Rate of Force Development as a Predictor of Mobility in Community-dwelling Older Adults
Garrett M. HesterPhuong L. HaBenjamin E. DaltonTrisha A. VanDusseldorpAlex A. OlmosMatthew T. StrattonAlyssa R. BaillyTara M. Vroman
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Background and Purpose: Rate of force development (RFD) is influential, and possibly more influential than other muscular performance parameters, for mobility in older adults. However, only a few studies have investigated this matter, and this has not been examined for the plantar flexors (PFs). The purpose of this study was to examine the contribution of PF RFD and other common tests of muscular performance to Up-and-Go (UG) performance and walking speed (WS) in older adults. Methods: Twenty-six (19 females) healthy, community-dwelling older adults (73.7 ± 4.9 years) were recruited from a senior citizen center for this observational study. Handgrip strength, UG performance, as well as preferred and maximal WS were obtained. Time taken to complete 5-chair rises and the number of chair rises completed in 30 seconds were recorded. Rate of force development of the PFs was obtained during a rapid, bilateral calf raise performed on a force plate. Hierarchical multiple linear regression was used to identify significant predictors, after adjusting for physical activity level and body mass index, of mobility (ie, UG, preferred and maximal WS). Results and Discussion: No muscular performance variables correlated with preferred WS. Rate of force development (adjusted R 2 = 0.356; P = .008) and handgrip strength (adjusted R 2 = 0.293; P = .026) were the only predictors of maximal WS and accounted for a 21.7% and 16.1% change in R 2 , respectively, after accounting for physical activity level and body mass index. Rate of force development was the only predictor of UG performance (adjusted R 2 = 0.212; P = .006) and accounted for a 29.2% change in R 2 after adjustment variables were applied. Conclusions: Compared to common assessments of muscular performance, such as handgrip strength and chair rise performance, PF RFD was a greater predictor of mobility in older adults. These findings, in conjunction with recent reports, indicate that the assessment of RFD likely complements strength testing, thereby enabling a more robust assessment of functional decline in older adults.Many questions in human health research can only be answered with observational studies. In contrast to controlled experiments or well-planned, experimental randomized clinical trials, observational studies are subject to a number of potential problems that may bias their results.Some of the more important problems affecting observational studies are described and illustrated by examples. Additional information is provided with reference to a selection of the literature.Factors that may bias the results of observational studies can be broadly categorized as: selection bias resulting from the way study subjects are recruited or from differing rates of study participation depending on the subjects' cultural background, age, or socioeconomic status, information bias, measurement error, confounders, and further factors.Observational studies make an important contribution to medical knowledge. The main methodological problems can be avoided by careful study planning. An understanding of the potential pitfalls is important in order to critically assess relevant publications.
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