The measurement of sprint mechanics using instrumented treadmills

Abstract

Since sprinting involves very fast movement velocities (up to 12 m/s in the best athletes), experimental studies in this field have always been a technical challenge. Whilst sprint kinematics and distance-time or velocity-time variables were first described by the end of the 19th century, kinetics and especially ground reaction force and mechanical power outputs have remained unexplored until the 1970s and 1980s. Cutting edge laboratory installations now allow for full-length sprint acceleration studies (single or multiple sprint protocols) with track-embedded force plates. However, a significant amount of literature and knowledge has been previously established by the use of instrumented treadmills. These were first non-motorized and not directly measuring the ground reaction force (end of the 1980s), but the most up-to-date device allows investigation of sprint mechanics and three-dimensional ground reaction force during an accelerated run (from zero to maximal velocity). In this chapter, we will present the historical development of these devices, along with their advantages and limitations, and the main experimental results obtained with the motorized accelerated treadmill. In particular, we will present the key concept of mechanical effectiveness of ground force application, and how it is related to sprint performance. Furthermore, we will discuss the muscular underpinnings of the mechanical effectiveness; specifically the role of hip extensors. Finally, we will discuss the comparison between treadmill and track sprint performance and mechanics, including data from elite sprinters, and how current and future research on this topic will allow a deeper understanding of this seemingly simple yet complex motor task.