Role of hand contact in continually challenged postural equilibrium

Balance is defined as the ability to maintain postural stability (equilibrium) during quiet standing, perturbed standing and voluntary movement. Additional hand contact helps in retaining balance by extending the base of support. Little is known, however, about the actual contribution of the hand support in a continually challenged stability during standing. With this study we aimed to investigate the activity of hand contact when balance was challenged by a force perturbation applied to the waist, to determine to what extent balance corrective responses are generalized across continuous perturbation. We measured the muscle activity of right shoulder, trunk and right lower leg following application of a mild, random and continuous forward and backward pulls at the waist. Results show that in situations with additional hand support, the contribution of lower leg muscles was minimized and suggests that the postural equilibrium was dominantly obtained by the use of hand muscles. Interestingly, the activation of the trunk flexors remained unchanged where the activation of trunk extensors rose significantly in cases where the subjects used the additional hand support.