Strength And Power As Indicators Of Differences In Fiber Type Contributions In Children And Adolescents

Abstract

PURPOSE: Examine individual patterns of peak torque (PT) and mean power (MP) across a range of angular velocities in children and adolescents and how these patterns relate to measurements of growth. METHODS: Seventeen children (age = 11 ± 0.4 years) and 22 adolescents (age = 14 ± 0.6 years) performed maximal voluntary isometric contractions, isokinetic leg extensions at 60, 120, 180, 240, and 300°·s-1, and 50 consecutive maximal isokinetic leg extensions at 180°·s-1. Patterns of responses for PT and MP across angular velocity were fit with quadratic equations for each subject with r2 values ranging from 0.803-0.934 for PT and 0.908-0.996 for MP, respectively. Derivatives of each quadratic formula quantified velocity-related changes in PT and MP. Each quadratic formula predicted the peak velocity at which torque could be generated (VPT) or the velocity at which the greatest MP would occur (VMP). The percent of fast-twitch fibers (FT%) was estimated from the fatigue index of the 50-repetition test. Measurements of growth included age, maturity offset, height, body mass, fat-free mass, and quadriceps femoris muscle cross-sectional area. RESULTS: All measurements of growth, PT, and MP were greater for adolescents than children (p ≤ 0.003). As expected, PT decreased quadratically (p < 0.001), while MP increased quadratically to 180-240°·s-1 (p < 0.001) and plateaued (p = 0.056) or decreased (p < 0.001) to 300°·s-1. VPT was 352 ± 18 Nm for children and 527 ± 34 Nm for adolescents (p < 0.001), while VMP was 216 ± 11 W for children and 268 ± 11 W for adolescents (p < 0.001). FT% was 39 ± 4% for children and 46 ± 4% for adolescents (p < 0.001). Derivatives indicated that PT decreased while MP increased across velocity more rapidly in adolescents than children (p ≤ 0.016). Derivatives of PT vs. velocity exhibited a high relationship with body mass for adolescents (r = -0.727), while derivatives of MP vs. velocity exhibited high relationships with body mass and fat-free mass in children (r = 0.714-0.795). VTQ and VMP exhibited high relationships with age for adolescents (r = 0.884). CONCLUSION: Isometric and isokinetic muscle actions in children and adolescents indirectly demonstrate between growth-related increases in fast-twitch fiber contributions to maximal, voluntary muscle strength and power across the velocity spectrum.