Influence of isometric RPE-clamp exercise on fatigability, muscle oxygenation dynamics, and microvascular function in healthy young adults

Purpose

This study investigated fatigability, reflected by torque responses and time to task failure (TTF), and time course of muscle oxygenation (SmO₂) dynamics, as well as microvascular function assessed by near-infrared spectroscopy-vascular occlusion test (NIRS-VOT), in response to low-intensity, isometric forearm flexion anchored to a constant rating of perceived exertion (RPE) level of 3 (0–10 scale).

Methods

Twenty-five healthy young adults (22.9 ± 4.8 yr) completed a pre-exercise VOT, maximal voluntary isometric contraction (MVIC), and RPE-clamp exercise (RPE = 3), followed by post-exercise MVIC and VOT. Initial torque, TTF, and SmO₂ dynamics were recorded during the RPE-clamp exercise. The time course of SmO₂ was analyzed in 5 % TTF segments. During the VOTs, slope 1 (desaturation rate), minimum SmO₂, slope 2 (reperfusion rate), maximum SmO₂, and area under the curve (AUC) were recorded.

Results

MVIC torque significantly decreased from pre- to post-exercise (−13.9 % ± 14.0 %; p < 0.001). Initial torque was 23.3 ± 10.3 % MVIC, and TTF was 436.3 ± 252.0 s. SmO₂ declined significantly from 0 % to 5 % TTF (p = 0.005), but returned to the initial value and remained stable across subsequent time intervals. Compared to pre-VOT, post-VOT exhibited significantly lower slope 1 (p < 0.001) and minimum SmO₂ (p = 0.002), and greater maximum SmO₂ (p = 0.013), while slope 2 (p = 0.065) and AUC (p = 0.379) were unchanged.

Conclusions

During the RPE-clamp exercise, the voluntary reduction in torque to maintain the assigned RPE likely resulted in stable muscle oxygen availability, preventing the development of hypoxic stimulus needed to enhance microvascular responsiveness. However, the low-intensity isometric RPE-clamp exercise combined with a post-VOT may enhance muscle aerobic metabolism through sustained oxygen utilization.