Investigation of muscle oxygen saturation response according to quadriceps muscle strength levels
The assessment of muscle oxygenation during isokinetic testing has gained increasing interest by use of near-infrared spectroscopy (NIRS). However, it remains unclear whether muscle oxygenation responses differ according to muscle strength level. This study aimed to investigate changes in quadriceps muscle oxygen saturation (SmO 2 ) and total haemoglobin (tHb) during isokinetic maximal testing at different angular velocities. Forty-six participants were divided into moderate (n = 23) and high strength groups (n = 23) based on normalized peak moment of the knee extensors at 60°/s. SmO 2 and tHb were measured using NIRS at rest, during isokinetic testing at 60°/s and 180°/s, and during recovery on dominant leg. A mixed-design ANOVA was used to examine group, time, and interaction effects. Significant main effects of time were found for SmO 2 (p < 0.001) and tHb (p = 0.012), indicating dynamic changes across the protocol. However, no significant group or group × time interaction effects were observed (p > 0.05). Correlation analyses showed moderate associations between tHb and isokinetic strength parameters at 180°/s; however, these were based on pooled data. Isokinetic testing at different velocities resulted in significant changes in SmO 2 and tHb, whereas muscle strength level did not significantly influence these responses.