title: Proprioceptive acuity predicts muscle co-contraction of the tibialis anterior and gastrocnemius medialis in older adults' dynamic postural control.
abstract: Older adults use a different muscle strategy to cope with postural instability, in which they 'co-contract' the muscles around the ankle joint. It has been suggested that this is a compensatory response to age-related proprioceptive decline however this view has never been assessed directly. The current study investigated the association between proprioceptive acuity and muscle co-contraction in older adults. We compared muscle activity, by recording surface electromyography (EMG) from the bilateral tibialis anterior (TA) and gastrocnemius medialis (GM) muscles, in young (aged 18-34) and older adults (aged 65-82) during postural assessment on a fixed and sway-referenced surface at age-equivalent levels of sway. We performed correlations between muscle activity and proprioceptive acuity, which was assessed using an active contralateral matching task. Despite successfully inducing similar levels of sway in the two age groups, older adults still showed higher muscle co-contraction. A stepwise regression analysis showed that proprioceptive acuity measured using variable error was the best predictor of muscle co-contraction in older adults. However, despite suggestions from previous research, proprioceptive error and muscle co-contraction were negatively correlated in older adults, suggesting that better proprioceptive acuity predicts more co-contraction. Overall, these results suggest that although muscle co-contraction may be an age-specific strategy used by older adults, it is not to compensate for age-related proprioceptive deficits.
authors.affiliation: Department of Psychology, Queen's University Belfast, Belfast BT, UK. Electronic address: ccraig25@qub.ac.uk.
authors.forename: C E
authors.initials: CE
authors.lastname: Craig
authors.affiliation: School of Exercise & Nutritional Sciences, San Diego State University, San Diego 92101, USA. Electronic address: dgoble@mail.sdsu.edu.
authors.forename: D J
authors.initials: DJ
authors.lastname: Goble
authors.affiliation: Department of Psychology, Queen's University Belfast, Belfast BT, UK. Electronic address: m.doumas@qub.ac.uk.
authors.forename: M
authors.initials: M
authors.lastname: Doumas
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D004576:Electromyography; D005260:Female; D006801:Humans; D007866:Leg / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D004856:Postural Balance / Q000502:physiology*; D011187:Posture / Q000502:physiology; D011434:Proprioception / Q000502:physiology*; D012044:Regression Analysis; D055815:Young Adult
keywords: EMG; aging; muscular coactivation; posture; proprioception