Developmental Changes in Isometric Strength: Longitudinal Study in Adolescent Soccer Players

摘要

This study aimed to examine longitudinal changes in isometric strength of the knee extensors (ImKE) and knee flexors (ImKF) at 30 degrees and 60 degrees. The sample was composed of 67 players aged 11.0-13.9 years at baseline over five years. Stature, body mass, skinfolds, and isometric strength (ImKE30 degrees, ImKF30 degrees, ImKE60 degrees and ImKF60 degrees) were measured. Fat mass and fat-free mass (FFM) were derived from skinfolds. Skeletal age was obtained using TW2 RUS. Multilevel random effects regression analyses extracted developmental polynomial models. An annual increment on chronological age (CA) corresponded to 5.6 N (ImKE30 degrees), 2.7 N (ImKF30 degrees), 4.6 N (ImKE60 degrees) and 1.5N (ImKF60 degrees). An increment of 1 kg in FFM predicted isometric strength as follows: 1.2 N (ImKE30 degrees), 2.1 N (ImKF30 degrees), 3.1 N (ImKE60 degrees) and 2.0 N (ImKF60 degrees). The following equations were obtained: ImKE30 degrees = 5.759 x CA + 1.163 x FFM; ImKF30 degrees= -19.369 + 2.691 x CA + 0.693 x CA(2) + 2.108 x FFM; ImKE60 degrees = 4.5 53 x CA + 3.134 x FFM; and, ImKF60 degrees= -19.669 + 1.544 x CA + 2.033 x FFM. Although skeletal maturity had a negligible effect on dependent variables, age and body size, based on FFM, were relevant longitudinal predictors. During adolescence, systematic assessment of knee extensors and knee flexors are strongly recommended to prevent impairment of knee muscle groups.