In this study, the electrical activity patterns of the antagonistic bi-articular and mono-articular muscles of upper extremity, during in the hand contact period of in front handsprings in tumbling, were analyzed in terms of electromyographic (EMG) kinesiology and robotics. The mechanical two-joint link models equipped with a pair of the antagonistic bi-articular muscles in addition to two pairs of the antagonistic mono-articular muscles were used for robotics analyses. Reversal of triceps brachii long head (Tlo) and biceps brachii long head (Blo) activities was responsible for changes in the output force direction during the hand contact period. It was confirmed that the coordinating activity pattern of three pairs of the antagonistic muscles contributed to the output force control and the output force direction control. The results obtained here suggest the importance and necessity for coordinated muscle activities of bi-articular and mono-articular antagonistic muscles for analyses of sports.

The purpose of this study was to clarify the characteristics of the walking movements for the elderly compared with young adults. The walking analysis compared were 1) free walking; 2) walking within similar range of speeds; and, 3) walking of overall range of speeds during slow to fast walking. Ten healthy young men (21 to 24 years of age) and ten healthy elderly men (66 to 73 years of age) participated as the subjects in this study. The angle data of the right knee joint and that of the ankle joint, and the data of the force plate in the right stance phase were analyzed synchronously with the image data of bare foot movements during free, slow, and fast walking. The following results were obtained:

1. The variables showing significant difference between the young adults and the elderly during both free walking and walking within similar range of speeds were step length, walking ratio, swing velocity, height of toe at heel contact, height of toe at heel contact/lower limb length, angle of trunk at toe off, angular displacement of trunk, angular displacement of knee joint, and angle of ankle joint at heel contact. It was thought that these variables indicate the characteristics of the walking movements for the elderly. In other words, it was shown that the elderly had a smaller step length and walking ratio, later swing velocity, lower height of toe at heel contact (smaller dorsiflexion of ankle joint), smaller range of motion of knee joint, and a smaller movement of trunk during walking.

2. It was shown that the elderly had an extremely large variation between individuals in cadence and angle of ankle joint at heel contact.

3. It was suggested that the younger subjects regulated both the step length and cadence in fluctuation of walking speeds; and that, the elderly regulated mainly in the cadence.

4. It was shown that the elderly had a lower height of toe at heel contact regardless of walking speed.

It is thought that the individual differences of physical function increases as one gets older. Furthermore, it is conceivable that the walking function in the elderly varies between those with extreme reduction and those with almost no reduction. When comparing the walking movements of the young and elderly, it is necessary to pay attention to this point.

The purpose of this study was to investigate the change in kinetics of the lower limb joints in 100 m sprint running. Nine male sprinters, running 100 m with the maximum effort, were videotaped at every 10 m mark from the start to 90 m mark with five high-speed cameras (250 Hz) and five normal VTR cameras (60 Hz). Two dimensional coordinates of the body landmarks were obtained by digitizing VTR images over at least, two steps at every 10 m. Performance descriptors, kinematics and kinetics such as stride length, stride frequency, joint torque and joint torque power of the lower limb joints were calculated by an inverse dynamics approach, with estimating ground reaction forces from the acceleration of the whole body center of gravity. The relationships between changes in running velocity and the joint torque and joint torque power of the leg were analyzed. (1) 100 m sprint could be divided into four phases: the first and second acceleration phases, the maximum speed phase, and the deceleration phase. (2) In the first acceleration phase, 0-30 m, where the stride length and stride frequency increased. There were significant relationships between increases in running speed, stride length, and stride frequency and increases in negative power exerted by knee extensors in the early recovery phase, positive power by hip extensors and negative power by knee flexors in the late recovery phase. (3) In the second acceleration phase, 30-50 m, where the stride length increased and the increase in the running speed was smaller than that of the previous phase. Positive power exerted by hip flexors in the early recovery phase and negative power by knee flexors decreased. (4) In the maximum speed phase, 50-70 m, significant increase in powers to the previous phase were found in positive power exerted by hip flexors in the early recovery phase, negative power by knee flexors in the late recovery phase, and power by plantar flexors during the support phase so as to allow the sprinters to acquire higher speed. (5) In the deceleration phase, 70-100 m, where the stride frequency as well as the running speed decreased. The decreases were found in positive power exerted by hip flexors in the early recovery phase and negative power by knee flexors in the late recovery phase.

These results revealed that the critical factors in the joint kinetics of 100 m sprint running would be power exertions of hip extensors, knee extensors and knee flexors in the late recovery phase for the acceleration, of hip flexors in the early recovery phase, and of knee flexors in the late recovery for high speed and speed endurances.

In the present study, muscle fiber behavior of the medial gastrocnemius (MG) and soleus (SOL) muscles during isokinetic concentric (CON) and eccentric (ECC) plantar flexions were directly measured in vivo. The subjects (n = 6 men) performed maximal voluntary plantar flexions on an isokinetic dynamometer at 60, 120, 180, 240 deg/s, concentrically and eccentrically. With the use of ultrasonography, muscle fiber lengths and pennation angles were determined. From the time course of fiber length changes, muscle fiber shortening and lengthening velocities (V_fiber) were obtained. Considering the effects of pennation angle, muscle shortening and lengthening velocities were also calculated. V_fiber changed as a function of angular velocities [MG: 32-90 mm/s (CON) and 37-97 mm/s (ECC); SOL: 35-81 mm/s (CON) and 37-84 mm/s (ECC)]. However, relative changes of V_fiber were less than those of angular velocities. This result suggests that muscle fiber behavior does not always match joint movement due to muscle-tendon interaction. V_fiber of MG was larger than that of SOL for all test conditions, suggesting inter-muscle differences in muscle fiber behavior during isokinetic movements, but the differences were not evident at the muscle level.

The purpose of this study was to estimate the knee extension torque generated by vastus lateralis (VL) during pedaling on the basis of VL tendon elongation (ΔLt). The fascicle length and pennation angle of VL during isometric knee extensions (0, 20, 60, 100 Nm; 30°, 45°, 60°, 75°, 90°, 105°) were measured using a B-mode ultrasonography (n = 5). ΔLt was estimated from these measurements and the relations between ΔLt, knee joint angle and the knee extension torque generated by VL (TQ) were obtained. ΔLt of the same subjects during pedaling was taken from a previous study. TQ during pedaling was estimated on the basis of ΔLt during isometric knee extensions and pedaling (TQ_ΔLt). TQ during pedaling was also estimated on the basis of the inverse dynamics (TQ_inv). The peak value of TQ_ΔLt (19.8 ± 11.2 Nm) during pedaling was significantly greater than that of TQ_inv (9.3 ± 4.0 Nm) (p < 0.05), which might be related to the lower activation level and the different activation pattern of the rectus femoris compared with those of the VL. The pattern of TQ_inv differed significantly from that of TQ_ΔLt, which might be related to the activation of the biceps femoris that increased in the latter half of the knee extension phase during pedaling. Since the methodology used in this study is non-invasive and measures the parameter that is closely correlated to the joint torque generated by a single muscle, it can be a useful tool for investigating the mechanics of human movements.