The Effects of Attentional Focus and Stance Pattern on soleus H Reflex: Age-related Differences
Date Issued
2015
Date
2015
Author(s)
Lei, Weng-Hin
Abstract
Background and Purpose: Focus of attention has been reported as a critical factor for motor control. When performing a motor task, attention could be directed to the action itself (internal focus, IF) or to the effect of the action (external focus, EF). Most previous studies believed that EF strategy is superior to IF strategy with a “reflex-type control” mode. However, some researchers proposed worse performance of internal focus control may result from inappropriate instruction. Besides, both postural difficulty and aging effects are also the important factors for attentional focus control. And there is insufficient evidence for “reflex-type control” of EF strategy. The purpose of this study was to investigate the effects the attentional focus on motor and postural performance and its related neuromuscular activities under stable and unstable stance between young and old adults. Methods: Fifteen younger healthy (mean age: 23.87 ± 2.61) and fifteen elderly healthy (mean age: 66.73 ± 3.97) adults were recruited in this study. With an electrogoniometer and acrylic plate attached on right elbow joint and forearm respectively, participants were requested to perform a motor tracking task with directing their attention to elbow movement (IF) or to plate movement (EF) when standing on a stable or unstable surface. Tracking error and jerk, postural sway amplitude and approximate entropy (ApEn), soleus H-reflex, and EMG co-contraction activity of soleus and tibialis anterior were measured. Result: For the behavior performance, tracking error suggested that there were significant main effects of attentional focus (F1,28 = 83.04, p < .01), with less tracking error in the IF conditions. For the smoothness of tracking trajectory, jerk square mean did not vary with attentional focus, posture difficulty, or age difference. In regard to postural performance, decreased postural sway and increased ApEn with EF strategy were observed for both younger and older adults. For electrophysiological findings, H/Mmax ratio and co-activation index were modulated by attentional focus with larger H/Mmax in the younger group and smaller co-contraction index in the EF conditions for both groups. On the other hand, EMG activity of biceps brachii was smaller when adopting an EF strategy to perform the tracking task in the older adults (p < .05) but not in the young adults (p > .05). Conclusion: This study showed that both attentional focus and postural task difficulty influence the performance of a posture-suprapostural task between younger and older healthy adults. For a continuous tracking task, IF might be a better control strategy than EF. Based on H-reflex results, the hypothesis of “reflex-type control” for EF strategies was evidenced in younger adults. The results of the present study could be applied on older adults for providing adequate control strategy while performing a postural-suprapostural task. Further studies would be needed to be confident in these conclusions for patients with neurological disease.
Subjects
attentional focus
postural balance
H-reflex
age effect
Type
thesis
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