Substituting Low-Intensity Endurance Exercise With High-Intensity Microintervals: Responses to Acute Exercise

Area of Science:

• Exercise Physiology
• Sports Science
• Biomedical Engineering

Background:

• High-intensity interval training (HIIT) research often focuses on sustained high intensity.
• Understanding physiological responses to oscillating workloads is crucial for optimizing training.
• Previous studies indicate VO2 and lactate can remain near the first lactate threshold (LT1) during short, intense intervals.

Purpose of the Study:

• To identify microinterval combinations that maintain physiological responses below the first lactate threshold (LT1).
• To analyze acute physiological responses, including oscillations, during microinterval training.
• To determine if microintervals can be classified as low-intensity exercise.

Main Methods:

• Thirteen endurance athletes completed four 45-minute cycling sessions.
• Continuous low-intensity exercise (CON) at 88% LT1 was compared to three microinterval protocols.
• Microintervals involved alternating 111% VO2max power with ~60W, with cycle durations of 4-6s, 7-23s, and 10-20s.

Main Results:

• Heart rate and VO2 did not exceed LT1 more during microintervals compared to CON.
• Perceived exertion was only significantly higher during the 10-20s microintervals.
• Oscillations in heart rate were significantly greater during microintervals, while VO2 oscillations were minimally increased.

Conclusions:

• Microintervals can be classified as oscillating low-intensity exercises.
• These protocols meet traditional low-intensity criteria, with minimal impact on key physiological variables.
• Microinterval training represents a novel exercise modality combining high muscular work with low metabolic disturbance.