Bout duration in high-intensity interval exercise modifies hematologic, metabolic and antioxidant responses.

OBJECTIVE

This study compared hematologic, metabolic and antioxidant responses between three high-intensity interval exercise (HIIE) trials of different bout duration and a continuous exercise trial (CON), all with equal average intensity, total work, and duration.

METHODS

Eleven healthy young males performed four trials involving 20 min of cycling, either continuously (49% of power at VOmax, PPO), or intermittently with 48 10-s bouts (HIIE10), 16 30-s bouts (HIIE30) or 8 60-s bouts (HIIE60) at 100% PPO, with a 1:1.5 work-to-recovery ratio at 15% PPO. Venous blood was obtained before, immediately after, and 1 h post-exercise to evaluate hematologic, metabolic and antioxidant responses. Blood lactate concentration was measured in capillary blood during exercise, while urine lactate was measured before and 1 h post-exercise.

RESULTS

Post-exercise leukocyte count (mean ± SD; 9.7 ± 2.8 k μL), uric acid concentration (0.35 ± 0.10 mmol L), glucose concentration (6.56 ± 1.44 mmol L), and plasma volume change (-13.5 ± 4.4%) were greater in HIIE60 compared to all other trials ( < 0.05). One-hour post-exercise, lymphocytes decreased below pre-exercise values in all HIIE trials, and uric acid increased in the HIIE60 trial ( < 0.05). Urine lactate concentration 1 h post-exercise increased compared to pre-exercise only in HIIE60 (19-fold,  < 0.001), and this was related with the higher blood lactate concentration during exercise in that trial.

CONCLUSIONS

These findings highlight the importance of bout duration, given that shorter bouts of HIIE (30 s or 10 s) induce lower blood cell perturbations, metabolic stress, and antioxidant responses compared to the commonly used 1-min bouts, despite equal total work, duration, and work-to-recovery ratio.