Changes in the numbers of proliferating cells and muscle fibers in growing rat skeletal muscle / 体力科学

Changes in the numbers of muscle fibers and proliferating cells detected by immunohistochemistry were studied in correlation with various growth parameters including changes in body weight, lower hindlimb length, muscle length, muscle weight and age in Wistar-strain rats at various developmental stages. The total fiber number in plantaris (PLA) muscles increased gradually between 2 weeks and 10 weeks of age (about 300g body weight), and then remained constant between 10, 000 and 11, 000 these after. In contrast, proliferating cells labeled by bromodeoxyuridine decreased gradually during the same period, and were hardly evident after 10 weeks. In the growth curves for the body weight, lower hindlimb length, muscle weight, and the length of the extensor digitorum longus (EDL) muscle, turning points were observed at 10 weeks (300 g body weight), respectively, suggesting that the turning point between growth in length and growth in width occurred at this point. Furthermore, the growth curves for the body weight and PLA muscle weight were correlated between 2 and 20 weeks, including the turning point. Therefore it is suggested that the development of muscle weight from 2 to 10 weeks depends mainly on the increment of fiber number (hyperplasia), whereas development after 10 weeks depends on the increment of individual fiber diameter (hypertrophy), in relation to the tendency for an increase in fiber number and a decrease in proliferating cells. These results indicate that maturation of skeletal muscle in male Wistar rats occurs at 10 weeks of age and a body weight of 300g. Accordingly, these facts should be considered when investigating muscle hypertrophy or hyperplasia.

Evaluation of methods used to determine anaerobic work capacity by blood lactate and oxygen debt / 体力科学

A study was conducted to examine the efficacy of indicators of anaerobic work capacity or estimations of anaerobic energy expenditure by measuring Δ blood lactate and O<SUB>2</SUB> debt after short-term maximal exercise. Eight male subjects performed cycle ergometer pedaling against 5.5-7.0 kp resistance with maximal effort for 45 s. After pedaling, venous blood samples were drawn serially at 1 min intervals from 1 to 10 min, for measurement of peak blood lactate. Anaerobic energy expenditure was determined in terms of both alactacid and lactacid energy expenditure, on the basis of Δ blood lactate (L-method) and O2 uptake kinetics (D-method) during recovery.<BR>The following results were obtained:<BR>1) The correlation coefficient between lactate and performance was higher (about 0.3-0.5) when lactate was expressed as the estimated value of lactate production rather than Δ blood lactate. A significant relationship (r=0.740, p<0.05) was found between lactate production and peak power.<BR>2) When O<SUB>2</SUB> uptake after recovery for 60 min did not recover to the baseline of O<SUB>2</SUB> uptake at rest, O<SUB>2</SUB> debt was calculated using a baseline of O<SUB>2</SUB> uptake just before the end of recovery. This O<SUB>2</SUB> debt was significantly correlated with work at any time of recovery.<BR>3) There was a significant relationship between lactate production and lactic O<SUB>2</SUB> debt, which was significantly correlated with work.<BR>4) When lactacid energy was calculated using a formula of 1.7×Δ blood lactate and 0.3 kcal/g lactate, there was no significant difference between anaerobic energy expenditure calculated by the L- and D-methods for up to 30 min during recovery.<BR>It was concluded that a) the estimated value of lactate production and O<SUB>2</SUB> debt calculated using a baseline of O<SUB>2</SUB> uptake just before the end of recovery could be employed as an indicator of anaerobic work capacity, and b) Δ La multiplied by a coefficient of 1.7 and 0.3 kcal/g lactate was more appropriate for estimating anaerobic expenditure in short-term maximal cycle ergometer pedaling.

The influence of leg length discrepancy on the pelvic obliquity, scoliosis, leg strength, and leg injury in track and field athletes / 体力科学

Fifty-two trained athletes (15 short-distance runners, 20 long-distance runners, and 17 jumpers) and 5 controls were examined for leg length discrepancy, pelvic obliquity, scoliosis, leg strength discrepancy, and leg injury. Forty-seven subjects (90%) in the trained group and 4 subjects (80%) in the control group had leg length discrepancies. Differences of the femur lengths and tibia lengths, not of the joint space or soft tissue, were main factors of leg length discrepancies. There were no significant differences in leg length discrepancy and in pelvic obliquity between the trained and control groups. The trained group had twice as many leg length discrepancies and pelvic obliquities as the control group in average. A positive correlation between leg length discrepancy and pelvic obliquity was noted (p<0.001) . Among the jumpers, those who had suffered from hamstring muscle strain showed significantly more discrepancies in the right and left knee flexion strengths than the jumpers who had never experienced such muscle strain (p<0.41) . The rate of knee flexion strength against extension strength was significantly lower in the jumpers who had experienced knee joint injuries (p<0.01) .<BR>The results indicate that leg length discrepancy affects on the pelvic obliquity and scoliosis. Differences of the femur lengths and tibia lengths were main factors of length discrepancy. It is possible that an inequality of load on the right and left legs may cause leg length discrepancy.