Bidirectional association between physical activity and muscular strength in older adults: Results from the UK Biobank study.

In contrast, when the imprecise measure is analysed as the outcome variable, the magnitude of effect is estimated accurately, but the standard error of the estimate is increased and the corresponding confidence intervals widened, making the result less likely to be significant. 26 Consequently, under the assumption that the associations between physical activity and grip strength are bidirectionally equivalent, as grip strength is measured with greater precision it will always appear that it is the stronger predictor of physical activity rather than vice versa.

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