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

Area of Science:

• Exercise Physiology
• Sports Science
• Human Performance

Background:

• High-intensity interval exercise (HIIE) is a popular training method.
• The impact of varying bout durations within HIIE on physiological responses is not fully understood.
• Optimizing HIIE protocols requires knowledge of how bout length affects the body.

Purpose of the Study:

• To compare hematologic, metabolic, and antioxidant responses to HIIE with different bout durations.
• To evaluate the effects of 10-s, 30-s, and 60-s HIIE bouts against continuous exercise (CON).
• To determine if bout duration influences exercise-induced physiological perturbations.

Main Methods:

• Eleven healthy young males completed four 20-minute cycling trials: CON, HIIE10 (48x10s), HIIE30 (16x30s), and HIIE60 (8x60s).
• All HIIE trials maintained a 1:1.5 work-to-recovery ratio at 100% peak power output (PPO), with CON at 49% PPO.
• Blood and urine samples were collected pre-, immediately post-, and 1-hour post-exercise to assess hematologic, metabolic, and antioxidant markers.

Main Results:

• The 60-second HIIE bout (HIIE60) induced significantly higher post-exercise leukocyte counts, uric acid, glucose concentrations, and plasma volume changes compared to other trials.
• One hour post-exercise, lymphocytes decreased below baseline in all HIIE trials, with elevated uric acid in HIIE60.
• Urine lactate increased 19-fold post-exercise only in the HIIE60 trial, correlating with higher during-exercise blood lactate.

Conclusions:

• Bout duration in HIIE significantly influences hematologic, metabolic, and antioxidant responses.
• Shorter HIIE bouts (10-s and 30-s) elicit less physiological stress than 60-s bouts.
• Exercise protocol design, specifically bout duration, is critical for modulating exercise intensity and recovery.