Editor’s note: Although I have my own particular beliefs about the exact role of vertical and horizontal forces in sprinting, and related training cues and concepts, I do think that the emphasis on vertical force secondary to horizontal force is overblown in today’s training culture. Therefore, I’m excited to have a guest post on the topic by a legendary figure in the training community, Dr. Yessis.
It appears that the concept of production of vertical force is gaining a stronger foothold in the running community. However, can this concept be substantiated? I do not believe it can be. Running is a horizontal sport and the production of horizontal forces are much more important than unneeded strong vertical forces. For example it has been shown that upward (and downward) movement of the center of gravity of the world-class sprinter is only about 4 cm. It does not require great vertical forces to raise the body approximately 4 cm.’
Comments made in a recent post stated that recent research suggests that maximal vertical force production during top-end sprinting is a result of a rapid acceleration of the swing limb into the ground. But this cannot be substantiated by physics. When the swing leg is driven back into the ground the leg is moving backward and when it hits the ground it creates forces directed to the rear. Since every action has an opposite and equal reaction, the resultant force is horizontal speed forward.
To better explain, following are some excerpts from my book Explosive Running, second edition.
“Once straightened, (during flight) the leg immediately begins moving to the rear in preparation for touchdown. To pull the leg back and down (the pawback) the hamstring muscles, which were just placed on eccentric stretch as the thigh moved forward, contract with great force. At this time the hamstrings and gluteus maximus do their most important work. This is also the point where hamstring injuries often occur when technique is poor.
From physiology we know that when a muscle is placed on stretch it will contract with greater force. The stretching action that occurs when the thigh and shin swing forward enables the hamstrings to contract forcefully. As a result, when the swing leg touches down and becomes the support leg, the upper body is propelled forward.” This is the opposite and equal reaction. Almost all the forces are horizontal not vertical.
Also, “This backward leg movement and the following touchdown are very important in continuing fast forward movement of the upper body. At ground contact, the upper body can move in front of the support leg so that, when the pushoff occurs, the body will be as far out in front as possible. (See Fig. 3.14.) In this way the pushoff is directed more in a horizontal (forward) line, rather than projecting the body upward, as typically occurs in the heel hit.”
As you can see from the pictures the ankle joint undergoes extension creating positive horizontal ground reaction forces to propel the runner forward.
However, it is not uncommon to read that there are no propulsive forces at toe off. The pictures indicate otherwise. There are propulsive forces at toe off that contribute significantly to horizontal speed.
If anyone believes vertical forces are most important then they should substantiate the statement and explain how vertical forces can be converted into horizontal forces.
Michael Yessis is a teacher, sports performance trainer, biomechanist, and author. He earned a Ph.D. from the University of Southern California. He has done work translating, adapting, and implementing sports training methodology from the former Soviet Union, including work by Yuri Verkhoshansky, Anatoliy Bondarchuk, and Vladimir Issurin, for over fifty years. Yessis has worked extensively with professional and amateur athletes, including Todd Marinovich, Evander Holyfield, Dianne DeNecochea, Jose Luiz Barbosa, and others in over 50 years of active work. Yessis worked with the Los Angeles Rams and Los Angeles Raiders professional football teams, as well as Team USA Volleyball.
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