Grip strength and hand dominance: challenging the 10% rule.

The purpose of this study was to test the utility of the 10% rule in hand rehabilitation. The 10% rule states that the dominant hand possesses a 10% greater grip strength than the nondominant hand. This rule has been used for many years to assist therapists in setting strength goals for patients with injured hands. The sample for this study consisted of 310 male and female students, faculty, and staff from a small, private liberal arts college located in Pennsylvania. Grip strength was measured with a factory-calibrated Jamar dynamometer. Results showed an overall 10.74% grip strength difference between dominant and nondominant hands. This finding verified the 10% rule. However, when the data were separated into left-handed and right-handed subjects, a 12.72% difference for right-handed subjects and a -0.08% difference for left-handed subjects was found. In conclusion, this study showed that the 10% rule is valid for right-handed persons only; for left-handed persons, grip strength should be considered equivalent in both hands.