Sprinting speed during all four phases of a short sprint is determined by the ratio of body weight/ground reaction force (maximum forces applied to the ground in relation to body mass). In theory, improvement occurs by altering one or both of these variables: eliminating excess body fat (weight loss) and/or increasing ground reaction force (GRF).
NOTE: NASE MEMBERS, For specific speed-strength training programs and exercises related to this blog, see the following issues of Sports Speed Digest: January 2016, May 2016, May 2015, Sept. 2014
Unanswered questions do exist concerning just how the faster runners apply greater mass-specific force to the ground. This and other related factors are analyzed in the study described below.
A study by Weyand revealed that sprint running performance can be investigated relatively simply at the whole-body level by examining the timing of the phases of the stride and the forces applied to the ground in relation to a runners body weight. Research using this approach has addressed a number of basic questions regarding the limits and determinants of human running speed. The primary differentiating factor for the top speeds of human runners is how forcefully they can strike the ground in relation to body mass. A general relationship between mass-specific force application and maximum running speeds results from the similar durations of the aerial and swing phases of the stride for different runners. Recent work has elucidated the mechanism by which faster runners are able to apply greater mass-specific ground forces in the very brief foot-ground contact times sprinting requires.
Weyand provides further clarification of how speed is improved: “The variation present in the patterns of ground force application for sprinters and non-sprinters alike can be predicted from body mass and three stride-specific parameters (contact time, aerial time and ankle acceleration) using an anatomically based two-mass model of the human body. These observations indicate that sprinters exploit a motion-based deceleration mechanism to maximize ground force application. To what extent the dynamic mechanism relies on intrinsic limb strength vs. motor control and timing precision remains to be determined.”
*Coaching Application: Two key objectives for speed improvement in team sport athletes is to utilize various forms of speed-strength training to increase ground reaction force (GRF) in both a horizontal and vertical direction, and to control body mass (weight and muscle) by eliminating excess fat and engaging in training programs that maximize strength gains with minimum muscle hypertrophy. Weyand also indicates that faster athletes exploit a motion-to-force mechanism during the impact portion of ground contact to maximize GRF and attain greater limb velocities before ground contact. In addition, the limb is stopped more abruptly upon impact. Ground contact time and aerial time are additional va the iables affecting speed of movement.
Read the entire article by pasting the information below into your browser to gain additional insight on ground force requirements, the speed with which force is applied, and how elite sprinters are able to strike the ground with more force than average sprinters. Dr. Peter Weyand is an outstanding researcher whose work has paved the way to modern day speed improvement training.
Weyand, Peter (2017) “FORCE, MOTION, SPEED: A GROUNDED PERSPECTIVE ON HUMAN RUNNING PERFORMANCE,” ISBS Proceedings Archive: Vol. 35 : Iss. 1 , Article 289. Available at: https://commons.nmu.edu/isbs/vol35/iss1/289