Original Article

European Journal of Applied Physiology

, Volume 111, Issue 10, pp 2547-2555

First online:

Repeated sprinting on natural grass impairs vertical stiffness but does not alter plantar loading in soccer players

  • Olivier GirardAffiliated withASPETAR, Research and Education Centre, Qatar Orthopaedic and Sports Medicine Hospital Email author 
  • , Sébastien RacinaisAffiliated withASPETAR, Research and Education Centre, Qatar Orthopaedic and Sports Medicine Hospital
  • , Luke KellyAffiliated withASPETAR, Research and Education Centre, Qatar Orthopaedic and Sports Medicine Hospital
  • , Grégoire P. MilletAffiliated withISSUL, University of Lausanne
  • , Franck BrocherieAffiliated withASPETAR, Research and Education Centre, Qatar Orthopaedic and Sports Medicine HospitalQatar Football Association, Qatar Olympic Committee

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Abstract

This study aimed to determine changes in spring-mass model (SMM) characteristics, plantar pressures, and muscle activity induced by the repetition of sprints in soccer-specific conditions; i.e., on natural grass with soccer shoes. Thirteen soccer players performed 6 × 20 m sprints interspersed with 20 s of passive recovery. Plantar pressure distribution was recorded via an insole pressure recorder device divided into nine areas for analysis. Stride temporal parameters allowed to estimate SMM characteristics. Surface electromyographic activity was monitored for vastus lateralis, rectus femoris, and biceps femoris muscles. Sprint time, contact time, and total stride duration lengthened from the first to the last repetition (+6.7, +12.9, and +9.3%; all P < 0.05), while flight time, swing time, and stride length remained constant. Stride frequency decrease across repetitions approached significance (−6.8%; P = 0.07). No main effect of the sprint number or any significant interaction between sprint number and foot region was found for maximal force, mean force, peak pressure and mean pressure (all P > 0.05). Center of mass vertical displacement increased (P < 0.01) with time, together with unchanged (both P > 0.05) peak vertical force and leg compression. Vertical stiffness decreased (−15.9%; P < 0.05) across trials, whereas leg stiffness changes were not significant (−5.9%; P > 0.05). Changes in root mean square activity of the three tested muscles over sprint repetitions were not significant. Although repeated sprinting on natural grass with players wearing soccer boots impairs their leg-spring behavior (vertical stiffness), there is no substantial concomitant alterations in muscle activation levels or plantar pressure patterns.

Keywords

Repeated sprint ability Foot loading Spring-mass model characteristics Electromyographic activity Soccer