Abstract:

In response to sudden posture perturbation, two different neural control strategies in central nervous system are used, named anticipatory postural adjustments (APAs) and compensatory postural adjustments (CPAs). Previous studies have identified associations between psychological expectations of posture perturbation and the intensity of APAs and CPAs. However, it's unclear whether these associations are consistent with different experiment paradigm and perturbations from different sources. This study aimed to examine the psychological predictive effect of sudden posture perturbation magnitude on the APAs and CPAs by which CNS acts on focal muscles and lumbar posture muscles. Arm-raising test and Ball-hitting test were performed with surface electromyography signal analysis. 20 healthy subjects voluntarily participated in the studies. In the Arm-raising test, they rapidly raise arms with a load of 0 kg/1 kg/2 kg in both hands. In the Ball-hitting test, they caught a ball fell from eye level to the pan holding in their hands. The ball weights of 1 kg/1.5 kg/2 kg were used. EMG activities of biceps brachii (BB) as focal muscle, lumbar erector spinae (LES) and Lumbar multifidus (LMF) as posture muscle were recorded. The pre-activation time and integrated EMG of APAs and CPAs were calculated to determine the effects of perturbation magnitude from different sources on APAs and CPAs of focal and postural muscles. The results showed that the posture perturbation magnitude had a psychological predictive effect on muscles under both internal and external perturbation conditions. Under the internal perturbation condition, the APAs IEMG of BB significantly increased with the magnitude of perturbation, while the APAs IEMG of LES and LMF were different only between 0 kg load level and the other two. The pre-action time and CPAs IEMG of all these muscles have no significant different under all 3 load levels. Under the external condition, the expectation of perturbation magnitude has significant effect on the pre-action time of both BB and LMF, as well as the APAs IEMG of BB, LES and LMF. The APAs IEMG of BB and LMF were significant different between 3 load levels, while the pre-action time of BB and LMF, and the APAs IEMG of LES had no difference between 1.5 kg load and 2 kg load. Perturbation magnitude expectation had no effect on the CPAs IEMG on all 3 muscles. We conclude that psychological predictive effects of posture perturbation are existed on both posture and focal muscle activities. Such effects are exhibited differently depending on internal and external perturbation conditions. CNS will orchestrate to give an optimal control of postural muscle through adjustments of APAs IEMG under internal condition, or though adjustments of both pre-action time and APAs IEMG under external condition. The observed effects on APAs and CPAs suggest that the psychological predictive effect of sudden posture perturbation magnitude comes mainly from the CNS modulation on APAs mechanism.

Key words: psychological predictive effect, perturbation magnitude, anticipatory postural adjustments, compensatory postural adjustments