Hand strength and prone extension in right-dominant, 6 to 9 year olds.

A stratified random sample of 153 right-dominant children (6 to 9 years of age) with normal or above intelligence was selected to study the development of hand strength, and the quality and duration of prone extension as a function of age, sex, height, and weight of the child. The Jamar hand dynamometer was used to measure hand strength, and a new scale for rating the quality of prone extension was presented. Both right- and left-hand strength increased monotonically with age, with the right being significantly higher than the left. Duration of prone extension increased monotonically with age, but quality of prone extension did not correlate with age. Sex differences were found only on the variable left-hand strength (males greater than females). Hand strength demonstrated weak correlation with duration of prone extension. Both height and weight exhibited strong positive correlations with hand strength, weaker positive correlations with duration of prone extension, and no correlation with quality of prone extension. The results suggest hand strength can be an index of normal development, and children ages 6 to 9 can attain the prone extension position; however, the meaning of duration greater than 30 seconds needs to be researched further.