Does The Weaker Limb Limit Physical Performance In Older Adults?

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PURPOSE: The purpose of this study was to examine the relationship of unilateral knee extensor strength asymmetry to physical function in adults at risk of mobility-limitation. METHODS: 30 subjects (75.2±6.9 yr, 167.5±9.0 cm, 74.7±14.0 kg) had their maximal voluntary isometric knee extension strength measured on a dynamometer for each limb. Subject’s percent asymmetry between the strong limb (SL) and weak limb (WL) was calculated. Those with asymmetries >10% were placed in the asymmetrical group (AG, n=14) and those <10% were placed in the symmetrical group (SG, n=16). Physical function was assessed during a timed 400m walk, chair-rise, and stair ascent. It was hypothesized that AG would have a lower level of function that was limited by the weak limb. A multivariate analysis of variance was used to examine differences in strength and performance between groups. Pearson correlations were used to study the relationship between leg strength and physical function. Significance was p<0.05. RESULTS: AG had greater strength asymmetry (22.6±15.8%) than SG (4.3±3.3%, p<0.01), lower WL strength (1.15±0.36 Nm kg-1 vs 1.55±0.43 Nm kg-1, p=0.01), but similar SL strength (1.48±0.30 Nm kg-1 vs 1.63±0.43 Nm kg-1, p=0.30). WL strength was correlated with SL strength (r = 0.90, p<0.01), 400m walk (r = -0.41, p<0.01), chair-rise (r = -0.39, p=0.01), and stair ascent (r = -0.36, p=0.01). SL strength was similarly correlated with 400m walk (r = -0.50, p<0.01), chair-rise (r = -0.40, p=0.01), and stair ascent (r = -0.42, p<0.01). There was no difference in physical function between groups (p>0.05) nor were there correlations between degree of asymmetry and physical function (p>0.05). CONCLUSION: Strength asymmetry did not limit physical function in this sample of older adults because the relative strength of each limb was more closely related to performance than the difference in strength between them, and, within an individual WL and SL strength were highly correlated. Leg strength criteria are often used to evaluate the risk of falls and mobility loss in older adults and it is currently not clear how strength asymmetry affects these relationships. Supported by: NIH Grant 1R15 A6040700-01A1