Strength and function of intrinsic and extrinsic foot muscles: implications in sport performance

In human biomechanics the foot is a complex structure characterized by medial longitudinal and transverse arches compressing and recoiling during walking and running gait, sprints or jumps. Gradually modified during Evolution the foot is stabilized and mobilized by intrinsic and extrinsic muscles according to the specific demand of each activity. Acting as first human interface with the ground, the foot fulfils a dual role of load-absorbing structure and transmitter of the force produced at proximal levels of the lower limbs. Consequently many coaches, S&C coaches or physiotherapists do incorporate foot drills in their daily training sessions or clinical practice to improve athletes’ performance. However only few studies directly investigated the role of the foot muscles at both modulating the ground reaction forces and transmitting horizontal force. The aim of this thesis will therefore lie in providing elements of understanding on the strength and function of the intrinsic and extrinsic foot muscles and their implications in sport performance. The 1st part of the thesis will focus on the evaluation of the reliability and validity of two custom made ergometers created for measuring foot muscle strength in an active population. Taking into account muscle activity (EMG) and different ankle and metatarsophalangeal joints angulations will allow investigating the intrinsic/extrinsic muscles contribution during each tested position. The second part will aim at investigating potential correlations during explosive tasks like sprinting, cutting and vertical jump 1. between foot function (force, stiffness, flexibility, morphology) and general biomechanical variables of the force-speed profile (F0, V0, Pmax, RFmax) and 2. between foot function and specific kinetic variables (e.g. horizontal force, plantar pressures, contact time). Finally, the last chapter will concern the effects on the above-mentioned correlations of a 6-weeks foot strengthening protocol in athletes.