Acute Autonomic and Cognitive Responses to High-Intensity Interval Training With vs. Without a Stroop Task in Male Recreational Athletes

The acute autonomic response to high-intensity interval training (HIIT) is well established, yet it remains unclear whether adding a concurrent cognitive stressor during recovery intervals further perturbs cardiac autonomic control. Sixty-three recreational male young athletes (24.3 ± 4.2 years) were randomly allocated to HIIT (n = 32) or HIIT plus Stroop task (n = 31). Both groups completed 8 × 45 s burpees with 45 s passive recovery; the HIIT plus Stroop task group performed a colour-word Stroop test during recoveries. Pre- and post-exercise assessments included heart-rate variability (HRV) (time/frequency/Poincaré indices), Stroop performance (words, colors, total, interference, estimation), critical flicker fusion threshold, handgrip strength, and horizontal jump. Two-way mixed ANOVAs (Group × Time) tested effects (α = 0.05). Robust time effects emerged in HRV consistent with acute sympathetic activation (↑HR, ↑SI; ↓RR, ↓HRV triangular index in both groups), with small effect sizes; no Group × Time interactions were detected for HRV metrics. For cognition, both groups improved on several Stroop components from pre to post; a main effect of group appeared for the colour’s subtest (F = 5.216, p = 0.029, η² = 0.130), with no interaction. Neuromuscular and arousal measures showed no between-group differences. Adding a Stroop task to HIIT does not further alter acute HRV beyond the effect of HIIT itself, suggesting a ceiling in autonomic perturbation under high physical load. Cognitive work can be integrated during HIIT recoveries without additional autonomic strain, although monitoring of mental fatigue remains advisable.