Modulation of Lower Limb Biomechanics and Muscle Activation by Midsole Hardness in Children During Running.

INTRODUCTION: Children's developing musculoskeletal systems are highly sensitive to mechanical stimuli. This study investigated the effects of running shoe midsole hardness (MH) (soft midsole [SM], medium midsole [MM], and hard midsole [HM]) on lower-limb biomechanics and muscle activation during the running stance phase in children. METHODS: Thirty healthy boys participated. Kinematic, kinetic, electromyographic, and navicular height (NH) data were collected during running. Differences across the three hardness conditions were analyzed using one-way repeated-measures ANOVA. RESULTS: Maximum ankle sagittal angle decreased from 29.12° (SM) to 27.11° (HM) (p = 0.008), and hip sagittal range of motion (ROM) decreased from 43.06° (SM) to 39.66° (HM) (p = 0.047). NH was significantly higher under MM (12.48 mm) and HM (12.93 mm) than under SM (10.92 mm) (both p < 0.001). Vertical average loading rate (VALR) was significantly higher in HM (64.18 BW/s) than SM (53.14 BW/s; p = 0.032). Regarding muscle activation, significant main effects of MH were observed for the relative contributions of the tibialis anterior (TA), lateral gastrocnemius (LG), and semitendinosus (ST) (p = 0.046, p = 0.010, and p = 0.011, respectively). Post hoc comparisons showed that TA and LG contributions were lower under HM than under SM, whereas ST contribution was higher under HM than under SM and MM. Gluteus maximus (GM) activation (0.38) and relative contribution (17.5%) were highest under MM, with a significant main effect of MH (p = 0.002). CONCLUSIONS: Midsole hardness altered selected lower-limb kinematics, navicular height, vertical loading rate, and muscle activation during running in children; however, these acute differences do not indicate functional superiority of any of the tested hardness conditions.