Associations Between Measures of Physical Activity and Muscle Size and Strength: A Systematic Review.
Zachary P Rostron, Rodney A Green, Michael Kingsley and 1 others
PMID 34179760WHAT IT FOUND
Objective physical activity measures like accelerometers showed moderate positive associations with lower limb muscle size and strength.
Self-reported activity showed negative associations in older adults. Use device-based data rather than questionnaires when predicting muscle outcomes.
Key findings
01Objective measures of physical activity had a moderate positive correlation with lower limb muscle size (r = 0.30).
02Subjective measures of physical activity had a strong negative correlation with muscle size across all ages (r = -0.59).
03Lower limb muscle strength and muscle size showed a moderate positive correlation (r = 0.26).
STILL TO COME
How it was doneWhat they foundWhat it means for PTsWhat it means for OTs
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What it does not show
The analysis relied on converting data to z scores using normative values, which involved many calculations and assumptions about typical sex differences. Most studies measured physical activity over only one week, which may not capture long-term habits or account for the time required for muscle changes to occur. Individual body size data were not available for all participants, so strength and muscle size could not be normalized to body weight, a key factor in muscle performance. The review included a mix of healthy adults and those with various pathologies, which may influence the generalizability of the correlations to specific clinical populations.
Declared interests
The provided text does not contain a specific funding or conflict of interest declaration.
The easy way to misread this
Do not interpret the negative correlation between self-reported physical activity and muscle outcomes as evidence that activity harms muscle size or strength. This finding likely reflects inaccuracies in how older or overweight individuals estimate their activity levels on questionnaires, rather than a true physiological effect.