This cross-sectional observational study examined muscle oxygen saturation (SmO₂) and additional Near-Infrared Spectroscopy (NIRS)-derived parameters—oxygenated hemoglobin (O₂Hb), deoxygenated hemoglobin (HHb), hemoglobin difference (Hb Diff), and total hemoglobin levels (tHb)—in the vastus lateralis (VL) and biceps femoris (BF) muscles between athletes and sedentary individuals during isokinetic maximal concentric (CON) and eccentric (ECC) contractions executed at 60, 180, and 300°/s speeds. Thirty-one male participants (17 elite volleyball athletes, 14 sedentary) underwent a testing protocol using an isokinetic dynamometer. NIRS sensors recorded SmO₂, O₂Hb, HHb, Hb Diff, and tHb on the VL and BF during maximal CON and ECC sets at each speed. Two-way repeated-measures ANOVA (speed × group × contraction) was applied; normality was verified (Shapiro–Wilk), and Greenhouse–Geisser corrections were used if needed. Data are reported as mean ± SD. In the VL, high speed (300°/s) significantly raised SmO₂ and tHb relative to 60°/s (p < 0.05). In BF, SmO₂ was stable across speeds, although Hb Diff increased at 300°/s (p = 0.008). At 60°/s, VL CON produced greater tHb, O₂Hb, and Hb Diff than ECC (p < 0.001); in BF at 60°/s, ECC produced higher O₂Hb and Hb Diff than CON (p < 0.001). Athletes had higher VL tHb and O₂Hb than sedentary individuals (p < 0.05); BF group differences were minimal. Isokinetic velocity and contraction mode significantly altered muscle oxygenation in a muscle-specific manner. High-speed isokinetic CON exercises may enhance oxygenation and local blood flow in the VL of the quadriceps, potentially supporting muscle function, while the hamstrings’ limited responsiveness to speed variations highlights the need for alternative strategies. CON vs. ECC actions also elicited distinct oxygenation in each muscle, reflecting differences in contraction-specific physiological demands. These findings – based on measured NIRS variables – highlight how velocity, contraction type, and training status modulate muscle oxygen dynamics, providing a physiological basis for tailoring training and rehabilitation protocols.
Samand et al. (Mon,) studied this question.