Search Results

You are looking at 1 - 5 of 5 items for

  • Author or Editor: K. Shirakawa x
Clear All Modify Search
Authors: T Yano, R Afroundeh, K Shirakawa, C-S Lian, K Shibata, Z Xiao and T Yunoki

The purpose of the present study was to examine how oscillation of tissue oxygen index (TOI) in non-exercising exercise is affected during high-intensity and low-intensity exercises. Three exercises were performed with exercise intensities of 30% and 70% peak oxygen uptake (Vo2peak) for 12 min and with exercise intensity of 70% Vo2peak for 30 s. TOI in non-exercising muscle (biceps brachii) during the exercises for 12 min was determined by nearinfrared spectroscopy. TOI in the non-exercising muscle during the exercises was analyzed by fast Fourier transform (FFT) to obtain power spectra density (PSD). The frequency at which maximal PSD appeared (Fmax) during the exercise with 70% Vo2peak for 12 min (0.00477 ± 0.00172 Hz) was significantly lower than that during the exercise with 30% Vo2peak for 12 min (0.00781 ± 0.00338 Hz). There were significant differences in blood pH and blood lactate between the exercise with 70% Vo2peak and the exercise with 30% Vo2peak. It is concluded that TOI in nonexercising muscle oscillates during low-intensity exercise as well as during high-intensity exercise and that the difference in Fmax between the two exercises is associated with the difference in increase in blood lactate derived from the exercise.

Restricted access

It has been shown that the tissue oxygen index (TOI) measured by near-infrared spectroscopy oscillates at very low frequencies during recovery after exercise and that this oscillation is derived from interactions among biochemical substances involved in oxidative metabolism in skeletal muscle. As a further step, we examined whether TOI in muscle interacts through oscillation with factors related to oxygen in the cardiorespiratory system. For this examination, coherence and phase difference between the TOI in the vastus lateralis and heart rate (HR) and between TOI and arterial oxygen saturation (SpO2) were sequentially determined during recovery (2–60 min) after severe cycle exercise with a workload of 7.5% of body weight for 20 s. Significant coherence between TOI and HR was obtained in the very low-frequency band (approximate range: 0.002–0.03 Hz) and in the low-frequency band (approximate range: 0.06–0.12 Hz). The phase difference was negative in the low-frequency band and positive in the very low-frequency band. The coherence between TOI and SpO2 was significant in the very low-frequency band. The phase difference was negative. There were no sequential changes in these coherences and phase differences. The results suggest that TOI in skeletal muscle interrelates with factors related to the heart and lungs.

Restricted access
Authors: T. Yano, R. Afroundeh, R. Yamanaka, T. Arimitsu, C.S. Lian, K. Shirakawa and T. Yunoki

The purpose of the present study was to examine 1) whether O2 uptake (V̇O2) oscillates during light exercise and 2) whether the oscillation is enhanced after impulse exercise. After resting for 1 min on a bicycle seat, subjects performed 5-min pre-exercise with 25 watts work load, 10-s impulse exercise with 200 watts work load and 15-min post exercise with 25 watts work load at 80 rpm. V̇O2 during pre-exercise significantly increased during impulse exercise and suddenly decreased and re-increased until 23 s after impulse exercise. In the cross correlation between heart rate (HR) and V̇O2 after impulse exercise, V̇O2 strongly correlated to HR with a time delay of −4 s. Peak of power spectral density (PSD) in HR appeared at 0.0039 Hz and peak of PSD in V̇O2 appeared at 0.019 Hz. The peak of the cross power spectrum between V̇O2 and HR appeared at 0.0078 Hz. The results suggested that there is an oscillation in O2 uptake during light exercise that is associated with the oscillation in O2 consumption in active muscle. The oscillation is enhanced not only by change in O2 consumption but also by O2 content transported from active muscle to the lungs.

Restricted access

The purpose of this study was to determine whether tissue oxygen indices (TOIs) in two muscle groups oscillated and were synchronized in repetition of impulse exercise with high intensity. Five impulse exercises of 400 watts for 10 s were repeated with intervals of 6 min. During this period, TOI was determined by near-infrared spectroscopy in the vastus lateralis and gastrocnemius muscles. TOIs in the two muscles oscillated at rest. The TOIs rapidly decreased during each impulse exercise and then recovered and overshot after each impulse. The TOIs oscillated during each interval period. During this test period, coherent and phase differences were determined. There was high coherence between TOIs in the two muscles with a peak value at 0.019 Hz. There was a phase difference of −45 ± 32.4 degrees between TOIs in the two muscles. This phase difference corresponded to about 6 s in time scale. It seemed from this time delay that impulse exercise was not a trigger factor for the starting point of TOIs in the two muscles. It has been concluded that TOIs oscillate and are synchronized between two muscles in repetition of impulse exercise with high intensity.

Restricted access
Authors: T. Yano, C. Lian, T. Arimitsu, R. Yamanaka, R. Afroundeh, K. Shirakawa and T. Yunoki

The aim of the present study was to compare the frequency of oxygenation determined in the vastus lateralis by near-infrared spectroscopy (NIRS) in light exercise with that at rest. A subject rested in a recumbent position for 5 min and changed body position to a sitting position on a cycle ergometer for 9 min. Then exercise with low intensity (work rate of 60% of maximal oxygen uptake) was carried out for 30 min. Total hemoglobin and myoglobin (THb/Mb) suddenly decreased after the start of exercise and gradually increased for 6 min. Oxygenated hemoglobin and myoglobin (Hb/MbO2) suddenly decreased and returned to a steady-state after the start of exercise. The difference between Hb/MbO2 and THb/Mb showed a sudden decrease and then a steady-state. This difference was analyzed by fast Fourier transform. The peak frequencies of the power spectrum density (PSD) were 0.0169 ± 0.0076 Hz at rest and 0.0117 ± 0.0042 Hz in exercise. The peak frequency of PSD was significantly decreased in exercise. In exercise, the range of frequencies was expanded. It is concluded that there are oscillations at rest as well as in exercise and that the frequency of peak PSD becomes lower in exercise than at rest.

Restricted access