The effect of endurance training on resting oxygen stores in muscle evaluated by near infrared continuous wave spectroscopy.

The purpose of this study was to examine the effects of endurance training (ET) on resting oxygen store (r-O(2)mus) using near infrared continuous wave spectroscopy (NIR(CWS)), and the validity of using this method for the evaluation of resting muscle oxygen consumption (r-VO(2)mus) in a training study. Ten female subjects were tested in the following study. All subjects were physically active, but did not participate in any regular training besides this study. The subjects were fully informed of the risks and gave their consent before the start of the experiments. For ET subjects cycled for 40 min at 60-70% VO(2)peak, three times a week, for 4 weeks. Before and after the period of ET, VO(2)peak and r-O(2)mus for the vastus lateralis muscle were measured. r-O(2)mus was defined as the amount of O(2) consumed by the muscle, which was determined from r-VO(2)mus measured by NIR(CWS) (HEO200, Omron) during arterial occlusion induced by a pneumatic tourniquet. In order to verify the measurements using NIR(CWS), oxygen consumption for both the whole body (40%-VO(2)) and vastus lateralis muscle (40%-VO(2)mus) were measured at pre and post ET. 40%-VO(2)mus was calculated from the ratio of the declining rates of Hb/MbO(2) immediately post-exercise and during rest (r-VO(2)mus). As a result, VO(2)peak significantly increased after ET. r-O(2)mus also significantly increased (p < 0.05). Neither 40%-VO(2) nor 40%-VO(2)mus changed following ET. Therefore these findings suggest the increase in r-O(2)mus calculated from r-VO(2)mus reflects an increase in resting oxygen stores in the trained muscle. Under the condition when resting muscle oxygen consumption is unchanged, NIR(CWS) can be a useful non-invasive tool for measuring muscle oxygen stores.