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The Balance Recovery Mechanisms Against Unexpected Forward Perturbation


Falls are one of the main concerns of the elderly. Proper postural adjustments to maintain balance involve the activation of appropriate muscles to produce force and to relocate the center of body mass (CoM). In this study, biomechanical aspects of dynamic postural responses against forward perturbations were experimentally determined by simultaneous measurements of joint angles and EMG activations. Thirteen young and healthy volunteers took turns standing on a flat platform, and were directed to move in the forward direction by an AC servo-motor set at two different speeds (0.1 and 0.2 m/s). Joint motions were recorded, and they followed the sequence of ankle dorsiflexion, knee flexion, and then hip flexion during the later acceleration phase (AP) in order to maintain postural balance against forward perturbation. Tibialis anterior for the ankle dorsiflexion and biceps femoris for the knee flexion were activated during the second half of the AP as the primary muscles to recover balance. In addition, gastrocnemius, which was related to ankle plantarflexion, and rectus femoris, which was related to knee extension, were activated to maintain balance. Movements of the center of plantar pressure and ground reaction forces in fast-speed perturbation were significantly larger than those in slow-speed perturbation. As a result, the ankle strategy was used for slow-speed perturbation, but the mixed strategy consisting of both ankles and hip were used for fast-speed perturbation.

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This research project was supported by the Sports Promotion Fund of Seoul Olympic Sports Promotion Foundation from Ministry of Culture, Sports and Tourism and also was financially supported by the Ministry of Education, Science Technology (MEST) and Korea Industrial Technology Foundation (KOTEF) through the Human Resource Training Project for Regional Innovation.

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Correspondence to Youngho Kim.

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Hwang, S., Tae, K., Sohn, R. et al. The Balance Recovery Mechanisms Against Unexpected Forward Perturbation. Ann Biomed Eng 37, 1629–1637 (2009).

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  • Forward perturbation
  • Dynamic postural responses
  • Motion analysis
  • EMG onset
  • Ankle strategy
  • Mixed strategy