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.
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.
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 μm² to 13, 000 μm², 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/mm², 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 VOG₂max was 68.5 ml/ kg/min (4, 066 ml/min), while VO₂@AT averaged 45.9 ml/kg/min (2, 756 ml/min) . And it was found that VO₂max and VO₂@AT correlated significantly with % ST, CC (/ST) and SDH activity. Particular, VO₂ max was most strongly related to SDH activity (r=0.612, p<0.01) .
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.