Acute knee extensor torque and muscle oxygenation responses to isometric testing in exercise and non‐exercised legs of male adults

Abstract Portable near‐infrared spectroscopy (NIRS) provides a noninvasive measure of local muscle metabolic demand through muscle oxygen saturation (SmO 2 ). This study aimed to evaluate acute SmO 2 responses in exercising and non‐exercising muscles during an isometric test conducted before and after exercise. Twelve physically active men (25 ± 6 years; 1.75 ± 0.07 m) performed three maximal voluntary contractions (MVC) and a 45‐s isometric contraction at 70% MVC (IC70%) before and after completing five sets of 30 concentric knee extensions at 180°·s −1 , with 60 s rest between sets, on an isokinetic dynamometer. SmO 2 was recorded in the vastus lateralis (exercised and non‐exercised leg) and triceps brachii. Significant differences in SmO 2 were observed between exercised and non‐exercised legs both pre‐ ( p = 0.048) and post‐exercise ( p < 0.001), whereas no significant changes were found in the triceps brachii or non‐exercising vastus lateralis. Acute responses to isometric exercise differed between SmO 2 and torque measures. While the torque of the IC70% did not change following the exercise protocol, SmO 2 showed a higher deoxygenation response during exercise. The isometric test did not indicate any redistribution of muscle oxygenation from non‐exercising to exercising muscles. These results provide novel insights into the dissociation between mechanical and microvascular responses during isometric exercise and support the potential of this test as a practical tool for monitoring training loads.