Title

Posture and movement interactions during rhythmic unipedal stepping in young, middle-aged and older adults

Date of Completion

January 2006

Keywords

Health Sciences, Rehabilitation and Therapy|Health Sciences, Recreation|Biophysics, General

Degree

Ph.D.

Abstract

Stepping typically occurs on a background of rhythmical activity. Ongoing adjustments of posture associated with rhythmic stepping under time-critical situations have not been studied. Older adults are known to have prolonged postural adjustments for voluntary stepping and changes in protective step characteristics in response to mechanical perturbations. The purpose of this study was twofold: (1) Determine if age-related differences exist in self-selected preferred rhythmic stepping performance among younger, middle-aged, and older adults. (2) Assess the influence of temporal constraints during stepping in place on postural and focal limb movement control in younger, middle-aged, and older adults. ^ Thirty-two healthy adult subjects (10 younger, 10 middle-aged, 12 older) performed rhythmic unipedal stepping at their preferred pace before and after six trials of metronome-paced stepping. Metronome-paced stepping was conducted at the following frequencies intervals: 1.0 Hz, 1.6 Hz, 2.2 Hz, 2.8 Hz, 2.2 Hz, 1.6 Hz, 1.0 Hz. Kinetic and kinematic analyses were conducted to determine body center of mass motion, step characteristics, and loading beneath the lower limbs. ^ Older subjects had longer stride periods than younger subjects in pre-pacing preferred stepping trials. Older subjects exhibited a 25% decrease in preferred stride period between pre- and post-pacing trials. This is compared to a 15% and 11 % decrease exhibited by middle-aged and younger subjects respectively. After pacing, older adults had comparable stride periods to younger subjects. Modification of the stride period occurred mainly during the stance phase of rhythmic stepping. ^ Under temporally-constrained conditions, amplitude of postural motion was suppressed with increasing pacing frequency and re-recruited (but to a lesser extent) with decreasing pacing frequency. Step length was relatively resistant to changes in pacing frequency. Older adults exhibited reductions in postural and step motion compared to younger subjects, a more pronounced hysteresis-like effect, greater postural and step variability, and step deviation. ^ Ongoing adjustments of posture serve to maintain the task goal of temporally-constrained stepping and older adults adapt both posture and step components to maintain paced rhythmic stepping. Both postural- (self-generated) and step- (protective) related adaptive strategies are needed by older adults for stepping in time-critical situations. ^