MODIFYING MIDSOLE STIFFNESS of BASKETBALL FOOTWEAR AFFECTS FOOT and ANKLE BIOMECHANICS.

Background: There is a growing incidence of foot injuries in basketball, which may be from the sport's repetitive, forceful multi-directional demands. Modifying midsole stiffness of the basketball shoe has been reported to alter ankle motion and plantar forces to reduce the risk of injury; however, the effects on anatomical, in-shoe foot (metatarsal), motion is not well understood.

Purpose: The purpose of this study was to identify differences in foot and ankle biomechanics between basketball shoes with differing midsole stiffness values during single-leg jump landings. It was hypothesized that a stiffer midsole would elicit lower 1 metatarsophalangeal joint (MTPJ) dorsiflexion angles, higher ankle dorsiflexion angles, and higher plantar forces and relative loading in the distal foot.

Study Design: Experimental cross-sectional study.

Methods: Twenty high school and collegiate-aged basketball players performed a single-leg side drop jump and a single-leg cross drop jump in a pair of standard basketball shoes and a pair of shoes modified with a fiberglass plate to increase midsole stiffness. Three-dimensional motion analysis and flexible insoles quantified foot and ankle kinematics and plantar force distribution, respectively. Separate 2 (footwear) × 2 (task) repeated measures ANOVA models were used to analyze differences in 1) ankle kinematics, 2) 1 metatarsophalangeal kinematics, 3) maximal regional plantar forces, and 4) relative load.

Results: The stiffer shoe elicited decreased peak ankle plantarflexion (mean difference = 5.8 °, = 0.01) and eversion (mean difference = 6.6 °, = 0.03) and increased peak ankle dorsiflexion angles (mean difference = 5.0 °, = 0.008) but no differences were observed in 1 MTPJ motion ( > 0.05). The stiffer shoe also resulted in lower peak plantar forces (mean difference = 24.2N, = 0.004) and relative load (mean difference = 1.9%, = 0.001) under the lesser toes.

Conclusions: Altering the midsole stiffness in basketball shoes did not reduce motion at the MTPJ, indicating that added stiffness may reduce shoe motion, but does not reduce in-shoe anatomical motion. Instead, a stiffer midsole elicits other changes, including additional ankle joint motion and a reduction in plantar forces under the lesser toes. Collectively, this indicates that clinicians need to account for unintended compensations that can occur throughout the kinetic chain when altering a shoe property to alleviate a musculoskeletal injury.

Level Of Evidence: 2b.