Comparison of oxygenation kinetics measured by different placements of the NIRS probe during sustained isometric gripping

The purpose of this study was to compare oxygenation kinetics measured by slightly different placements of a near-infrared spectroscopy (NIRS) probe during sustained isometric gripping. Oxygenation kinetics of sixteen young adult males was measured with two NIRS probes attached to the flexor carpiradialis muscle during gripping for 3 min. One probe (channel 1) was attached at one-third the length of a line from the medial epicondyle of the humerus to the styloid process of radius. Another probe (channel 2) was attached at the palmaris longus. Although the cross-correlation coefficients for the two probe placements regarding oxygenated hemoglobin (oxy-Hb/Mb), deoxygenated hemoglobin (deoxy-Hb/Mb) and tissue oxygenation saturation (StO₂) were low (r_xy, 0.119–0.405), Pearson’s correlation coefficients for the times to reach almost steady state for these parameters were very high (oxy-Hb/Mb, r=0.878; deoxy-Hb/Mb, r=0.769; StO₂, r=0.843; p<0.05). The difference of oxygenation kinetics between the probe placements may reflect the difference of fiber recruitment characteristics in the flexion muscle group. In conclusion, to obtain a stable measurement, it is important that the NIRS probe is placed at the same anatomical point.