30; -0.50 to -0.10°C, P=0.01; d =-0.75). Cardiac frequency reduced (-3: -5 to -1 b.min-1; P=0.01; d =-0.20) and %PV increased (7.3: 0.9 to 13.7%; P=0.03; d=0.59). Mean Peak Power (MPO) increased (P<0.05) across sprints 7, 8 and 9. Time to exhaustion increased (167: -15 to 350 s; P=0.06; d =0.63). Conclusions: Short-term heat acclimation (5-days) with dehydration, using controlled-hyperthermia technique, is effective for physiological adaptations during intermittent exercise in the heat, with moderately-trained males