Changes in systolic and diastolic time intervals during prolonged exercise. (Part 2) / 体力科学

A study was undertaken to determine whether the specific change in the ratio of systolic to diastolic time (QS<SUB>2</SUB>/DT) observed during prolonged exercise<SUP>17)</SUP> is dependent on HR or elapsed time, and also to elucidate the possible relationship between change in QS<SUB>2</SUB>/DT and distance-running performance. Twelve male distance runners were divided into two groups, a high- (HP Group) and a low-performance (LP Group) group, according to their 10, 000-meter running performance. They performed 60-min exercise on a bicycle ergometer at a work load controlled so as to keep the HR at 150 bpm. HR, systolic time intervals (STIs) and DT were calculated from electrocardiogram, phonocardiogram and the derivative of ear densitogram.<BR>In the time course of QS<SUB>2</SUB>/DT, two crests were formed at 2 and 15 min after the start of exercise, and also two troughs were formed at 10 and 20 min. Some of these troughs and crests formed even when HR was kept constant. Patterns of change in QS<SUB>2</SUB>, DT, QS<SUB>2</SUB>/DT and other parameters were similar in the two groups. However, the absolute values of the parameters differed. QS<SUB>2</SUB>, left ventricular ejection time (LVET) and QS<SUB>2</SUB>/DT in the HP Group were lower than those in the LP Group, whereas DT in the HP Group was longer than that in the LP Group.<BR>From these findings, it was concluded that the specific change seen in QS<SUB>2</SUB>/DT during prolonged exercise is dependent not on the HR level but on elapsed time. The changes in STIs and DT during prolonged exercise are thus influenced by the distance-running performance of the subjects.

Systolic and diastolic time intervals during prolonged exercise of a constant intensity / 体力科学

The purpose of this study was to elucidate the changes in systolic and diastolic time intervals which accrue along with increase of HR during a prolonged exercise.<BR>Fifteen male collegiate distance runners performed bicycle ergometer exercise of 70% maximal oxygen intake for 60 minutes. Electrocardiogram, phonocardiogram, pulse wave using ear densitogram and its derivative were recorded throughout the exercise, and then HR, STI, DT (diastolic time) and QS<SUB>2</SUB>/DT were caluculated from the tracings.<BR>The results obtained are as follows:<BR>1. At the initial phase of the exercise, DT decreased markedly to result in rapid increase of QS<SUB>2</SUB>/DT. When HR was between 130-150 beats/min, however, the rate of decrease of QS<SUB>2</SUB> was greater than that of DT, so QS<SUB>2</SUB>/DT showed a tendency to decrease. When HR was more than 150, QS<SUB>2</SUB> reached a plateau but DT still continued to decrease, and QS<SUB>2</SUB>/DT turned to increase again.<BR>2. LVET decreased slowly throughout the exercise, whereas PEP decreased rapidly within initial two minutes and kept a steady state thereafter. The change in QS<SUB>2</SUB> after two minutes of exercise seemed to depend on LVET.<BR>3. LVETi and QS<SUB>2</SUB>i showed a similar change as that in QS<SUB>2</SUB>/DT but the change in QS<SUB>2</SUB>i was less obvious than that in LVETi.<BR>4. PEN and PEP/LVET decreased rapidly in the initial two minutes, thereafter they continued to increase more slowly with increase of HR until the end of exercise.<BR>Conclusively, HR continued to increase monotonously during prolonged exercise of a constant intensity, while systolic and diastolic time intervals varied the directions and patterns of their changes during the exercise.

Relationship between muscle fiber composition, capillary supply, oxidative enzyme activity and aerobic work capacity in middle- and long-distance runners / 体力科学

It was the purpose of this study to examine the property of skeletal muscle fiber in middle- and long-distance runners, and to evaluate the relationship between the property of skeletal muscle fiber and aerobic work capacity.<BR>Biopsy samples were taken from M, vastus lateralis of 23 middle- and long-distance runners, and analyzed for muscle fiber composition, capillary supply and SDH activity. Aerobic work capacity was measured on a treadmill with continuous method.<BR>The mean value for % ST in M. vastus lateralis was 61.3%, and the muscle fiber distribution showed the tendency of slow type. The crosssectional area of ST and FT fibers ranged approximately from 3, 000 μm<SUP>2</SUP> to 13, 000 μm<SUP>2</SUP>, and the cross-sectional area of ST fiber tended to be larger than that of FT fiber. The mean values for CD, C/F ratio, and CC (/ST) as capillary supply were 279/mm<SUP>2</SUP>, 1.62 and 5.7, respectively. The mean value for SDH activity was 5.86 μmoles/g/min, and was lower than reported previously for elite runners. In addition, SDH activity correlated with % ST and CC (/ST) (r=0.480, p<0.05, r=0.640, p<0.01) . On the other hand, the mean value for VOG<SUB>2</SUB>max was 68.5 ml/ kg/min (4, 066 ml/min), while VO<SUB>2</SUB>@AT averaged 45.9 ml/kg/min (2, 756 ml/min) . And it was found that VO<SUB>2</SUB>max and VO<SUB>2</SUB>@AT correlated significantly with % ST, CC (/ST) and SDH activity. Particular, VO<SUB>2</SUB> max was most strongly related to SDH activity (r=0.612, p<0.01) .<BR>The results of this study suggest that in regard to middle- and long-distance runners, structural characteristics of the ST fiber and capillary are some of the indispensable factors to regulate such a functional property as SDH activity and that the distinctive characteristics of the skeletal muscle fiber might possibly influence aerobic work capacity to a great extent.