Peak Torque Explains More Unique Variability in Growth Measurements than Rate of Torque Development in Young Boys and Girls

This study reported test-retest reliability and evaluated collinearity for isometric leg extension and flexion peak torque (PT) and rate of torque development (RTD) in young boys and girls. Measurements of growth included height, body mass, fat-free mass, maturity offset, and leg extensor and flexor muscle cross-sectional area. Maximal isometric contractions quantified PT and RTD. Intraclass correlation coefficients (ICCs), SEM, coefficients of variation, and minimum detectable changes quantified test-retest reliability. Zero-order correlations and first-order partial correlations evaluated collinearity. Peak torque from leg extension and flexion exhibited ICCs ≥ 0.90, RTD from leg extension and flexion exhibited ICCs ≥ 0.38. Partialing out leg flexion PT reduced the relationships between leg extension PT and growth (r_{PText, growth.PTflex}= 0.392-0.605). Partialing out leg extension PT eliminated the relationships between leg flexion PT and growth (r_{PTflex, growth.PText}= 0.098-0.263). Partialing out leg extension RTD reduced the relationships between PT and growth (r_{PText, growth.RTDext}= 0.516-0.775). Partialing out leg extension PT eliminated the relationships between RTD and growth (|r_{RTDext, growth.PText}| = 0.001-0.148). Leg extension PT was more reliable and explained the most unique variability in growth among young boys and girls. In contrast, RTD was less reliable and was fully accounted for by PT, indicating that RTD may be an unnecessary measurement in studies of young boys and girls.