A comprehensive scoping review and meta-analysis of upper limb strength asymmetry.

The "10% rule" of handedness asserts the dominant hand is 10% stronger than the non-dominant hand. Primarily derived from handgrip data, it is unclear if a generalized asymmetry exists across the upper limb. Understanding how strength asymmetry may be affected by handedness, sex, and exertion type has important implications for ergonomics design, sports performance, and clinical rehabilitation. The purpose of this study was to systematically synthesize currently available evidence examining upper limb strength asymmetry. 10,061 results were retrieved, and 174 studies remained after title/abstract screening. 87 studies were synthesized. Results are compiled by exertion type and manner of asymmetry comparison (i.e. right/left, dominant/non-dominant). Asymmetry ratios were calculated to examine the effects of handedness, exertion side, arm region, and sex. Strength differences were most frequently reported for grip exertions (n = 49). 25 studies reported other joint strength asymmetries. Overall, the right limb was 6.7% stronger than the left limb (n = 9342) and the dominant limb was 11.6% stronger than the non-dominant limb (n = 9327), though strength asymmetry varied across joints and movements (2.1% to 19.5%). This research demonstrates that the 10% rule is a good approximation for upper limb strength asymmetry. However, several factors, including joint, movement type, and sex, can affect this relationship.