The role of horizontal component of the ground reaction force (GRF) in the motion control of vertical jump was investigated. Eight male subjects performed two types of counter movement jump. One was free maximal-effort counter movement jump (Type F). The other was the maximal-effort counter movement jump, with heels kept off the floor (Type H). In this case, contact between the foot segments and the floor was restricted. GRF was recorded with a force platform. Location of the center of pressure (COP) and movement of mass center of body (MCB) were calculated. In both types, negative (anterior-posterior direction) value of horizontal component of GRF was observed just before the take-off. For both MCB and COP, horizontal movement was larger in Type F than in Type H. In order to jump vertically, MCB has to be located mechanically just above COP at the instant of take-off. As the negative horizontal force acted on the MCB and stopped its forward motion just before take-off especially in Type F, the location of the COP and the MCB were consequently synchronized at the take-off. There is a possibility that assumptions about the interface between foot and ground, presented in preceding simulation studies are somehow simplistic.

The role of bi-articular rectus femoris (RF) in motion control and energy transportation was investigated in jumping motions. Standing broad jumps (BJ) and vertical jumps (VJ) of six male subjects (mean body height 1.71 m, mean body mass 62.8 kg) were analyzed by inverse dynamics. Length of muscle tendon complex (MTC) was estimated for RF and mono-articular vastus medialis (VM), from joint angles. Surface EMG signals were recorded from RF and VM. These values were compared between BJ and VJ. Mechanical energy (sum of potential and translational kinetic energy) that provided to the mass center of body (MCB), by the instant of take off was not significantly different between BJ (301 J) and VJ (308 J). Angular velocity of head, arms and trunk segment was larger in BJ (4.06 rads^-1) than in VJ (1.86 rads^-1) , at the instant of take off. Hip extension was more freely executed in BJ than in VJ. Longer eccentric phase of RF MTC was observed in BJ than in VJ, which suggested that muscle force of RF was lower in BJ. Larger EMG activity was observed for RF in VJ than in BJ (ratio of peak value of low pass filtered signal, VJ/BJ=1.50). This difference could not be observed for VM. Contribution of hip joint in total positive work was larger in BJ (55%) than in VJ (44%), whereas contribution of ankle joint was larger in VJ (33%) than in BJ (24%). These data supported the hypothesis that the action of RF controlled the rotational motion of HAT segment, at the same time transferring the mechanical energy from hip to knee joint.

Relationships between provision of mechanical work output from individual joints and jump height in vertical jumps were discussed in this study. Seven male subjects performed 12 sub-maximal to maximal effort squat jumps. Ground reaction force and motion of five anatomical landmarks were recorded and processed by inverse dynamics. Net joint power and work were calculated for ankle, knee, and hip joints, and normalized by the body mass. They were summed and defined as total work output. There were strong linear relationships between jumping height and ankle joint work, and jumping height and total work (r=0.902 and 0.946, respectively). For hip and knee joints, linear relationships were low (r=0.662 and 0.275, respectively). It was found that proportion of the provision of mechanical work output from individual joints varied greatly among subjects. These results implied that pattern-jumping motion was subject specific.

This study was designed to investigate the relationship of the body's center of gravity (CG) and the joint torque of rhe lower extremities during take-off movement with different initial postures in the jump. Three initial postures were employed: an unconstrained posture (N), posture with head+arms+trunk (HAT) segment perpendicular to the ground (L) and posture with the HAT segment parallel to the ground (T). The experiment consisted of two stages. In the first stage, one subject executed jumps using maximal effort with the three initial postures. Joint torque was calculated by the inverse dynamics approach method. In the second stage, computer simulation was executed by inputting manipulated joint torque amplitude. The kinematics of the CG as calculated in the simulated jumps were compared among N, L, and T postures. In comparison of L and N postures, with the L posture the ratio of work at the knee joint was increased and the knee and ankle joint had no relationship with the horizontal velocity of the CG. The relationship between the knee and ankle joint was highly negative. The increase of ankle joint torque was strongly related to the increase of the vertical velocity of the CG. In comparison of the T and N postures, with the T posture the ratio of work at the knee joint was decreased and the ankle joint demonstrated no relationship with the horizontal velocity of the CG. Other relationships were same as with N. The N posture was more flexible in response to the change of torque amplitude than the other postures.

