Abstract
BackgroundApproximately 35% of individuals > 70 years have mobility limitations. Historically, it was posited lean mass and muscle strength were major contributors to mobility limitations, but recent findings indicate lean mass and muscle strength only moderately explain mobility limitations. One likely reason is that lean mass and muscle strength do not necessarily incorporate measures globally reflective of motor function (defined as the ability to learn, or to demonstrate, the skillful and efficient assumption, maintenance, modification, and control of voluntary postures and movement patterns). In this study we determined the relative contribution of lean mass, muscle strength, and the four square step test, as an index of lower extremity motor function, in explaining between-participant variance in mobility tasks.MethodsIn community-dwelling older adults (N = 89; 67% women; mean 74.9 ± 6.7 years), we quantified grip and leg extension strength, total and regional lean mass, and time to complete the four square step test. Mobility was assessed via 6-min walk gait speed, stair climb power, 5x-chair rise time, and time to complete a complex functional task. Multifactorial linear regression modeling was used to determine the relative contribution (via semi-partial r2) for indices of lean mass, indices of muscle strength, and the four square step test.ResultsWhen aggregated by sex, the four square step test explained 17–34% of the variance for all mobility tasks (p < 0.01). Muscle strength explained ~ 12% and ~ 7% of the variance in 6-min walk gait speed and 5x-chair rise time, respectively (p < 0.02). Lean mass explained 32% and ~ 4% of the variance in stair climb power and complex functional task time, respectively (p < 0.02). When disaggregated by sex, lean mass was a stronger predictor of mobility in men.ConclusionThe four square step test is uniquely associated with multiple measures of mobility in older adults, suggesting lower extremity motor function is an important factor for mobility performance.Trial registrationNCT02505529–2015/07/22.
Highlights
35% of individuals > 70 years have mobility limitations
The overall R2 values explained by the four square step test, muscle strength, and lean mass, for 6-min walk gait speed, stair climb power, 5x chair rise time, and the time to complete the complex function task, were 0.66, 0.66, 0.50, and 0.53, respectively (p < 0.01)
The variance inflation factor (VIF) values for each predictor variable are acceptable with all values under 2.2
Summary
35% of individuals > 70 years have mobility limitations. Historically, it was posited lean mass and muscle strength were major contributors to mobility limitations, but recent findings indicate lean mass and muscle strength only moderately explain mobility limitations. One likely reason is that lean mass and muscle strength do not necessarily incorporate measures globally reflective of motor function (defined as the ability to learn, or to demonstrate, the skillful and efficient assumption, maintenance, modification, and control of voluntary postures and movement patterns). Previous research in older adults has focused largely on musculoskeletal mechanisms and processes underlying mobility limitations. This focus is likely due to the premise that sarcopenia, the age-related loss of lean mass [11], results in reduced muscle strength, which is a major contributor to mobility limitations in older adults [12]. We assert that motor function is an important contributor to age-related mobility limitations above and beyond the associations found with lean mass and muscle strength
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