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The purpose of the present study was to compare oscillation of skin blood flow with that of deoxygenation in muscle during light exercise in order to determine the physiological significance of oscillations in deoxygenation. Prolonged exercise with 50% of peak oxygen uptake was performed for 60 min. Skin blood flow (SBF) was measured using a laser blood flow meter on the right vastus lateralis muscle. Deoxygenated haemoglobin/myoglobin (DHb/Mb) concentration in the left vastus lateralis were measured using a near-infrared spectroscopy system. SBF and DHb/Mb during exercise were analysed by fast Fourier transform. We classified frequency bands according to previous studies (Kvernmo et al. 1999, Kvandal et al. 2006) into phase I (0.005-0.0095 and 0.0095-0.02 Hz), phase II (0.02-0.06 Hz: phase II) and phase III (0.06-0.16 Hz). The first peak of power spectra density (PSD) in SBF appeared at 0.0078 Hz in phase I. The second peak of PSD in SBF appeared at 0.035 Hz. The third peak of PSD in SBF appeared at 0.078 Hz. The first peak of PSD in DHb/Mb appeared at 0.0039 Hz, which was out of phase I. The second peak of PSD in DHb/Mb appeared at 0.016 Hz. The third peak of PSD in DHb/Mb appeared at 0.035 Hz. The coefficient of cross correlation was very low. Cross power spectra density showed peaks of 0.0039, 0.016 and 0.035 Hz. It is concluded that a peak of 0.016 Hz in oscillations of DHb/Mb observed in muscle during exercise is associated with endothelium-dependent vasodilation (phase I) and that a peak of 0.035 Hz in DHb/Mb is associated with sympathetic nerve activity (phase II). It is also confirmed that each peak of SBF oscillations is observed in each phase.

The purpose of this study was to determine the relationship between oxygen uptake (VO2) kinetics and oxygen supply system during constant-load exercise in the supine position. The main exercises which were carried in supine position were moderate at an intensity corresponding to 80% of ventilatory threshold (VT) and heavy at an intensity corresponding to 20% of the difference between VT and peak VO2. Oxygenation level was obtained from inactive muscle by near-infrared spectroscopy (NIRS). This index is used to express the distribution of oxygen supply to inactive muscle during exercise [19]. After an exponential rise in VO2 (primary component), VO2 during moderate exercise reached a steady state, while during heavy exercise it continued to increase gradually (slow component). The HR kinetics which reflected systemic O2 supply in the supine position was similar to that of VO2 in main exercise tests. However, time constants of primary and slow components in VO2 were not significantly related to those in HR in each exercise mode. Furthermore, oxygenation level decreased after about 0.5 min from the onset of exercise and showed a minimum value at about 2 min and then recovered to the initial level during moderate and heavy exercises. Since there were no significant correlation coefficients in the time constant between VO2 and HR in each component in each exercise mode and since O2 supply to active muscle is affected by systemic O2 supply and distribution of O2 supply to inactive muscle, it is unlikely that VO2 is related to O2 supply to active muscle in supine position.