The purpose of this study is to clarify the effects of differences in center-of-gravity (CG) of a backpack on joint moment-of-force during walking. On three different occasions, six male subjects walked on a straight platform at a voluntary speed. During walking, they randomly shouldered a backpack which had a different position of CG, that was about 88% height (HP) or 72% height (MP) or 55% height (LP), respectively. The motion and ground-reaction-force were measured by high speed video and force platform analysis. The following results were obtained:

1) The moment-of-force produced by the weight of HAT (head & arm & trunk) with a backpack acted on the forward rotation of the upper body during walking. And that in the higher position was significantly larger than that in the lower.

2) The hip extension and abduction moment-of-force in the higher was significantly larger than that in the lower.

3) The maximal angle of forward tilting during walking in the lower was significantly larger than that in the higher.

4) The walking speed in the higher was significantly larger than that in the lower.

Therefore, we consider that the higher CG of backpack may increase biomechanical efficiency during walking. However the higher CG backpack may act large stress on hip extensor and abductor muscles.

The purpose of this study was to construct an estimated equation that would reveal the relationship during walking between supporting time obtained by analysis of ground reaction force and walking speed, step length and cadence obtained by image analysis. Five healthy young men, five healthy elderly men, six healthy young women, and twenty healthy middle aged women participated as the subjects in this study. The data of the force plate at stance phase were analyzed in synchronization with the image data during walking. The following results were obtained:

1. It was indicated that walking speed, step length and cadence can be determined only by the data of supporting time obtained through analysis of ground reaction force, given the linearized relationship between walking speed and step length, and that between supporting time and step duration. Furthermore, the precision of estimation can be improved by including the effect of height.

2. The validity of the above estimated equation was evidenced as a consequence of verification with a different group (ten healthy young men and ten healthy elderly men).

3. The following were the estimated equations obtained from all the data including those used for verification. These equations determine walking speed (v) , step length (l) and cadence (ca) by supporting time (t_sup) and height (ht).

v = 60 (bht + c)/(dt_sup + e - 60a)

l = 60a (bht + c)/(dt_sup + e - 60a) + bht + c

ca = 60/(dt_sup + e)

provided that a = 0.004092, b = 0.001579, c = 0.091408, d = 0.707010, e = 0.065543

In conclusion, it may be shown that the estimated equation in this study was able to estimate with high precision within the limits of application.

The purpose of this study was to identify functions of the torso and lower limbs in baseball pitching. Pitching motions of ten baseball players were analyzed by three dimensional motion analysis method with two high-speed video cameras (200 Hz) and two force platforms. Three dimensional coordinates of body segment endpoints were obtained by a DLT technique, and ground reaction forces acting on the pivot and stride legs were sampled at 250 Hz and synchronized with the coordinate data. Major variables computed were the joint torques, joint torque powers, and works done by the torso, hip, knee and ankle joints.

Forward twisting torque of the torso was exerted during the twisting phase (from the starting of torso twist, TS, to the stride foot contact with the ground, SFC), and increased up to it's peak during early cocking phase (from SFC to the instant of the minimum ball velocity, Min. BV), in which joint angular velocity of twisting changed from backward to forward direction and as a result the negative joint torque power changed to positive direction. During late cocking phase (from Min. BV to the instant of the maximum external rotation of the shoulder, MER), the torso exerted the torques of extension, backward twisting and left bending and the negative powers.

The hip and knee joints of the pivot leg exerted the extension torque and the ankle joint exerted plantar flexion torque before SFC, but their joint torque powers were not so large as expected. During the second half of the twisting phase, the positive joint torque power of hip extension for the pivot leg rapidly increased.

After SFC, the hip joint of the stride leg exerted the extension torque, the knee exerted flexion torque, and the ankle joint showed the plantar flexion torque. Negative power by the hip extension torque was the greatest in the stride leg joints.

Large moment about the vertical axis of the lower torso was due to the hip extension torque of the pivot leg during twisting phase and the hip adduction torque of the stride leg during early cocking phase.

Works done by the torso and hip joint torques during pitching phase (SFC to REL) were much larger than those of the knee and ankle joints, although there were no significant relationships between the ball velocity and works done by the torso and hip joints.

These results suggest that one of the major functions of the torso and legs is not to directly increase the ball velocity but to exert joint torques and powers for the twisting of the torso and for the generating mechanical energy to transfer to the throwing arm and the ball.