Context-dependent reflex control: some insights into the role of balance.
Recent research suggests that the balance requirements of a task dictate the reflexive response. However, these observations were inferred indirectly from either different tasks or different phases of the same task. This study directly tested the hypothesis of balance-dependent control during recovery from an unexpected trip. The subjects were tripped in two different support conditions: unilimb support (provided by the stance limb) or trilimb support (provided by the stance limb and both arms placed on adjacent parallel bars). The subjects exhibited anticipatory changes: they biased the body center of mass toward the support limb in the mediolateral direction and elevated the swing limb higher when there was a possibility of being tripped. The electromyographic (EMG) latencies were not influenced by the threat to equilibrium. The magnitudes of the EMG reflexive response to the trip were clearly modulated as a function of the threat to stability, not in a simple manner, but rather in a complex manner, which optimized the recovery strategy. It is evident that the overriding concern, equilibrium control during locomotion, has a dominant influence on reflex modulation.
Rietdyk
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Department of Kinesiology, University of Waterloo, Ontario, Canada.
Patla
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D000222:Adaptation, Physiological / Q000502:physiology; D000328:Adult; D004576:Electromyography; D006801:Humans; D008297:Male; D009068:Movement / Q000502:physiology; D009132:Muscles / Q000502:physiology; D004856:Postural Balance / Q000502:physiology*; D012018:Reflex / Q000502:physiology*