The purpose of this study was to identify the control mechanism of changing movement of the body's center of mass (CM) during standing up from a chair. One of the requirements of stand-up motion from a chair is that the movement of the CM must be controlled from forward horizontal direction to upward vertical direction, in order to secure upright balance at the termination of the standing. The CM trajectory and velocity for stand-up motion were computed at three movement speeds (natural, fast, and slow) by a motion analysis system (VICON). Eleven events were identified in each trial. The main events were the time of the peak propulsive power and the peak braking power, the time of the peak horizontal component of the CM velocity occurrnce, and the time from the beginning to the completion the body losing contact with the seat. The timing and sequence of these events were investigated. The results showed that the peak propulsive power in the slow speed group had the earliest timing and in the fast group had the latest at the beginning and at the completion of the body losing contact with the seat. There were statistical significant differences in the sequential times compared with the other group of events. The feature of the timing of events suggests that the control mechanism of changing movement of the CM is produced by the braking power progressively increasing before the time the subject leaves the seat. The timing of these events varied with the conditions of standing up from the chair.
The purpose of this study was to investigate whether a chosen movement pattern was organized depending on a goal-oriented task. [Subjects] Eleven healthy adults aged 25 to 35 years (median 28 y) and 10 frail, community-dwelling older persons 67 to 86 years (median 77 y) participated. [Methods] Subjects were videotaped standing up from a supine position repeatedly, for 20 times. The goal-oriented task was several steps toward a goal following rising. Movement patterns of three body regions were used to classify the videotaped performances. The data collection was performed by a VanSant(1988). [Results] There was consistency of the movement pattern and a decrease in movement pattern items in the goal-oriented task of the older group. [Conclusion] It is important to clarify the factors with which the combination of movement patterns was organized.
The purpose of the study was to examine the changes in soleus Hoffmann (H)reflex and volitional (V)-wave after resistance training (RT) with and without neuromuscular electrical stimulation (NMES). Fourteen participants were randomly allocated to receive RT with NMES (RT+NMES, n = 7) or RT without NMES (RT, n = 7). Each participant trained for 10 sessions of right leg standing calf-raise for 2 weeks. For the RT+NMES group, NMES was applied to the tibial nerve using rectangular pulses (400 µsec duration, 75-Hz trains). Stimulation intensity was set at the maximal tolerable level. The H-reflex was elicited just above motor threshold during rest and during maximal voluntary isometric contraction (MVIC) conditions. The H-reflex and V-wave were normalized to the maximal motor response (Mmax). There was a significant interaction between time (pre/post) and group in the H-reflex during rest and during the MVIC condition (P = 0.05), but no significant difference in plantar torque, Mmax or Vwave. The H-reflex during rest decreased from 0.54 to 0.38 in the RT+NMES group (P = 0.01) but did not change in the RT group (from 0.48 to 0.47, P = 0.79). During MVIC, the H-reflex increased from 0.23 to 0.76 in the RT+NMES group (P = 0.02), but did not change in the RT group (from 0.44 to 0.58, P = 0.12). The results indicate that NMES-induced proprioceptive input during RT has an inhibitory effect in the resting muscle and an excitatory effect in the voluntarily activated muscle via spinal and/or supraspinal pathways.
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