The recent development of microneurographic techniques for obtaining direct intraneural recordings of human muscle sympathetic nerve activity (MSNA) has revealed much new information about sympathetic control mechanisms during exercise over the last decade. From numerous investigations, the major findings are how the pattern and magnitude of the MSNA response to exercise is influenced by many factors such as exercise type (static and dynamic exercise, active muscle mass and combination exercise), intensity, duration, muscle fiber type, fatigue and exercise training. Furthermore, environmental conditions, i.e., postural change, hypoxia, thermal and cold stress, genders and age are also factors modulating the MSNA response during exercise. The most important mechanism of stimulating MSNA during exercise is metaboreflex from the active muscles, while the reflex can be modulated by central and peripheral factors. Especially, afferent neural input from the mechanoreceptors in the skeletal muscle, arterial and cardiopulmonary baroreceptors, and peripheral chemoreceptors could play an important role in precise control of MSNA during different exercise situations. On the basis of the current state of information, accumulated knowledge of this area of research may be critical for understanding the contribution of MSNA for control of exercise circulation as well as counteracting muscle fatigue or improvement of exercise performance.
A study was performed to compare joint torque development with EMG activities, and to investigate the relationship between peak torque and power during different phases of leg movement at different sprint velocities from the starting dash to full stride. Cinematographic recordings of sprint movement together with ground reaction forces and EMGs from seven lower limb muscles were obtained from four male sprinters at the 1st, 3rd, 5th, 9th, 13th and 19th (maximal velocity) steps from the sprint start. Joint torque and power in the hip, knee and ankle were computed from analysis of the film and ground reaction forces. The results can be summarized as follows: 1) The developmental patterns of joint torque and power, and the EMG activities were similar from the first step to the maximal velocity. 2) The phases of torque development were parallel to the related EMG activities. 3) Stretch-shortening cycles of muscle were observed in the m. Soleus during the foot contact period and in the m. Biceps femoris during the latter half of the swing period. 4) There was no peak torque or power that showed a decrease with increased sprint velocity. 5) Peak torque and power that increased with sprint velocity were (a) torque and positive power of the hip flexors during the first half of the swing period, (b) torque of the hip extensors during the latter half of the swing period, (c) torque and negative power of the knee extensors during the first half and latter half of the swing period, (d) torque of the ankle extensors during the middle of the foot contact period, (e) negative power of the ankle extensors during the first half of the foot contact period, and (f) positive power during the latter half of the foot contact period. These results suggest that muscles in the hip and knee joints cooperate with the change in swing movement, and that muscles in the ankle joint cooperate with the change in drive movement as sprint velocity increases. 6) The peak torque and power that remained high independent of sprint velocity were (a) torque and positive power of the hip extensors from the middle of the swing period to the middle of the foot contact period, (b) torque of the ankle extensors during the foot contact period, and (c) power of the ankle extensors during the latter half of the foot contact period. These results indicate the importance of the hip extensors and ankle extensors in sprinting.
The purpose of this study were to investigate factorial structures of physique and physical fitness, and to determine the change of physique and physical fitness with age and its sex difference in the elderly. Nineteen test items were selected from 5 domains of physique, muscle function, joint function (flexibility), neuromuscular function and lung function, considering the validity, safety and convenience of tests. The subjects were 207 males and 226 females aged 65 to 89 years. Factor analysis was applied to each correlation matrixes consisting of 8 physique variables and 11 physical fitness variables. In physique domain, three extracted factors were interpreted as body fat, body linearity and body bulk. Body bulk and body linearity in both sexes and body fat in females decrease significantly with age. Body linearity was found significantly larger in males than females. Body fat was significantly greater in females. In physical fitness domain, four factors were extracted and interpreted as muscular strength, balance, agility of upper and lower limbs, and flexibility. A significant declining trend with age was found in the above-mentioned physical fitness elements both sexes. Also, significant sex differences in muscular strength, balance, and flexibility were found, and males were superior to females except for flexibility. It was inferred that the influence of aging in muscular strength and balance is greater flexibility and agility of upper and lower limbs in the elderly. Further, the decrease of muscular strength seems to facilitate the decline of balance with age.