Changes in postural control during a repetitive reaching task

Abstract

Background: A reaching movement is an important action in daily life. When a reaching movement is directed to a target placed at a distance greater than arm length in standing, a driving or braking force must be created to initiate and to terminate whole body movement (Tyler and Karst, 2004). Therefore, the central nervous system activates postural muscles at an appropriate timing and subsequent initiates joint motion in lower limb. Though it is well known that motor components such as the peak velocity of arm movements improve through reaching training, it remains unclear how postural components improve. Purpose: The repeated reaching training is widely adopted as one of rehabilitation programs on a clinical treatment. However, changes in postural control during reaching training have been rarely reported. Therefore, the purpose of this study is to investigate change in muscle activity and joint angle of lower limbs through repeated reaching training in standing posture. Methods: Fifteen healthy subjects (23± 2 years) participated. All subjects provided written informed consent, as approved by the ethics committee of Hokkaido University Faculty of Health Sciences. Subjects performed reaching to a small target placed in the nearly maximum reach distance as quickly as possible. One hundred trials of reaching with right arm were repeated for three consecutive days and they were examined again after discontinuing training for one day. The surface electromyography (EMG) of tibialis anterior (TA) and gastrocnemius (GAS) was recorded. Kinematic data were collected using a three-dimensional motion analysis system. The integrated EMG (IEMG) were calculated for driving phase (from the reaching onset to the time when hand velocity was maximal) and braking phase (from the time when hand velocity was maximal to termination time of reaching). Hip, knee, and ankle joint angles were calculated. Mean value of the parameters in the first 10 trials on the first training day were compared with those of the other 10 trials on the first training day, and with those of the first 10 trials on the other training day using one-way repeated measure ANOVA and a post-hoc test. The significance level was set at p< 0.05. Results: On the first day, the normalized IEMG of the right TA in driving phase (p< 0.01) and the left GAS in braking phase (p< 0.01) significantly increased through repeated reaching training. Also, the maximum ankle dorsiflexion angle in driving phase (p< 0.05) and the maximum hip flexion angle in braking phase (p< 0.05) significantly increased. Training effects on these parameters were retained after a two-day rest period. Conclusion(s):We found that changes in postural control occurred in both driving and braking phase during a repetitive reaching task. Training effects were retained after subjects discontinued training. These results suggest postural learning not only to initiate thewhole body forwardmovement but also to terminate the movement occur during a repetitive reaching task. Implications:A better understanding of the postural control mechanism during repetitive reaching training is useful for physical therapy practices.