Isometric strength of upper limb muscles in youth using hand-held and hand-grip dynamometry.

The present study aimed to determine the isometric strength profile of the upper limb muscles of children and adolescents between 7-15 years of age. Furthermore, to (a) identify the age at which differences in strength are observed between sexes; to (b) determine the age range at which significant progression of strength could be observed; and (c) identify the role of each muscle on the total upper limb strength. Cross-sectional study that evaluated the isometric strength of nine muscle groups of the upper limb of 243 Chilean children, split into 9 age groups, separated by 1-year intervals. For this, hand-held dynamometry and hand-grip dynamometry were used. A two-factor analysis of variance for the maximum isometric strength and a stepwise multiple linear regression analysis were performed. From 11 years of age, wrist flexors were the first muscle group that revealed a significant difference in isometric strength in favor of boys ( P =0.0143). In boys, the narrowest and earliest age range in the progression of isometric strength was 10 to 12 years for wrist flexors ( P =0.0392). Shoulder flexors was the main factor that explained the performance of the total upper limb strength ( R 2 =0.742; P <0.001). The most progressive isometric strength development occurred from age 10 years in the ventral and distal muscles of the upper limb; and from this age the boys begin to present a greater isometric strength than girls. In addition, the isometric strength of shoulder flexors explained the higher total upper limb strength performance.