This study focused on the effect of pressure sensation from the each plantar surface of the feet on postural control. The plantar surfaces of the feet were made less sensitive by cooling, using a specially designed apparatus set on a force plate. Three areas were cooled: the plantar surface of the heel, the forefoot, and the entire plantar surface of the foot. And the non-cooling condition was the control. The subjects, seven healthy men, were asked to track a continuously moving target spot displayed on a visual monitor while standing on the force plate. This tracking was done by controlling the center of foot pressure (CFP) by leaning forward and backward at the ankles. The target was moving at 0.025 Hertz (once per 40 seconds) with a triangular waveform. The moving range of the target was from 30 to 70 percent (%) of the total foot length from the heel, and this range was divided into 10 percent (%) subranges. Postural controllability was evaluated by the difference between movements of the CFP and target for each subrange. When the entire surface of the foot was cooled, postural controllability of moving the CFP anteriorly was significantly worse than the control. Postural controllability of moving the CFP anteriorly for the anterior and the posterior moving subranges was significantly worse than the control when the heel was cooled. When the forefoot was cooled, postural controllability of moving the CFP anteriorly for the anteriorly moving subrange was significantly worse than that of the control. These results suggest that pressure sensation from the plantar surface definitely participates in moving the CFP anteriorly for postural control. When the CFP is situated on the heel, pressure sensation from the heel alone may play a necessary role for postural control. When the CFP is situated on the forefoot, however pressure sensation from the forefoot may need to be the supplemented by sensation from the heel for adequate postural control.
The purpose of the present study is to investigate protein metabolism during rapid weight reduction. Six male boxing players put on a restricted diet of their own accord for two weeks. Body weight changes were observed and a biochemical analysis was made of their urine and blood. The initial body weight of 66.1±3.0kg (mean±SE) decreased to 63.6±3.2 kg after two weeks (P<0.01) . The changes in lean body mass (LBM) by weight reduction were not significant, but the LBM tended to decrease after two weeks. The mean caloric intake was 2, 791±728 kcal before the study and 1, 643±548 kcal after two weeks. The reduction of carbohydrate consumption is much more than that of fat and protein consumption. The 3-Me/Cr in urine increased significantly after two weeks (348.1 ± 37.0 μol/g to 508.1 f 45.6 μmol/g, P<0.01) and the increase of Urea-N/Cr in urine (8.4±0.5mg/mg creatinine to 13.7±1.3mg/mg creatinine, P<0.01) was also significant after two weeks. Urine volume decreased significantly after two weeks (P<0.01) . There was no significant difference in the blood components during the weight reduction period. These results might suggest that rapid weight reduction and massive decrease of carbohydrate intake accelerate protein catabolism.
The effects of the surface friction of a grasped object on the regulation of grip force during holding tasks using a precision grip were investigated. Using a force transducer-equipped grip apparatus, the grip force and load force acting on the object were measured continuously while surface materials (silk, wood, suede and sandpaper) and load weights (0.98N, 1.96N, 2.94N, 4.90N and 9.81N) were varied. From the recorded data, the average static grip force, slip force, safety margin force and static friction coefficient were evaluated. It was found that both the slip force and safety margin force increased as the slipperiness of the object surface increased. Significant interactions between surface type and weight were observed in the slip force and static friction coefficient. The interaction effect resulted from the fact that the frictional relationships with the fingers changed according to both weight and surface conditions. This was considered due to the viscoelastic nature of finger skin. An increase in the safety margin force with surface slipperiness was considered due to psychological reaction, probably fear of dropping the object. Unexpected changes in surface conditions caused a greater safety margin force than trials without a surface change, which might also have been associated with psychological reaction to uncertainty of the new surface condition. A relatively large inter-subject variation was found in the slip force and safety margin force relative to slippery surfaces.
We examined the time course of soleus muscle fiber type composition. Soma area and succinate dehydrogenase (SDH) activity of soleus motoneurons during three weeks of hindlimb suspension (HS) in rats. Adult female Wistar rats (n=34, 252-288g BW) were divided into four groups: control (n=8), hindlimb suspended for one week (HS 1 wk, n=8), two weeks (HS 2 wk, n=9), and three weeks (HS 3 wk, n=9) . Soleus muscle fiber composition was calculated from transverse sections stained for myosin ATPase (preincubation pH 10.3, 4.3) . The fiber type composition did not change in the HS 1 wk, but in the HS 2 wk and HS 3 wk, the proportion of type I fibers decreased and that of type IIc and ha fibers increased. Using a fluorescent neuronal tracer nuclear yellow, motoneurons innervating the soleus muscle were identified, and the soma area and SDH activity were measured. The soma area did not change for up to two weeks of HS, but decreased in the HS 3 wk. Compared with control, SDH activity of soleus motoneurons decreased in the HS 1 wk. However, in the HS 2 wk, the activity increased to the level of control. In the HS 3 wk, the activity tended to increase further. Generally, muscle fibers and their motoneurons have unitary characteristics. However, these results suggest that change in soleus muscle fiber composition are not accompanied by changes in soma area and SDH activity in soleus motoneurons during three weeks of HS.
To clarify the mechanism responsible for the increase in stroke volume (SV) due to training, we investigated the effects of interval training on the left ventricle using M-mode echocardiography. Six healthy male subjects volunteered to undergo 48 training sessions for 12 weeks (4 sessions· week-1) One session consisted of five periods of exercise of 3-min duration on a cycle ergometer at a power output of 100% maximal O2 uptake (Vo2max), interspersed with 2-min recovery cycling at 50%Vo2max. The echocardiograms at rest and during mild exercise (100W) were recorded before and after the training. The interval training significantly increased Vo2max. Although there was no significant difference in SV at rest before and after the training, the training increased SV significantly during exercise. Before the training, there was a significant difference in left ventricular enddiastolic dimension (LVEDD) and left ventricular end-diastolic volume (LVEDV) at rest and during exercise. However, after the training, LVEDD and LVEDV during exercise were significantly larger than those at rest. These results suggest that interval training for 12 weeks increases diastolic filling (elasticity) of the left ventricle during exercise in healthy young men, partly contributing to the increase in SV due to the training.