Has Muscle Power Better Discriminative Capacity Compared to Muscle Strength in Predicting Worsening Disability in Older Adults?

BACKGROUND: Poor muscle strength is a risk factor for disability; nonetheless, its discriminative capacity in identifying people who will become disabled is poor. We evaluated whether muscle power, which also is a risk factor for disability, has better discriminative capacity compared to muscle strength.METHODS: We used data from the population-based InCHIANTI study. Our outcome measure was the loss of at least 1 basic or instrumental activity of daily living between baseline and 3-year follow-up visit. Body weight standardized knee isometric strength and leg power (power rig) were used as exposure variables. Discriminative capacity was estimated using the area under the receiver-operating curves. Both strength and power were dichotomized as below versus equal of above sex-specific first quartile. Sensitivity, specificity, and positive/negative predictive values (PPV, NPV) were calculated.RESULTS: We included 763 participants (415 women), with a mean age of 73.5 years (standard deviation: 6.4). In men, using muscle strength we obtained an area under the curve (AUC) of 0.70, with sensitivity = 0.45, specificity = 0.80, PPV = 0.27, and NPV = 0.90; using muscle power we obtained an AUC of 0.82, sensitivity = 0.73, specificity = 0.86, PPV = 0.46, and NPV = 0.95. In women, using muscle strength we obtained an AUC of 0.62, with sensitivity = 0.39, specificity = 0.81, PPV = 0.39, and NPV = 0.81; using muscle power we obtained an AUC = 0.69, sensitivity = 0.40, specificity = 0.83, PPV = 0.42, and NPV = 0.82.CONCLUSIONS: We found that in men muscle power had better discriminative capacity, especially higher sensitivity, compared to muscle strength for prediction of worsening disability. No meaningful difference in overall discriminative capacity was found in women.