Establishing VO2peak-based exercise intensity classification and physiological validation in ICR mice.

Abstract

Purpose: This study aimed to develop a VO2peak-based framework for classifying exercise intensity in ICR mice and to validate the associated physiological responses.

Methods: Male ICR mice (8 weeks) completed four maximal graded exercise test (GXT) protocols (P1-P4) using a treadmill-equipped metabolic chamber. P1 and P2 began at 10 m/min with a fixed 15° incline, increasing speed by 3 m/min every 3 min (P1) or 1.5 m/min every 1.5 min (P2). P3 and P4 also started at 10 m/min but from a 0° incline; P3 increased both speed (3 m/min every 3 min) and incline (3° every 3 min), while P4 increased speed (1.5 m/min every 1.5 min) and incline (1.5° every 1.5 min) until 15°, after which only speed increments continued. VO2peak values were then used to calculate running speeds at 40%, 60%, and 80% VO2reserve to represent low, moderate, and high intensity, respectively. Constant-load tests (CXT) at these speeds measured metabolic responses and blood lactate concentrations.

Results: VO2peak did not differ significantly among protocols, but P4 showed greater variability. Target speeds were therefore determined from P1-P3. During CXT, oxygen consumption, energy expenditure, and VO2plateau rose with intensity, and blood lactate at 60% and 80% VO2reserve exceeded that at 40%, with 60% surpassing the 4 mM aerobic-anaerobic threshold.

Conclusion: These findings provide standardized VO2peak-based reference values for classifying exercise intensity in ICR mice. Fixed-incline GXT protocols reduce variability, and the derived speed thresholds can guide future exercise interventions.