Abstract:

During self-induced and externally triggered posture perturbations the central nervous system (CNS) subconsciously activates two different neural control strategies named feed-forward mechanisms (FFM) which is presented as anticipatory postural adjustments (APAs) and feedback mechanisms (FBM) which is presented as compensatory postural adjustments (CPAs). Because of these two neural control strategies the postural muscles can respond rapidly in 50 to 120ms and the center of body gravity can be stable. It is a classic experiment paradigm that observing FFM by APAs changes of postural muscles triggered by optic clues. However, sudden loading and unloading triggered by temporal clues is a new way to examine neuromuscular rapid response control. Its impact on APAs and CPAs of postural and focal muscles during sudden posture perturbation is still unclear and the interaction between optic and temporal clues has not been reported yet. This experiment aimed to examine the effects of the optic and temporal clues on APAs and CPAs by which CNS acts on postural and focal muscles during externally triggered posture perturbation. Sixteen healthy young adults were subjected to the classic ball hitting test (BHT) in six conditions combined by optic clues (eyes open and eyes closed) and temporal clues (no counting backwards for release, counting backwards of release by the experimenter and counting backwards by subjects themselves). EMG activity on right side musculus biceps brachii as focal muscle and right side lumbar erector spinae and lumbar multifidus as postural muscles was collected. The incidence of APAs, the latency of pre-activation and the response intensity of CPAs of the muscles mentioned above were calculated in order to reflect the effects of perceptual clues on APAs and CPAs of postural and focal muscles. Our results showed that the incidence of APAs of postural and focal muscles was significantly increased and the pre-activation of postural and focal muscles was significantly earlier with optic clues than without. Besides, optic clues significantly decreased the response intensity of CPAs of the focal muscle. Nevertheless, temporal clues primarily induced earlier pre-activation of the focal muscle without significant effects on APAs or CPAs of postural muscles. We conclude that the effects of optic and temporal clues on CNS motor control of postural and focal muscles during externally triggered posture perturbation are different. Optic clues have significant effects on APAs of postural and focal muscles and CPAs of the focal muscle, which suggests a pre-activation superiority for optic clues. Temporal clues only have significant effect on APAs of focal muscles.

Key words: optic clues, temporal clues, anticipatory postural adjustments, compensatory postural adjustments, externally triggered postural perturbation