Effect Of Footwear On Leg Stiffness Of Female Athletes

Abstract

Leg stiffness is a fundamental property of the lower limb spring pattern, and is expressed by the ratio of the maximum vertical ground reaction force (GRF) to the vertical displacement of the body’s center of mass. The foot-ground interface, i.e. the footwear (FW), is an important factor that contributes to the functional leg stiffness. PURPOSE:. To examine the FW effect on leg stiffness of young female athletes in a variety of team sports. METHODS: Twenty - six female basketball, handball and volleyball players (24.9 ± 6.1 years, height 176.4 ± 7.6 cm, body mass 71.0 ± 6.9 kg) performed 30 s of two-legged hopping in place, barefoot (BF) and with their usual FW, at a preset hopping frequency (digital metronome at 2.2 Hz which approximates the natural hopping frequency). Two-legged hopping was performed on a force platform (Κistler 9260AA, 1000Hz, Bioware Software 2812 A1-3) which was used to record the vertical GRF. The variables used for the statistical analysis of the FW effect were extracted from 10 consecutive hops, and were analyzed using two-way ANOVA (p<0.05). RESULTS: leg stiffness was significantly increased in the FW condition, both in absolute (BF: 32.7 ± 8.5 kN/m, FW: 36.9±8.3 kN/m, p = 0.014), as well as in relative to body mass values (BF: 0.478 ± 0.101 kN/m/kg, FW: 0.520 ± 0.110 kN/m/kg (p = 0.017). Also, despite the instruction to follow the same hopping frequency as set by the digital metronome in both the BF and the FW, hopping duration was shortened (BF: 0.469 ± 0.022 s, FW: 0.430 ± 0.013 s, p = 0.001) and the propulsive vertical GRF was increased (BF: 32.4 ± 4.7 N/kg, FW: 33.7 ± 5.6 N/kg, p = 0.048) in the FW condition. CONCLUSIONS: FW appears to increase leg stiffness, which may favor the myotendinous force transfer and contribute to a more effective lower limb spring pattern.