Reliability of quantitative strength measurements in children.

In normal children, sex, age, height and weight account for approximately 50% to 70% of variance in the strength scores obtained by quantitative measurements. Although quantitative techniques accurately measure the forces generated by muscle contraction, technical and psychological variables may cause some inconsistency of scores and contribute to the variance observed. To explore the role of these factors, reliability of quantitative strength measurements was examined in children withe normal intelligence and with mild mental retardation using the isokinetic method. Results showed mean score deviations of 5.3% to 5.8% for different muscle groups within the same test. When testing was repeated by the same examiners 7 to 10 days apart, mean score deviations were 7.9% to 9.8% in various muscle groups. Repeated measurements by different examiners 7 to 10 days later yielded 8.7% to 10% mean score deviations for various muscles. Statistical analyses showed that these differences were not significant. Technical and behavioral aspects of test performance are not an important source of inaccuracy and, therefore, cannot contribute significantly to the variance of scores.