Relationship between hip abductor strength, rate of torque development scaling factor and medio-lateral stability in older adults

Abstract

Background: Recently, the rate of torque development scaling factor (RTD-SF) has been proposed as a useful tool that could contribute to a more comprehensive insight into muscular capacity. While lower RTD-SF is associated with ageing and certain neuromuscular diseases, it remains unknown whether this novel measure is associated with the postural control in the older adults.

Research question: Are hip abductor muscle strength, RTD and RTD-SF associated with responses to external postural perturbations in medio-lateral direction in older adults?

Methods: Twenty healthy older adults (14 females, 6 males) were assessed for hip abductor muscle strength, RTD and RTD-SF, using a custom-built dynamometer. Perturbations were applied at waist level (4 perturbation intensities, 15 repetitions each) using a wire-pull paradigm, with centre-of-pressure (CoP) being recorded with force plates. For each condition (i.e. perturbation intensity), medio-lateral displacement and velocity of the CoP were computed. For both parameters, within-individual variation (representing consistency of the responses), expressed by the standard deviation (SD) of CoP parameters was also considered. Pearson correlation coefficients were computed between parameters of hip muscle capacity and CoP responses and SD values of CoP responses.

Results: RTD-SF was moderately positively related to the consistency of the responses of both CoP displacement and velocity (r = 0.53-0.56; p = 0.011-0.016) at the lowest level of the perturbation magnitude (15 N). No other statistically significant relationships were found (all r < 0.35).

Significance: RTD-SF could play a role in preserving postural balance in older adults when low-intensity perturbations are applied. RTD-SF is a novel outcome measure that could represent an important alternative clinical tool to traditional strength assessments. It could represent a supplementary tool to assess the risk of falls, however, several limitations and ambiguities need to be resolved by future research before it can be utilized in practice.

Keywords: Elderly; Motor control; Muscle quickness; Muscle response; Stability.