ABSTRACT
To examine the relationship between sports activity and bone mass acquisition, we observed one-year changes in the bone mineral content and density (BMC and BMD) of weight-bearing and non-weight-bearing bone in 68 college women who had participated in various sports since the age of 18.5 years on average. Based on their sports experience, the subjects were divided into four groups: Group A: 18 students who have not had participated in any kind of sports activity since junior high school days ; Group B: 8 students who had participated in team sports at junior and senior high school, then stopped practicing after entering college ; Group C: 14 students who had participated in team sports since junior high school ; Group D: 28 rhythmic sports gymnasts. Whole-body and regional BMC in the head, trunk, arms and legs, and BMD of the lumbar spine and proximal femur were measured using an XR-26 DXA scanner. Height, weight and calcium intake were similar among the four groups, and during the experiment their values changed little. With regard to annual changes in BMC and BMD for weight-bearing regions: 1) In Group A, no signifi-cant increases were observed in any of the body regions; 2) In Groups B and C, only the lumbar spine showed a significant increase. Comparing the changes in BMD in these two groups, Group C showed a larger increase than Group B, although the value did not reach statistical significance ; 3) In Group D, significant increases in BMD for the lumbar spine and femoral neck and in BMC for the trunk and legs were found. The annual changes in BMD were significantly higher than Group A. As to annual changes in non-weight-bearing bones such as those in the head and arms, there were not significant differences among the groups. These data indicate that sports practice may affect changes in bone mass in weight-bearing regions in female college students. Furthermore, it is possible that the amount and quality of sports training may influence the peak bone mass and its timing.
ABSTRACT
In recent years, the knee extensor forces of athletes have usually been evaluated by measuring isokinetic output torque. The purpose of this study was to confirm the usefulness of normalizing the torque (force) -velocity curve and calculating the maximal power of knee extensor under isokinetic contraction.<BR>Seventy two (46 elite, 26 non-elite) Japanese male sprinters were chosen as the subjects in this study. The peak torque of the dominant side of knee extensor was measured by using the isokinetic dynamometer (Cybex II<SUP>+</SUP>) in three different angular velocities of 60, 180, 300 deg/sec. Moreover, the isometric torque (0 deg/sec) was measured in 39 athletes, 120 and 240 deg/sec of contraction were performed in 12 out of 39 athletes.<BR>The exponent equation (<I>F = F<SUB>o</SUB>× e<SUP>av</SUP>- kv</I> : Fenn 1935) was applied to normalize the torquevelocity curve without including the coefficient of viscosity (<I>k</I>) . The maximal power and its optimal velocity was presumed from this torque-velocity curve. The average of measured torque at 0 deg/sec contraction (<I>F<SUB>0</SUB></I>) was lower than that of 60 deg/sec, therefore<I>F<SUB>0</SUB></I>was presumed as the same as the maximal power. Those parameters were not significantly different when calculated from 3 velocities (60, 180, 300 deg/sec) and 5 velocities (plus 120, 240 deg/sec) in 12 athletes. For this reason, each parameter was calculated from 3 velocities.<BR>The maximal torque (<I>F<SUB>0</SUB></I>/BW) was the same between elite and non-elite group (4.0 Nm/kg) . Nevertheless, the coefficient of torque loss (<I>a</I>), maximal power and its optimal velocity were significantly different (-0.1586 : -0.1908, 9.6 : 7.8 watt/kg, 373: 309 deg/sec, respectively. P<0.01 Student-t) . It was said that to normalize the torque-velocity curve or to presume the maximal knee extension power and its optimal velocity were useful to assess the muscle function or the performance of athletes under isokinetic contraction.