Coach Dan Pfaff on Sprint Start Analysis from a Rear View.

Dan Pfaff analyzes a sprint start from a rear view, explaining how different parts of the body interact during acceleration.

"Stop stressing over the minutiae of the parts in the system you think you can control — and instead, work to better understand how the parts interact and interrelate to serve the common purpose of the system as a whole." Coach Pfaff’s commentary does exactly that – exploring the athlete as a system, and highlight the impact of how the parts of the system interact to influence the start. With that in mind, let’s consider the task – ‘accelerating the body from a static, starting position.’ The sprint start has two basic biomechanical requirements: First: Apply enough force down into the ground to support the body Second: Apply force backwards so the ground-reaction forces will propel the body forwards (Clark & Weyand, 2015) Recent research has demonstrated that, per Newton’s laws, sprinters who apply more horizontal force relative to body mass will attain the greatest initial acceleration (Rabita et al., 2015). However, an optimal balance of vertical and horizontal forces is required to achieve a desirable projection angle from the blocks, to ensure that the subsequent steps can be executed successfully.  Since gravity is always pulling downwards on the center-of-mass, the sprinter needs to project both out and up, in order to allow for the appropriate space and time for the limbs to correctly reposition in preparation for the next ground contact. In the initial steps after block clearance, ground contact times will get progressively shorter and flight times will get progressively longer as the sprinter gradually becomes upright. The body can only accelerate during the ground contact phase because force can only be applied when the foot is in contact with the ground. Therefore, flight time during initial acceleration should be just long enough to allow the limbs to properly reposition prior to the next ground contact, but without any extra time in the air. During the ground contact phase, the sprinter is challenged with applying sufficient vertical support force and maximal horizontal propulsive force in increasingly brief contact times. With this in mind, the mechanical goals of initial acceleration include: Prior to ground contact, limb in front of body attacks down and back toward ground Initial ground contact occurs underneath (or behind) the center-of-mass During ground contact, forceful extension of stance-leg and forceful flexion of swing-leg At toe-off, a projection angle that allows for maximal horizontal displacement with sufficient vertical displacement to reposition limbs in preparation for next ground contact Now that we understand the dynamics of the task, let’s consider the athlete’s interpretation of it. We have already briefly discussed that the control and coordination of movement is a result of the interaction of the task, the athlete, and the environment. Especially with young coaches, however, we tend to apply a one-size-fits all approach to the training of an athlete’s technique; rather than appreciating the i