In this study, we investigated the effect of acute exercise on the mitochondrial structure of hepatocytes surrounding the terminal hepatic venule (zone III) in the rat liver acinus. Male SD rats were assigned to a resting group (n=8) and to running groups ran on a motor-driven treadmill for 100 min (n = 8) or did continued running beyond 100 min until exhaustion (n = 5) . Plasma guanase activity was increased with duration time of exercise. The arterial ketone body rate (AKBR) increased during the 100 min of running, but the AKBR significantly diminished with exhaustive running as compared with that for 100 min of running. Although there was no change in the mitochondrial structure of hepatocytes in the perportal area (zone I) during exhaustion, remarkable swelling was observed in that in zone III. These results suggest that acute running affects mitochondrial structures in zone III, and that this might be a hypoxia zone during exercise.
Twenty-four male university baseball players were each requested to throw a baseball, and filmed using the direct linear transformation method of three-dimensional (3D) videography. 3 D coordinates of landmarks were obtained. Resultant joint forces and resultant joint torques in the wrists, elbows, shoulders, neck, and upper torso joints were calculated using the inverse dynamics method. The mechanical powers caused by the resultant joint forces (joint force power) and by the resultant joint torques (joint torque power) of each segment were calculated, and the mechanical work was also obtained by integrating the joint torque powers with time. Peak values of energies of the upper torso, upper arm, forearm, hand, and ball appeared in sequence from the proximal segment to the distal segment. The joint force powers in any segment were markedly larger than the joint torque powers. Little joint torque power was produced in the wrist throughout the throwing motion. The negative joint force power and joint torque power at the proximal end of the upper torso were rapidly increased immediately after the foot contact stride. It was clarified that the appearance of the large energies in the distal throwing arm segments during the final phase of throwing motion were caused mainly by transfer of the energies produced by the motions of the torso and shoulder joints. This paper discusses the mechanical energy flows of the upper torso and upper limb segments during the motion of baseball throwing.
The purpose of this study was to investigate the relationships between muscle mass or muscle power and bone mineral density in 43 postmenopausal women. Single photon absorptiometry was used to measure the bone mineral density and bone width of the calcaneuse. Isotonic muscle power of knee extensions (KE), knee flexions and incline squats (ISQ) were measured, using the power processor (VINE Co., Ltd.) . Statistical analysis demonstrated a significant positive correlation (p<0.05) between bone mineral density and lean body mass or muscle thickness. Although, bone mineral density was not significantly correlated with body mass index or fat mass, it was significantly corre-lated with leg muscle power. Further, the bone mineral density was also positively correlated with muscle contraction speed in the motion of KE (p<0.01) and ISQ (p<0.05), but not with muscle strength. This data suggest that the bone mineral density is closely related to the muscle power and/or speed rather than the muscle strength in postmenopausal women.
The use of mouth guards in contact sports effectively prevents oral injuries and preserves oral structures. Many contact sports in which a high impact collision could easily cause oral injury do not require athletes to use mouth guards. We discuss the circumstance of oral injury and awareness concerning the use of mouth guards in Japanese high school soccer and rugby and basketball teams. During an interview, each athlete was asked a series of questions concerning their history of oral injury while participating in sports and actual circumstances of using a mouth guard. The incidence of oral injuries was 32.3% in soccer, and 56.5% in rugby, 46.6% in basketball while 0.8% of athletes possessed some type of mouth guard in soccer, 24.1% in rugby and 1.3% in basketball. Although 81.8% of soccer athletes and 81.2% of basketball athletes thought mouth guards were unnecessary, only 26.2% of rugby athletes shared this opinion. Many athletes playing soccer and basketball had insufficient knowledge about mouth guards, and were not interested in preventing oral injury. Due to the diversity of sports that can produce oral injury, it is recommended that mouth guards be worn by all individuals participating in rugby, soccer and basketball.
