Effects of Intermittent Sprint-Based Heat Acclimation at Various Pedal Resistances on Physiological Responses During Incremental Exercise

Abstract

Purpose

Standard heat acclimation (HA) protocols (low-moderate intensity over a continuous 7–14 days) restore performance and thermoregulation but lack specificity and practicality for intermittent sports athletes. This study compared different pedal resistances in a 3-week intermittent sprint-based HA protocol.

Methods

Fourteen physically active adults were assigned to a sprint pedal resistance training group (TG): 0.075 kg/kg (7.5TG, 6 males, 1 female) or 0.085 kg/kg (8.5TG, 5 males, 2 females). Participants completed baseline incremental time to exhaustion test (TTE), continued with own training for 3 weeks before post-control TTE, then carried out 6 × 15 s cycle sprints with 30 s recovery followed by 30 min low intensity cycling thrice weekly for 3 weeks before completing post-HA TTE test. Testing and HA were completed at 38 °C and 30% relative humidity.

Results

Both groups improved TTE from baseline to post-HA (7.5TG: 9.6% ± 10.8%, 8.5TG: 7.4% ± 3.1%) and post-control to post-HA (7.5TG: 11.0% ± 11.7%, 8.5TG: 6.7% ± 3.9%). Maximal power improved from baseline to post-HA (7.5TG: 293 ± 40 W vs. 321 ± 46 W, 8.5TG: 318 ± 90 W vs. 339 ± 96 W), while only 7.5TG improved maximal power from post-control to post-HA (289 ± 42 W vs. 321 ± 46 W). From baseline to post-HA and post-control to post-HA, only 7.5TG increased time till maximum skin temperature (460 ± 76 s vs. 509 ± 75 s, 461 ± 72 s vs. 509 ± 75 s, respectively) and minimum core-skin gradient (461 ± 71 s vs. 510 ± 74 s, 455 ± 75 s vs. 510 ± 74 s, respectively), while exercising core temperature remained unchanged in both groups. Both groups increased sweat rate (7.5TG: 7.0 ± 3.4 mg/cm²/min vs. 9.6 ± 4.1 mg/cm²/min, 8.5TG: 5.7 ± 3.6 mg/cm²/min vs. 8.3 ± 4.3 mg/cm²/min). Only 7.5TG delayed the onset of blood lactate accumulation from baseline to post-HA (259 ± 126 s vs. 354 ± 86 s).

Conclusion

Intermittent sprint-based HA improves TTE performance and sweat rate while a lighter sprint pedal resistance offers, greater thermal adaptation and fatigue tolerance.

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