# Profiling Sprint Mechanical Variables From Simple Speed Measures. Robin Healy BRU The biomechanics research unit (BRU) utilises a variety of methods to evaluate sprint performance. A considerable amount of testing performed on athletes involve simple methods such as split times recorded over a given distance i.e. 40 m. In recent years a field method has been developed and validated by Samozino and colleagues that can model the force, velocity and power output of an athlete’s centre of mass (COM) during a sprint from a standing or block start using only five split times (10 m, 15 m, 20 m, 30 m and 40 m).

During the acceleration phase of a sprint the horizontal velocity – time curve of the athlete’s COM has been shown to follow a mono-exponential function. By applying this function, the athlete’s horizontal velocity can be modelled and by differentiation with respect to time the acceleration of the athlete’s COM can be estimated. The horizontal ground reaction force can then be calculated by multiplying the athlete’s mass by their acceleration.

Using this approach coaches can estimate the following useful variables that give much greater insight how much force and power an athlete can produce and also their technical ability to apply force during a sprint. The maximal theoretical horizontal force (F0) represents how much sprint-specific horizontal force is applied during the athlete’s initial push against the ground. The theoretical maximum horizontal velocity (v0) indicates the maximal sprinting velocity an athlete could attain if there no mechanical resistances e.g. air resistance. The maximal horizontal power (Pmax) is simply the greatest power output produced during the acceleration phase. The maximal ratio of force (RFmax%) is a measurement of the proportion of the total force produced that is applied horizontally and can be seen as an indicator of the maximal effectiveness of an athlete’s force application. The final measure is the index of force application (DRF) which indicates how well an athlete can limit the decrease in the RFmax% as sprinting velocity increases and thus defines the overall mechanical effectiveness over the course of a sprint.

These measures, in addition to simple split times, can give coaches a much richer insight into their athlete’s sprinting ability which can help them identify key weaknesses which can be addressed with appropriate training. Although this method may seem complex an excellent user friendly spreadsheet for sprint acceleration Force-Velocity-Power profiling and a step by step video tutorial have been published by Prof. JB Morin and Dr. Pierre Samozino. These are available here and here.

Robin Healy is a Lecturer in Biomechanics and he is currently finish his PhD in the Department of Physical Education and Sport Sciences at the University of limerick. Robin is a member of the Biomechanics Research Unit (BRU) and his research interests include the biomechanical specificity of resistance training exercises and their potential transfer to both acceleration and maximal velocity sprinting.  Contact Robin via email on robin.healy@ul.ie or Follow him on Twitter.

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