What is a Clinically Meaningful Improvement in Leg-Extensor Power for Mobility-limited Older Adults?

Muscle power is a key predictor of physical function in older adults; however, clinically meaningful improvements in leg-extensor muscle power have yet to be identified. The purpose of this study is to establish the minimal clinically important improvement (MCII) and substantial improvement (SI) for leg-extensor power and muscle contraction velocity in mobility-limited older adults.

Data were extracted from three randomized trials of leg-extensor muscle power training interventions (3- to 6-month duration). Measurements of leg-extensor power and velocity were obtained using dynamic bilateral leg press at 40% and 70% of the one-repetition maximum. Anchor-based MCIIs were calculated using selected items extracted from the Late Life Function and Disability Instrument. Standard error of measurement and effect size methods were used to calculate the distribution-based MCII.

Data from 164 participants (mean age: 76.6 ± 5.6 years; Short Physical Performance Battery score: 7.8 ± 1.3) were used in this analysis. The respective MCII and SI estimates for 40% leg-extensor power were 18.3 (9%) and 30.5 (15%) W, and 23.1 (10%) and 41.6 (18%) W for 70% leg-extensor power. The respective MCII and SI estimates for 40% average velocity were 0.03(7%) and 0.08(18%) m/s, and 0.02(6%) and 0.05(15%) m/s for 70% average velocity.

This is the first study to establish a clinically meaningful improvement of leg-extensor power (9%-10%) and velocity (6%-7%) in mobility-limited older adults. These findings should be used to aid in the design and interpretation of clinical trials and interventions that target improvements in muscle power in this high-risk population.