Does skeletal muscle morphology or functional performance better explain variance in fast gait speed in older adults?

BACKGROUND: Fast gait speed is being increasingly recognized as an important clinical tool in older adults. However, the underlying muscular and functional contributors to fast gait speed performance remain poorly understood. AIM: We sought to determine predictors of fast gait speed in older adults. We hypothesized that lower-extremity skeletal muscle size and quality would be strong predictors. METHODS: Ninety community-dwelling older adults (33 men, 57 women; mean ± SD age = 74 ± 6 years) participated. B-mode ultrasonography was used to capture images of the vastus lateralis, rectus femoris, and gastrocnemius in the transverse plane. Each participant performed 30-second chair stand, heel-rise, functional reach, and grip strength tests. Fast gait speed was measured using the NIH Toolbox 4-Meter Walk Test. ImageJ software was used to quantify cross-sectional area (CSA), subcutaneous tissue thickness, and echo intensity. Two separate stepwise regression analyses were performed, one using muscle morphology variables as independent variables, and another including the functional outcomes. RESULTS: The ultrasound variables exhibited weak-to-moderate correlations with fast gait speed (|r| range = 0.168-0.416). The initial regression analysis indicated that the combination of medial gastrocnemius CSA and subcutaneous tissue thickness explained 22.8% of the variance in fast gait speed. The secondary analysis indicated that 30-second chair stand, heel-rise, and grip strength performance explained 45.5% of the variance. CONCLUSION: While medial gastrocnemius morphology is important, measures of upper and lower-extremity muscle function are better predictors of fast gait speed. These results highlight a dissociation between skeletal muscle morphology and fast gait speed.

Validity and reliability of the NIH Toolbox® Standing Balance Test As compared to the Biodex Balance System SD.

BACKGROUND/ PURPOSE: The NIH Toolbox® was developed to assess functions among motor, sensory, emotional, and cognitive domains. The motor domain of the NIH Toolbox® includes an assessment for standing balance. Studies have validated early versions of the balance assessment for ages 3 through 85; however, no studies have examined the reliability and validity in its current version (using iPod Touch) against established balance measurements such as the Biodex SD modified clinical test of sensory integration of balance (m-CTSIB). SUBJECTS: Ninety-three community dwelling older adults (38 males 55 females) ≥60 years old (SD 74 ± 6). METHODS: One-day assessment using the NIH Toolbox® and the Biodex SD m-CTSIB. Intraclass correlation coefficients (ICC3,1) were used to measure the test-retest reliability, and Pearson's product correlation examined criterion validity. RESULTS: The overall composite of the Biodex SD m-CTSIB and NIH Toolbox® showed moderate test-retest reliability (ICC3,1 = 0.71, MDC = 1.21) (ICC3,1 = 0.84, MDC = 0.65,) respectively. The NIH Toolbox® Theta Score and Biodex overall Sway Index (SI) shows acceptable reliability criterion validity (r = 0.52) indicating moderate overlap in constructs. CONCLUSIONS: The NIH Toolbox®balance assessment demonstrates acceptable criterion validity compared to the Biodex SD m-CTSIB. The NIH Toolbox® is a valid, reliable, and accessible device; therefore, the NIH Toolbox® should be considered for use in clinical evaluations.