1/19/18 NASE Blog Post: Although expensive force plate technology has been around for decades in the labs of researchers, it is now beginning to find its way to university and professional sports teams. Researcher Weyand and colleagues, for example, have used a treadmill-mounted force plate to measure ground reaction force (GRF), rate of force production (RFP), and swing time between stance periods of the same foot for years in their innovative studies on sprinting. According to Carl Valle, “providers of force plate systems and services are growing in popularity—Sparta Science, P3, Andy Franklin Miller, and more. Accelerometer-based products like Bar Sensei and Push have made efforts to capture force production in the weight room.
The ability of the human body to generate maximal power is linked to a host of performance outcomes and sporting success. Power-force-velocity relationships characterize limits of the neuromuscular system to produce power, and their measurement has been a common topic in research for the past century. Unfortunately, the narrative of the available literature is complex, with development occurring across a variety of methods and technology. This review focuses on the different equipment and methods used to determine mechanical characteristics of maximal exertion human sprinting. Stationary cycle ergometers have been the most common mode of assessment to date, followed by specialized treadmills used to profile the mechanical outputs of the limbs during sprint running. The most recent methods use complex multiple-force plate lengths in-ground to create a composite profile of over-ground sprint running kinetics across repeated sprints, and macroscopic inverse dynamic approaches to model mechanical variables during over-ground sprinting from simple time-distance measures during a single sprint. This review outlines these approaches chronologically, with particular emphasis on the computational theory developed and how this has shaped subsequent methodological approaches. Furthermore, training applications are presented, with emphasis on the theory underlying the assessment of optimal loading conditions for power production during resisted sprinting. Future implications for research, based on past and present methodological limitations, are also presented. It is our aim that this review will assist in the understanding of the convoluted literature surrounding mechanical sprint profiling, and consequently improve the implementation of such methods in future research and practice.
Coaching Application: Force plate technology is still in its early stages of development and doesn’t do much more than measure the amount of force that an athlete transfers to the ground over time (GRF and ground contact time GCT) when integrated into a high speed treadmill as with the Weyand studies. Ground reaction force and GCT are two major determinants of speed during the start, acceleration, and maximum speed phase of a short sprint and the ability to measure these values each time the foot strikes the ground is invaluable. Pre- and post-testing following various training programs and exercises can identify the most effective means of increasing both vertically and horizontally-directed GRF, and identify force imbalances between the right and left limbs. However, until equipment costs are lowered and the accuracy and sophistication of force plate technology improves, coaches and athletes should continue to use the field tests described in various issues of Sports Speed Digest to provide estimates of absolute and relative ground reaction force.
References: Cross, Matt R., Brughelli, Matt, Samozino, Jean Benoit Morin. 2017. Methods of Power-Force-Velocity Profiling During Sprint Running: A Narrative Review. Sports Medicine, July, Vol. 47, Issue 7, 1255-1269.