Are changes in leg power responsible for clinically meaningful improvements in mobility in older adults?

Abstract

Objectives: From among physiological attributes commonly targeted in rehabilitation, to identify those in which changes led to clinically meaningful differences (CMDs) in mobility outcomes.

Design: Secondary analysis of data collected for a randomized controlled trial of exercise using binary outcomes defined by recording a large CMD (Short Physical Performance Battery (SPPB)=1 unit; gait speed (GS)=0.1 m/s). Iterative models were performed to evaluate possible confounding between physiological variables and relevant covariates.

Setting: Outpatient rehabilitation centers.

Participants: Community-dwelling mobility-limited older adults (n=116) participating in a 16-week randomized controlled trial of two modes of exercise.

Measurements: Physiological measures included leg power, leg strength, balance as measured according to the Performance-Oriented Mobility Assessment (POMA), and rate pressure product at the maximal stage of an exercise tolerance test. Outcomes included GS and SPPB. Leg power and leg strength were measured using computerized pneumatic strength training equipment and recorded in Watts and Newtons, respectively.

Results: Participants were 68% female, had a mean age of 75.2, a mean of 5.5 chronic conditions, and a baseline mean SPPB score of 8.7. After controlling for age, site, group assignment, and baseline outcome values, leg power was the only attribute in which changes were significantly associated with a large CMD in SPPB (odds ratio (OR)=1.48, 95% confidence interval (CI)=1.09-2.02) and GS (OR=1.31, 95% CI=1.01-1.70).

Conclusion: Improvements in leg power, independent of strength, appear to make an important contribution to clinically meaningful improvements in SPPB and GS.

Trial registration: ClinicalTrials.gov NCT00158119.

Conflict of interest statement

Conflict of Interest: Dr. Bean was funded by Dennis W. Jahnigen Scholars Career Development Award, American Geriatrics Society/Hartford Foundation, aNIHMentored Clinical Scientist Development Award (K23AG019663-01A2) and by the department of PM&R, Harvard Medical School. The Clinical trial from which this analysis was obtained is registered (reg. # NCT00158119). Aspects of this investigation were presented at the May 2010 Annual Assembly of the American Geriatrics Society, Orlando, FL.

None of the authors have any financial interests related to this article. None have conflicts of interest, financial arrangements, or consultantships with a company whose product is associated with the submitted manuscript.

© 2010, Copyright the Authors. Journal compilation © 2010, The American Geriatrics Society.

Figures

Figure 1

Multivariate logistic models predicting clinically meaningful differences (CMD) in the SPPB among participants completing 16 weeks of training in the InVEST study (N= 117) Model 1: adjusted for age, site, treatment group Model 2: Model 1 + Δ Strength, baseline value of outcome RI: Rehabilitative Impairment CMD: Clinically Meaningful Difference SPPB: Short Physical Performance Battery ΔBalance: Change in score on the POMA balance test ΔPower: Change in Leg Power ΔPOMA: Change in Performance Oriented Mobility Assessment – Balance Score ΔRPP: Change in Rate Pressure Product (heart rate × systolic blood pressure)

Figure 2

Multivariate logistic models predicting clinically meaningful differences (CMD) in gait speed among participants completing 16 weeks of training in the InVEST study (N= 117) Model 1: adjusted for age, site, treatment group Model 2: Model 1 + Δ Strength, baseline value of outcome RI: Rehabilitative Impairment CMD: Clinically Meaningful Difference SPPB: Short Physical Performance Battery ΔBalance: Change in score on the POMA balance test ΔPower: Change in Leg Power ΔPOMA: Change in Performance Oriented Mobility Assessment– Balance Score ΔRPP: Change in Rate Pressure Product (heart rate × systolic blood pressure)