A normative sample of isotonic and isokinetic muscle strength measurements in children 7 to 12 years of age

Aim: To provide normative age- and gender-associated values on muscular strength, power and endurance and to establish a reference database on healthy school children aged 7 to 12 years. In addition, associations between some simple functional tests and the more sophisticated isokinetic strength measures were investigated. Methods: Three hundred seventy-six children, 191 girls and 185 boys, performed different muscle-strength tests like knee flexion/extension, handgrip, back extension and vertical jump. Results: There was a significant and linear increase in strength with no gender differences from 7 up to 11 years of age. There was a large variability within each age group, indicating that a normative sample of muscle-strength measurements includes a wide range of values for each age group. The relationship between hand- grip strength and observed quadriceps strength was high (r = 0.84) and the correlation between vertical jump and relative quadriceps strength was moderate (r = 0.50). Conclusion: All the different strength measures showed almost the same pattern, indicating increased absolute strength values with increasing age and no significant gender differences except for flexion at the age of 11 and 12 years . The association between grip strength, vertical jump and quadriceps strength measured isokinetically was moderate to strong. The back muscle endurance test (The Biering-Sorensen test) showed a great roof effect and should not be included in a test battery for school children.