Keeping your balance while balancing a cylinder: interaction between postural and voluntary goals

Abstract

The present study investigated whether postural responses are influenced by the stability constraint of a voluntary, manual task. We also examined how task constraint and first experience (the condition with which the participants started the experiment) influence the kinematic strategies used to simultaneously accomplish a postural response and a voluntary task. Twelve healthy older adults were perturbed during standing, while holding a tray with a cylinder placed with the flat side down (low constraint; LC) or with the rolling, round side down (high constraint; HC). Central set changed according to the task constraint, as shown by a higher magnitude of both the gastrocnemius (GAS) and tibialis anterior (TA) muscle activation bursts in the HC than the LC condition. This increase in muscle activation was not reflected, however, in changes in the center of pressure or center of mass displacement. Task constraint influenced the peak shoulder flexion for the voluntary tray task but not the peak hip flexion for the postural task. In contrast, first experience influenced the peak hip flexion but not the peak shoulder flexion. These results suggest an interaction between two separate control mechanisms for automatic postural responses and voluntary stabilization tasks.

Transfer of postural adaptation depends on context of prior exposure

“…They found that subjects used a characteristic control strategy in each condition; interestingly, they also found that when subjects transferred from one condition to the other, they initially used an intermediate control strategy before adapting the characteristic strategy of the new condition. In two other studies, de and Papegaaij et al (2012) studied the effects of voluntary task stability constraints on reactive postural control. Subjects stood on a platform and held a tray (voluntary task) with a half-cylinder placed flat side down (low stability constraint) or round side down (high stability constraint) and were perturbed with backward surface translations (postural task).…”

Postural adjustments to support surface perturbations during reaching depend upon body–target reference frame

“…In conclusion, as Trivedi et al (2010) and Papegaaij et al (2012) have also demonstrated, we have shown that a significant interaction between the feed-forward adjustments of posture required to complete a reach movement while standing and the feedback adjustments of posture needed to correct for an unexpected perturbation. This study has provided further evidence, however, that the precise nature of this interaction depends upon body-target interaction with both target reference frame and time of platform perturbation playing a significant role in the modulation of postural activity.…”

Efeito de diferentes tipos de tarefa suprapostural em respostas posturais reativas a uma perturbação mecânica

“…É provável que a avaliação do centro de pressão realizada não seja uma medida sensível para ser utilizada em estudos com este tipo de perturbação de equilíbrio. No estudo realizado por Papegaaij et al (2012) também se verificou uma situação em que as diferenças verificadas em termos musculares, entre as condições de alta e baixa restrição, não se refletiram em modificações importantes do centro de pressão ou do centro de massa .…”