EFFECTS OF PHYSICAL ACTIVITY ON AGE-RELATED DECLINE IN OXYGEN DELIVERY TO WORKING MUSCLES / 体力科学

The purpose of this study was to determine the age and habitual physical activity on re-oxygenation time in working muscles following maximal cycling exercise (CycEXmax). Twelve sedentary middle-aged (50±6), 13 sedentary elderly (66±3), 13 active middle-aged (53±5), and 20 active elderly (67±5) were evaluated the half re-oxygenation time (T1/2 reoxy) as an index of oxygen delivery, using near-infrared spectroscopy at the vastus lateralis (VL) and lateral head of the gastrocnemius (LG) after CycEXmax. T1/2 reoxys at VL and LG were significantly greater in the elderly subjects than in the middle-aged subjects in both sedentary and active groups. T1/2 reoxys at VL and LG of the active group were smaller than those of the sedentary group, regardless of age. The results of this study suggest that habitual physical activity may attenuate age-related prolongation in T1/2 reoxy in working muscles although ageing delay T1/2 reoxy in working muscles.

MUSCLE OXYGENATION HETEROGENEITY IN A SINGLE MUSCLE AT REST AND DURING BICYCLE EXERCISE / 体力科学

We evaluated regional differences of muscle O₂ dynamics between distal and proximal sites in the vastus lateralis (VL) muscle using near infrared spatial resolved spectroscopy (NIR_SRS). forty-one male subjects performed a 30 W ramp incremental bicycle exercise test until exhaustion. The NIR_SRS probes were attached on each distal and proximal site in the VL. The pulmonary O₂ uptake and heart rate were monitored continuously during the experiment. The TOI at rest was significantly higher in proximal than distal sites (65.0±5.2 vs. 69.7±4.6%, p<0.001). The TOI at exhaustion was also significantly higher in proximal than distal sites (39.5±6.7 vs. 47.5±7.6%, p<0.001). Moreover, a significant correlation was found between VO₂max and the TOI at exhaustion in each proximal and distal site in the VL. Half time reoxygenation, the time to reach a value of half-maximal recovery, was significantly slower in distal sites than proximal sites (27.1±5.6 vs. 25.0±6.1 sec, p<0.01). In conclusion, lower muscle oxygenation at exhaustion in higher VO₂max may be due to enhanced O₂ extraction in high oxidative capacity muscle. In addition, slower reoxygenation and lower muscle deoxygenation at the distal site in the VL may be explained by differences in O₂ supply and/or muscle fiber composition between distal and proximal sites.

Difference in oxygen supply-consumption balance in thigh muscles working together during knee-extension exercise / 体力科学

The purpose of this study was to clarify the changes in oxygen kinetics in two different thigh muscles recruited for dynamic knee-extension exercise at varying intensities in seven female subjects. Pulmonary oxygen uptake (Vo<SUB>2</SUB>) was measured by the 10-s mixing chamber method. Changes in oxygenated hemoglobin (HbO<SUB>2</SUB>), deoxygenated hemoglobin (Hb), and total hemoglobin (HbT) contents were measured in the vastus lateralis (VL) and rectus lemons (RF) muscles using near-infrared spectroscopy, and the oxygen saturation (SO<SUB>2</SUB>) was calculated as the HbO<SUB>2</SUB> divided by HbT in percent. The surface electromyograms (EMG) of both muscles were also recorded. The integrated EMGs (iEMG) of the VL and RF increased linearly with increasing exercise intensity up to 100%VO<SUB>2peak</SUB>. However, the HbO<SUB>2</SUB> and Hb remained unchanged when exercise intensity was below 50%Vo<SUB>2peak</SUB>, above which the increase in Hb and decrease in HbO<SUB>2</SUB> were observed. Thus the decline in SO<SUB>2</SUB> occurred at 60%Vo<SUB>2peak</SUB> in the RF, and 70%Vo<SUB>2peak</SUB> in the VL. These results suggest that muscle deoxygenation is accelerated during exercise above a certain intensity, which is lower in the RF than in the VL, during dynamic knee-extension exercise.