Jump-Land Characteristics and Muscle Strength Development in Young Athletes

Abstract

Background Many authors have speculated that altered neuromuscular control and strength of the lower extremity are responsible for the gender disparity in knee ligament injury rates. Hypothesis Significant increases in normalized quadriceps and hamstrings strength and limb symmetry on single-legged hop test occur with age. No gender differences in strength occur until age 14 years, after which boys generate greater peak torques than do girls. Age and gender do not influence lower limb alignment on a drop-jump test. Study Design Cross-sectional study; Level of evidence, 3. Methods We studied the effects of age and gender in 1140 athletes, 9 to 17 years old, on muscle strength and neuromuscular control during functional activities. Isokinetic quadriceps and hamstrings strength was measured at 300 deg/s. Limb symmetry was assessed with single-legged hop tests. A video drop-jump test determined lower limb alignment in the coronal plane. Results Extension peak torques significantly increased with age; maximum strength was noted in girls at age 13 years and in boys at age 14 years (P< .001). Although maximum flexion strength occurred in boys at age 14 years (P< .001), girls had only slight increases from ages 9 to 11 years (P= not significant). Boys aged 14 to 17 years had significantly greater normalized isokinetic strength than did age-matched girls. No age or gender effects existed in limb alignment on the drop-jump test or limb symmetry on single-legged hop testing. Conclusion Maximum hamstrings strength was noted in female athletes by age 11 years, compared with age 14 years in male athletes, and a distinct lower limb valgus alignment existed in the majority of all athletes on landing. The absence of a gender difference in lower limb alignment on landing suggests other factors may be responsible for the gender disparity in knee ligament injury rates.