This study aimed to compare the muscle activities of the lower limb during overground level running (LR) and uphill running (UR) by using a musculoskeletal model. Six male distance runners ran at three running speeds (slow: 3.3 m/s; medium: 4.2 m/s; and high: 5.0 m/s) on a level runway and a slope of 9.1% grade in which force platforms were mounted. A musculoskeletal leg model and optimization were used to estimate the muscle activation and muscle torque from the joint torque of the lower limb calculated by the inverse dynamics approach. At high speed, the activation and muscle torque of the muscle groups surrounding the hip joints, such as the hamstrings and iliopsoas, during the recovery phase were significantly greater during UR than during LR. At all the running speeds, the knee extension torque by the vasti during the support phase was significantly smaller during UR. Further, the hip flexion and knee extension torques by the rectus femoris during UR were significantly greater than those during LR at all the speeds; this would play a role in compensating for the decrease in the knee extension torque by the vasti and in maintaining the trunk in a forward-leaning position. These results revealed that the activation and muscle torque of the hip extensors and flexors were augmented during UR at the high speed.

The purposes of this study were to determine the joint torque (JT) and power (JP) of the takeoff leg and the relationship of the angular impulse and work done by the JTs to center of gravity (CG) velocity change during the long jump takeoff, and to identify the functions of the takeoff leg joints. The takeoff motion of eleven Japanese male long jumpers was videotaped (250 Hz) from the right side of the runway. Ground reaction forces were also recorded (1 kHz). The forward-backward component of the force platform was set parallel to the runway. The plantar-fl exors and knee extensors exerted great negative JP during the fi rst phase and positive JP during the second phase, and, thus, they functioned as great mechanical energy absorbers in the fi rst phase and as mechanical energy generators in the second phase. The hip joint exerted extension torque immediately after touchdown and supported the body against the impact force and contributed to an increase in vertical CG velocity by pivoting the body over the takeoff foot during the fi rst phase. There were no relationships of the magnitude of the peak joint torques of the takeoff leg and angular impulse and work of the takeoff leg joint torques to horizontal CG velocity at touchdown or jumping distance.

The purpose of this study was to investigate kinetic characteristics such as ground reaction forces (GRFs) and joint torques of the lower limb joints in downhill running for distance runners on overground. Six male distance runners were asked to run at three running speeds (3.3, 4.2, and 5.0 m/s) on the slopes of different grades (0, -3.2, -6.4, and -9.1 %) in which two force platforms were mounted. A two dimensional link model was used to calculate joint torques and joint powers of the lower limb joints. In spite that the downward velocity of the CG at the foot contact increased consistently as the grade increased, the impact peak of vertical GRF and the peak loading rate defi ned as maximum rate of change of the vertical GRF did not increase consistently as the grade increased. The runners on steep downhill conditions would be able to avoid excessive impact load by contacting with the ground in more extended hip position and increasing knee fl exion velocity after the foot contact. The negative power of the knee after the foot contact was larger for -9.1 % downhill than the level condition, which revealed the eccentric load on the knee extensors increased in the steep downhill condition. The hip extensors exerted negative power with hip fl exion just after the foot contact in -6.4 and -9.1 % downhill conditions so that the runners could absorb the impact force and mechanical energy.

This study analyzed the joint torque and the mechanical energy flow in the support legs of skilled male race walkers. Twelve race walkers were videotaped using a high-speed camera at a frame rate of 250 Hz set perpendicular to the sagittal plane of motion; their ground reaction forces were measured with two force platforms. A two-dimensional, 14-segment, linked model was used to calculate the kinetics of the support leg joints. In the initial part of the support phase, the mechanical energy flowed into the thigh and shank by the torque of the large hip extensors and knee flexors. In the middle part, the mechanical energy generated by the torque of the large plantar flexors flowed to the foot and from the foot to the shank by the ankle joint force. The mechanical energy flow by the forward joint force of the support hip was significantly related to the walking speed in the final part of the support phase. Our findings suggest that race walkers in the final part of the support phase should exert the torque of the knee extensors and hip flexors to transfer the mechanical energy more effectively to the support thigh and shank.

The aim of this study was to establish the functions of the support leg in the long jump take-off with a three-element mechanical model spring, damper, and actuator The take-off motions of eleven male long jumpers, with personal bests from 6.45 to 7.99 m, were videotaped at 250 Hz and ground reaction forces were simultaneously recorded at 1 kHz. A two-dimensional 14-segment linked model was used to collect basic kinematic parameters. The spring, damper and actuator forces were determined from the displacement and velocity of the centre of mass and from ground reaction forces. Large spring and damper forces were exerted, and absorbed the impact force immediately after the touch-down. The spring force was also exerted from 25 to 75% of the take-off phase. The actuator force was dominant in the latter two-thirds of the take-off phase. Statistically significant correlations were found between the spring force impulse and the knee flexion during the take-off phase (r = 0.699, p < 0.05), and between the knee flexion and the angular velocity of the thigh at the touch-down (r = 0.726, p < 0.05). These results indicated that the jumper should retain less flexion of the take-off leg knee to increase the spring force, after a fast extension of the hip, and use a more extended knee at the touch-down to prevent excessive knee flexion.