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This article is an excerpt of James Smith’s new book, Applied Sprint Training.
His book is based on a decade of research and experience and it deconstructs the theories and methodologies specific to applied sprint training, and its place in the training load. Thus, it relates to enhancing the competition outcomes of any sport that includes sprint efforts.
By James Smith
Regarding net force production, acceleration is the multiplier and thus its impact cannot be underestimated. The discussion of force, in this context, is incomplete without elaborating upon all of the forces (hence net force) acting on an object. Air resistance, gravitational pull, and friction are just a few of the factors affecting the sprint action. Most important, we must recognize the value of time dependent athlete generated force qualities being more relevant for sprint/acceleration development.
For example, an uninformed coach might mistakenly assume that more force, void of specification, at a given bodymass will enhance acceleration ability. This would result in the idea that simply getting an athlete stronger (maximally for example), provided bodymass is held constant, will result in greater acceleration ability. This is an incomplete notion. We must account for the fact that time is of the essence. Otherwise, the preparation of an athlete for the sole purpose of acceleration development may be limited to increasing the maximal force capability of the athlete and holding their bodymass constant. If only it were so easy…
The training problem of acceleration development is a variable one as the dynamics change with every step. As speed increases more force is generated at ground contact; however, as the speed increases there is less time to apply force.
During early acceleration, the ground contact times (GCT) are longer (because the acceleration is slower) and longer GCT provides more time to apply force. This is more forgiving for an athlete who, regardless of bodymass, is capable of generating high levels of explosive force. This is why an explosive athlete of greater bodymass (such as a shot putter or heavyweight Olympic weightlifter) can execute impressive sprint times over very short distances. Note that it is not the force production alone that is relevant here, but the rate at which these athletes are able to apply great forces.
Alternatively, as the acceleration increases, and GCT becomes shorter, the athlete has less time to apply force. Now the circumstances favour those with greater reactive/elastic qualities as the environment demands that more and more net force be applied to overcome the mass and as speed increases it becomes less and less possible for muscle/mechanical work to get the job done.
At this point is noteworthy to point out that there is a continuum of propulsive machinery; not harsh lines that divide the contributions of muscle/mechanical and reactive/elastic work. In this way, the discussion is similar to what will be presented in the applied physiology section regarding how there are distinct bioenergetic fuel sources; however, at no single time is any one bioenergetic fuel source responsible for muscle contraction.
World class biomechanists and coaches, such as Frans Bosch and Dan Pfaff, have elaborated upon the fact that reactive/elastic qualities are present from the very beginning of a sprint because even during early acceleration the sprinter demonstrates observable oscillations; and if oscillations are present so are reactive/elastic contributions. By contrast, there are no observable movement oscillations demonstrated during a tonic strength exercise such as a heavy deadlift; and thus the development of reactive/elastic qualities are not relevant towards improving a limit deadlift result.
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