After attending a sprint performance workshop hosted by West Bromwich Albion Football Club, I felt that it would be a good idea to document some of the key concepts that I personally took from the presentation. I will focus on the presentation by Jean-Benoit Morin who is currently Full Professor at the Faculty of Sport Sciences of the University of Nice Sophia Antipolis (France). JB’s field of research is mainly human locomotion and performance, with special focus on running biomechanics and maximal power movements. He has published over 50 peer reviewed articles and collaborations with French sprinter Christophe Lemaitre and the French National football team are among his many achievements.
Force-Velocity Profile
Establishing the force velocity profile of an athlete is essential for individualized and specific training. The force-velocity profile quantifies the horizontal net force output, velocity and mechanical power of athletes, and their effectiveness of ground force application; sometimes also know as 'sprint acceleration mechanical profile'. The rate of force is highest during acceleration and will reduce as the amount of steps is increased. This is due to the horizontal force generated at the take-off slowly dissipating as the sprint continues, due the shift in the torso to a more vertical position. Therefore, the better sprinters are those that are more efficient at maintaining horizontal force.
In this respect two players could present with almost identical 40m sprint times, but could require totally different approaches in terms of performance improvement. Fig.1 shows the force-velocity profile of two players identifying this exact scenario. Both players performed a 40m sprint with almost identical times (player A – 6.21sec, player B – 6.37sec) at the same time displaying very different force-velocity profiles.
Whereas player A displays a higher force output at take-off, their ability to maintain that velocity is not as efficient as player B indicating high strength ability but a low ratio of force. In contrast player B displays a lower force output at take-off, but is able to maintain velocity a lot more efficiently showing good effectiveness but lower overall strength. This will have implications as to how both of these athletes approach a conditioning program, with player A maybe looking to focus on velocity based training and improving rate of force development, while player B focuses on max strength development. Without a force-velocity profile, it would be difficult to distinguish between these two players.
Quantifying The F∙V Profile
Unfortunately, it an arduous task actually obtaining the force-velocity profile. In JB’s studies, he has had access to some of the most advanced biomechanics laboratories in the world, which feature multiple force plates stretching along a linear track. This is completely inaccessible for the majority, although there may be a simpler solution. There is now an application available on iPad and iPhone (MySprint) which seems allow the accurate measurement of split times and runs the entire set of computations. There have been strong correlations between the results of the application and actual force-velocity profile tests – provided the app is used correctly; i.e. device must have a camera of at least 240 f/p/s.
Is Training Effective in Changing the F∙V Profile?
The answer to this is yes! The most effective approach seems to be resisted sled pulls. A systematic review into resisted sled sprint training did not identify any protocol with a resistance of over 30% of body weight. JB has been working on a non-published research project where participants sprint with a resisted weight of 80% their body weight performed over 20m two times a week over an 8 week period. Results so far have shown an increase in maximum force output, maximum power and maximum ratio of force.
Conclusion
Interestingly, JB’s research has also uncovered important information on players returning from injury. Studies have shown that on return from injury many players do not show a reduction in maximal velocity, although show a marked decrease in maximal force production and maximal power output. This can be beneficial in identifying return to player markers. Further research needs to be invested into developing a more functional way of measuring force output, which may be an interesting project if I was to pursue a MSc.
