THE RELATIONSHIP BETWEEN LOWER LIMB STIFFNESS AND RUNNING ECONOMY IN CHILD SOCCER PLAYERS

Introduction: Lower limb stiffness has been shown to be associated with running economy (RE) in adults, but this relationship in children remains unclear. Objectives: The purpose of this study was to investigate the relationship between lower limb stiffness, RE, and repeated-sprint ability in child soccer players. Methods: Twenty-eight male child soccer players (mean age 11.8 +/- 0.9 years) participated in the study. RE was determined by measuring the steady-state oxygen uptake (ml/min/kg) at submaximal running speeds of 8 and 9 km/h. Vertical and leg stiffness were calculated from the flight and contact time data obtained during two submaximal running tests. Additionally, vertical stiffness was measured during the maximal and submaximal hopping tests. All participants performed the repeated sprint test consisting of 10 x 20-m all-out sprints interspersed with 20-s active recovery. Results: During both su bmaxima I running tests, vertical (r= -0.505 to -0.472) and leg stiffness (r= -0.484 to -0.459) were significantly correlated with RE (p< 0.05). Maximal (r= -0.450) and submaximal hopping stiffness (r= -0.404) were significantly correlated with RE at 8 km/h (p< 0.05). Maximal hopping stiffness was significantly correlated with the best sprint time (r= -0.439) and mean sprint time (r= -0.496) (p< 0.05). Vertical (r= -0.592 to -0.433) and leg stiffness (r= -0.612 to -0.429) at 8 and 9 km/h and submaximal hopping stiffness (r= -0.394) were significantly correlated with the fatigue index (p< 0.05). Conclusions: Current findings indicate that the lower limb stiffness may be an important determinant of both RE and repeated-sprint ability in child soccer players.