Kei Masani

Reciprocal angular acceleration of the ankle and hip joints during quiet standing in humans

Abstract.Human quiet standing is often modeled as a single inverted pendulum rotating around the ankle joint, under the assumption that movement around the hip joint is quite small. However, several recent studies have shown that movement around the hip joint can play a significant role in the efficient maintenance of the center of body mass (COM) above the support area. The aim of this study was to investigate how coordination between the hip and ankle joints is controlled during human quiet standing. Subjects stood quietly for 30xa0s with their eyes either opened (EO) or closed (EC), and we measured subtle angular displacements around the ankle (θa) and hip (θh) joints using three highly sensitive CCD laser displacement sensors. Reliable data were obtained for both angular displacement and angular velocity (the first derivative of the angular displacement). Further, measurement error was not predominant, even among the angular acceleration data, which were obtained by taking the second derivative of the angular displacement. The angular displacement, velocity, and acceleration of the hip were found to be significantly greater (P<0.001) than those of the ankle, confirming that hip-joint motion cannot be ignored, even during quiet standing. We also found that a consistent reciprocal relationship exists between the angular accelerations of the hip and ankle joints, namely positive or negative angular acceleration of ankle joint is compensated for by oppositely directed angular acceleration of the hip joint. Principal component analysis revealed that this relationship can be expressed as:

Fractal correlation of initial trajectory dynamics vanishes at the movement end point in human rapid goal-directed movements

ddot theta _h = gamma ddot theta _a

EMG activities of mono- and bi-articular muscles during goal-directed ballistic movement

n with γ=–3.15±1.24 and γ=–3.12±1.46 (mean ±SD) for EO and EC, respectively, where

Difference in aftereffects following prolonged Achilles tendon vibration on muscle activity during maximal voluntary contraction among plantar flexor synergists

ddot theta

StanceAnkle Extensor Activities During Quiet Importance of Body Sway Velocity Information in

n is the angular acceleration. There was no significant difference in the values of γ for EO and EC, and these values were in agreement with the theoretical value calculated assuming the acceleration of COM was zero. On the other hand, such a consistent relationship was never observed for angular displacement itself. These results suggest that the angular motions around the hip and ankle joints are not to keep the COM at a constant position, but rather to minimize acceleration of the COM.

sustained contraction in relation to alternate muscle activity during low-level Local blood circulation among knee extensor synergists

Abstract. Isometric unilateral elbow extension training was conducted for 10xa0weeks (3 times per week) on 12 young adult men to investigate the effects of equivolume exercise programs with different combinations of intensity and duration on the morphological and functional aspects of the triceps brachii muscle. One group of 6 subjects trained by developing maximal voluntary contraction (MVC) for 6xa0s per set with 12 sets per session (100%G), while the other group of 6 subjects trained at 60% of MVC for 30xa0s per set with 4 sets per session (60%G). Training significantly increased the muscle volume (Vm), fascicle pennation angle of the triceps brachii, and torque output during concentric and eccentric elbow extensions at three constant velocities of 0.52, 1.57, and 3.14xa0rad·s–1 as well as under the training condition, with no significant differences in the relative gains between the two programs. However, 100%G showed significantly greater Vm than 60%G after training, when Vm before training was normalized. Thus, only 60%G significantly increased the ratio of torque to Vm developed in the eccentric actions at the three velocities and concentric action at 1.57xa0rad·s–1. The present results indicate that isometric training programs of medium resistance/long duration and high resistance/short duration produce different effects on Vm and dynamic strength relative to Vm, even if the training volume is equalized between the two protocols.