Age-related changes in rate and magnitude of ankle torque development: Implications for balance control

Background. One of the key components of postural control is the motor syst em's ability to produce appropriate torques to counteract perturbations tha t may lead to a loss of balance. Evidence exists to show that there is an a ge-related decline in absolute strength and in the ability to rapidly produ ce torque. The relationship between age-related decreases in these voluntar y torque production capabilities and the ability to rapidly produce torques in a reactive balance task has not been studied. Thus, the purpose of this study was to examine the magnitude and rate of torque production in younge r and older adults under reactive balance conditions. Methods. Older (OA) and younger (YA) adults received forward and backward s upport surface translations of varying amplitudes and velocities. Maximum a nkle muscle torque (maxMa) and rate of change of ankle muscle torque (Ma) f ollowing a perturbation were calculated. Results. Two balance responses emerged: a no-step and a step response. With increasing perturbation difficulty, YA and Oh used different responses. Th e no-step and step responses were examined For age-group differences in the force characteristics. No significant age-group differences were found for maxMa or rate of change of hla within either no-step or step responses. Conclusion. The results of this study suggest that neither the magnitude no r rate of ankle muscle torque production, as produced during the initial ba lance response in this set of reactive balance control tasks, determines th e different balance responses seen in younger versus older adults.