Reproducibility and sensitivity of muscle reoxygenation and oxygen uptake recovery kinetics following running exercise in the field

The purpose of this study was to assess the reliability of postexercise near-infrared spectroscopy (NIRS)-derived measurements and their sensitivity to different exercise intensities in the field. Seventeen athletes (24.1 +/- 5.6 year) repeated, on three occasions, two 2-min submaximal shuttle-runs at 40% and 60% of V-IFT (final speed of the 30-15 intermittent fitness test) and a 50-m shuttle-run sprint (Sprint), with (OCC) or without (CON) repeated transient arterial occlusions of the medial gastrocnemius during the postexercise period. NIRS variables (i.e. oxyhaemoglobin [HbO(2)], deoxyhaemoglobin [HHb] and their difference [Hb(diff)) were measured continuously for 3 min after each exercise. Half-recovery (1/2Rec) and mean response (MRT; monoexponential curve fitting) times of muscle reoxygenation and muscle oxygen uptake (m(V) over dotO(2)) recovery were calculated. Reliability was assessed using the typical error of measurement, expressed as a coefficient of variation (CV). Postexercise recovery of muscle reoxygenation revealed CVs ranging from 16.8% to 37.3%; CV for m(V) over dotO(2) recovery ranged from 6-2% to 20.9%, with no substantial differences shown between NIRS variables and exercise intensities. While running, intensity did not affect MRT or 1/2Rec for muscle reoxygenation, and differences were found for m(V) over dotO(2) recovery (e.g. [Hb(diff)]-m(V) over dotO(2) MRT = 28.7 +/- 5.2, 34.2 +/- 5.1 and 37.3 +/- 6.2 s for 40%, 60% and Sprint, respectively, P < 0.01). To conclude, the kinetics of postexercise NIRS measurements showed CV values ranging from 6% to 37%, with no substantial differences between exercise intensities or NIRS-derived variables. However, exercise intensity did influence m(V) over dotO(2) recovery kinetics, but not that of muscle reoxygenation in an occlusion-free condition.