It was found that during accelerated runs, a typical support phase is characterized by a breaking phase followed by a propulsive phase (-FH followed by + FH). A common trend in the fastest subjects tested was that there was only a moderate to low amount of vertical force and a large amount of horizontal forces produced. Post study, it was hypothesized by the author that braking forces are necessary to store elastic energy in muscle and tendon tissue. This study loosely confirmed the importance of horizontal as well as vertical GRF during the acceleration phase of sprinting. Unfortunately, since data were collected at the 16-m mark, it was insufficient to draw definite conclusions regarding the entire acceleration phase. Morin et al. (2011)  performed a study to investigate the importance of ground reaction forces by having sprinters run on a force treadmill that measured both horizontal and vertical ground reaction forces. Belt velocity was measured for each step and calculations were performed to find the “index of force application technique”, which determines how well subjects are able to apply force in the horizontal direction. The second half of the test involved subjects performing a 100-m sprint on a man-made track using radar to measure the forward speed of runners to create velocity-time curves. The main result of this study showed that the force application technique (rather than simply the total amount of force applied) is the key determinant factor in predicting a sprinter's velocity. This has yet to be integrated into the governing equation of sprinting. The kinetics of running describes the motion of a runner using the effects of forces acting on or out of the body. The majority of contributing factors to internal forces comes from leg muscle activation and arm swing. The muscles responsible for accelerating the runner forward are required to contract with increasing speed to accommodate the increasing velocity of the body. During the acceleration phase of sprinting, the contractile component of muscles is the main component responsible for the power output. Once a steady state velocity has been reached and the sprinter is upright, a sizable fraction of the power comes from the mechanical energy stored in the ‘series elastic elements’ during stretching of the contractile muscles that is released immediately after the positive work phase. As the velocity of the runner increases, inertia and air resistance effects become the limiting factors on the sprinter's top speed. It was previously believed that there was an intramuscular viscous force that increased proportionally to the velocity of muscle contraction that opposed the contractile force; this theory has since been disproved. In a study conducted in year 2004, the gait patterns of distance runners, sprinters, and non-runners was measured using video recording.