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Background. Intra-individual gait variability predicts falls and disability in older people. Knowledge of factors that contribute to gait variability may lead to interventions aimed at reducing decline in mobility and falls risk. The aim of this population-based study was to examine whether poorer performance on a range of sensorimotor measures was associated with greater gait variability. Methods. Individuals aged 60-86 years (n = 412) were randomly selected from the Southern Tasmanian electoral roll. Spatial (step length and step width) and temporal (step time and double support time [DST]) gait measures were recorded with a GAITRite walkway. Variability for each gait measure was the standard deviation of measurements recorded during six walks. Sensorimotor measures included visual contrast sensitivity, lower limb proprioception, quadriceps strength, reaction time, and body sway (eyes open and closed). Regression analysis was used to determine the relationships between sensorimotor measures and gait variability. Results. Greater sway on a foam mat (eyes closed) was associated with greater variability in all gait measures (p < .05). Slower reaction time was associated with greater variability in both temporal gait measures (p < .05), whereas poorer proprioception was only associated with greater DST variability (p = .01) and weaker quadriceps strength with greater step time variability. Other sensorimotor factors were not independently associated with gait variability. Conclusions. Body sway, reaction time, quadriceps strength, and proprioception are likely factors that may explain gait variability in the general older population. Further research is warranted to determine causality of these associations and whether intervention programs addressing these factors may reduce gait variability in older people. Key Words: Gait variability--Sensorimotor--Older adults--Population based. doi: 10.1093/gerona/glp184

Background. The purpose of this study was to explore the relationship between muscle power output at different external resistances and performance of functional tasks. The authors hypothesized that power at 40% skeletal muscle 1 repetition maximum (1RM), in which contraction velocity is high, would explain more of the variability in tasks such as level walking than would peak power or IRM strength, in which contraction velocity is lower. Methods. Participants were men and women (n = 48; ages 65-91 years) with physical disability as evidenced by 2 or more deficits on the Medical Outcomes Study Short Form physical function subscale or a score of 9 or less on the Established Populations for the Epidemiologic Studies of the Elderly short physical performance battery. Muscle strength (1RM) was measured using a bilateral leg press exercise, and power output was determined by selecting the highest power output from 6 different contraction velocities: 40%, 50%, 60%, 70%, 80%, and 90% IRM. Functional performance tasks consisted of habitual gait velocity (HGV) and stair climb (SC) and chair rise (CR) performance. Separate linear regression models were fit for each of the 3 dependent variables (SC, CR, HGV) using 1RM strength, power at 70% 1RM, and power at 40% 1RM as independent variables. All models were adjusted for age, body mass, and sex. Results. Lower extremity power at 70% and 40% 1RM demonstrated greater associations with SC and HGV than did I RM strength, whereas power at 40% I RM demonstrated similar or stronger associations with all functional tasks compared with 1RM strength. Power at 40% IRM explained the same or more of the variability in SC (R2 = .42 [regression coefficient = -.169 [+ or -].06] vs .43 [-.206 [+ or -].071]), CR ([R.sup.2] = .28 [-.154 [+ or -].057] vs .24 [-.152 + .070]) and HGV ([R.sup.2] = .59 [.214 + .37] vs .51 [.223 [+ or -].049]) compared with power at 70% 1RM. Power at 40% 1RM explained more of the variability in the lower intensity (HGV) compared with the higher intensity (SC or CR) functions. Conclusions. Power output at 40% of IRM explained more of the variability in HGV than did power at 70% 1RM, suggesting that measures such as HGV that require a lower percentage of maximal strength to perform might be more sensitive to differences in contraction velocity. Because HGV is highly predictive of subsequent disability, future studies should evaluate the determinants of muscle power output at low external resistances.