Measuring variation in vertical ground reaction force for football boot midsoles, playing surfaces and football specific movements

Abstract Excessive repetitive impacts in football are linked to chronic and non-contact injuries. Number of factors (extrinsic and intrinsic) play roles on such injuries. Purpose: Our study aimed to investigate the effect of midsoles, surfaces and specific football movements on peak vertical ground reaction force (VGRF). Materials and Methods: The studs of two football boots, artificial turf boots (ATB) and natural grass boots (NGB), used in this study were removed, after which the soles were smoothed and covered with abrasive paper. 17 male subjects 26 (±6) years old, 181(±7) cm, 79 (±11) kg performed two specific football movements (cutting 135° and penalty kick) on artificial turf (AT) and natural grass (NG) with ATB and NGB. The cushioning characteristics of the two football boots and resilience modulus of the two surfaces NG and AT were measured with an impactor machine and light falling weight deflectometer. Results: Peak VGRF was measured with insole measurement system for all possible conditions. Our findings determined that the ATB (softer midsole) generates greater VGRF (2.25BW) than the NGB (1.95BW) – an increase of 15%. In terms of the surface, the AT with higher resilience modulus results in higher VGRF. Moreover, the peak VGRF of the cutting movement (2.28BW) differed significantly compared to the penalty kick (1.99BW). Conclusion: Our results indicate that in boot-surface interaction, the effect of midsole boot cushioning on VGRF is more tangible than surface resilience. However, this study motivates boot developers to design a football boot based on all three variables: midsole hardness, movements and surface hardness.