The response of systolic blood pressure (SBP) to pedalling exercise was studied in 32 healthy young men. The subjects performed the exercise at different intensities for 3 min using an incremental loading method. The first work load was 30W and increased by 30W until the heart rate (HR) reached about 170 bpm. SBP at HR 100. 160 bpm (SBP@HR 100-160) was calculated from the cubic regression equation in each subject. Mean SBP and SEM at HR 100, 110, 120, 130, 140, 150, 160 were 143.9 (2.49), 152.9 (2.79), 161.6 (3.02), 170.0 (3.16), 177.8 (3.25), 184.5 (3.34), and 189.7 (3.45) mmHg, respectively. However, the rate of elevation of SBP was zero at HR 175 bpm, which was calculated from the cubic regression equation. This may indicate that SBP is inhibited by baroreceptors and other factors at HR above 170 bpm. There were no significant relationships between SBPs@HR 100-160 and indices of aerobic capacity such as maximal oxygen consumption or PWC 170. Double product (DP) as an index of oxygen consumption by cardiac muscle increased with HR without any reduction in its rate of elevation during exercise.
The purpose of this study was to assess an alteration of cardiac autonomic nerve activity during water immersion. Ten healthy young males (age : 21-28 yr.) were immersed in water at the temperatures of 25°C, 30°C and 34°C. Subjects sat calmly for 20 minutes in sitting position before water immersion, and then were immersed in water at subaxillary level in sitting position for 15 minutes, performing controlled breathing (15 cycle/min.) . Electrocardiograms were recorded continuously. Autonomic nerve activity was estimated with the analysis of power spectral by using the Fast Fourier Transformation (FFT) . High (HF ; 0.15-0.50 Hz) and low (LF ; 0.04-0.15 Hz) frequency areas and the ratio of LF to HF (LF/HF) were calculated as the indices of cardiac parasympathetic nerve activity, sympathetic nerve activity with parasympathetic modulation, and sympathetic nerve activity, respectively. During the water immersion at 25°C, 30°C and 34°C, HF was significantly increased, while the heart rate and LF/HF were significantly decreased. There were no statistically significant differences among both of HF and LF/HF during the immersion at 25°C, 30°C and 34°C, although the rate of change in HF at the temperature of 25°C appeared to be prominent compared to those at 30°C and 34°C and some subjects showed an exaggerated change in HF immediately after immersion. These results suggest that cardiac parasympathetic nerve activity is enhanced and cardiac sympathetic nerve activity is suppressed during a short time water immersion at the thermo-neutral temperature (34°C) and the temperatures of 25°C and 30°C, which are the usual temperatures found in indoor pools.
Aerobic dance (AD) is a form of fitness exercise whose program is constructed by a combination of various joint movements. Therefore the exercise is expected to give enough stimulus to not only the cardiorespiratory but also the musculoskeletal system. The purpose of this study was to evaluate the activity level of the leg muscles among the major 22 AD leg movements, or steps (13 low-impact steps and high-impact steps), by electromyography (EMG) analysis. The subjects were two trained AD instructors, who were asked to perform individual steps at a pitch of 144 bpm. EMG data were recorded from the iliopsoas, gluteus maximus, vastus lateralis, biceps femoris, tibialis anterior, and gastrocnemius muscles on the right side by means of surface electrodes. The half-wave of the raw EMG was rectified and integrated over periods of 20 s during the exercise. From the raw EMG data it was observed that the pattern and amplitude of the electrical discharge of each muscle varied in response to the difference in step motion. The integrated EMGs of the iliopsoas, biceps femoris, and gastrocnemius tented to show higher values for high-impact steps in comparison with low-impact steps, but that of the tibialis anterior showed a contrary trend. The mean value and stan-dard deviation of iEMG of each muscle for the 22 steps was calculated for the same subjects, and the muscle activity level was classified into 5 degrees. Making use of this evaluation table, it may be possible to construct an AD program that can activate the leg muscles impartially.