SPRINT MECHANICS REVISITED
By Jeff L. Hoskisson
Assistant Track Coach
Western Michigan University
What makes one sprinter faster than another? Much of the discussion today centers around the different training methods used to achieve faster speeds. One area that we need to make sure we understand before talking about what kinds of activities we need to be using in practice is mechanics. What does the sprinter need to be doing during the stride to make them more efficient and faster?
Running fast is the direct result of the athletes stride rate and stride length. This is something that we have always known. The big question is how do we maximize both of these to achieve top-level performances in the sprints.
The reality of sprinting is that we cannot have a maximum stride length and stride rate and be our fastest. What is needed is a maximum stride rate with an optimal stride length.
Maximal stride rate is how fast we can produce one stride, or in the case of the 100 meters about 50 of them. Stride rate is dependent upon a number of factors including, strength and mechanics. In order to produce greater stride rates one must be able to execute the correct stride cycle as fast as possible and with optimal length. Optimal stride length is one that allows the athlete to execute the correct stride pattern in as short a timeframe as possible.
A closer look at each of these factors will aid in understanding this better.
Let’s start with stride length. Stride length is the distance from takeoff to touchdown of one stride. There are a number of key factors in determining the optimal stride length.First is the distance the foot contacts the ground in front of the center of mass attouchdown. If the foot is placed too far in front of the COM the athlete will create a breaking action in each stride. This action allows the athlete to apply more force to the ground but it will slow the athlete down because it will take the athlete more time to move the body past the foot and then get off the ground. How close to the COM does the touchdown foot need to be? The simple answer is as close as possible. Mann (1990), found that good elite (9.8-10.0) sprinters made contact with the ground at an average distance of about seven inches in front of the COM. Athletes in the 10.3-10.5 (poor elite) range land about eleven inches on average from the COM. This shortened distance from the COM also translates into greater horizontal velocity at touchdown. This means that the athlete is traveling faster as the body passes over the touchdown foot. Good elite sprinters are moving at 27.8 feet/second, while poor elite sprinters are moving at 22.0 feet/second.
Another action that takes place in the preparation to touchdown is the extension of the lower leg. As the takeoff leg moves forward to a position in front of the COM, the upper leg should be near 90 degrees, in relation to the track. As the upper leg begins to move in a downward back motion, the lower leg will begin to open. This should be allowed to happen naturally. If an athlete forces the extension of the lower leg, they will cause it to be overextended. This action causes the touchdown foot to be placed further in front of the COM than is desired. By allowing the lower leg to open as the upper leg is being pulled back into the track a better angle will be achieved at touchdown allowing the foot to be placed closer to the COM.
The second important part of the stride occurs at takeoff. It has long been held that the sprinter needs to drive off the ground with a complete extension of the takeoff leg. This again can produce extra force against the ground but delays the athlete’s ability to get into the next stride. Three key areas can be looked at to determine the quality of the stride at takeoff. These are lower leg takeoff angle, flexion and ankle cross. Each of these angles is discussed in relation to the upper leg. Takeoff in elite sprinters was found to be at 139 degrees, while in poor elite sprinters it was at 169 degrees. This means that the top sprinters are leaving the ground before the takeoff leg reaches full extension. The slower sprinters are coming off the ground closer to full extension, but even they are not reaching full extension. By getting off the ground sooner the sprinter is able to execute a more efficient recovery in preparation for touchdown of the next stride. As the leg is being recovered forward, the angle between the upper and lower leg should be as small as possible, this is the position of full flexion. In good elite sprinters this angle is around 34 degrees. In poor elite it is 46 degrees. What is the reason for this big difference? The longer the foot stays on the ground at takeoff, the less time that it has to reach full extension before it must be brought through to prepare for touchdown. The final area in examining stride length is ankle cross. Where does the ankle cross over the opposite foot as it moves forward in preparation for touchdown? In the good elite sprinters the ankle crosses the opposite knee at a 34° angle. The poor elite sprinter crosses with a greater angle of 46°. This means that the lower leg is already opening, as it is moving forward in the poor elites. This puts the poor elite sprinter at a bigger disadvantage to the good elite sprinter. The good elite sprinter is in a better position to be able to prepare for touchdown. By crossing over the opposite knee at a tighter angle the foot can be pulled through to a better position on the front side to allow the sprinter to keep their touchdown distance closer to the COM.
Stride rate is a fairly easy concept. It is a direct result of the sprinter being able to perform the sprint cycle described above correctly, or more near that of the good elite< sprinter. When this is achieved, the time that the sprinter spends on the ground is reduced allowing them to get through the stride faster. Ground time is the largest contributor to stride rate. It is known that almost all athletes spend approximately the same amount of time in the air during the sprint stride. The big difference comes in the amount of time spent on the ground. The goal of all sprinters should be to spend as little time on the ground as possible. In order to achieve this, the sprinter needs the necessary strength to get them through the correct cycle.
In preparing sprinters to run faster, proper training is necessary. One of the main components to proper training is understanding just what the athlete needs to do in relation to the correct execution of the sprint stride. By understanding the sprint stride it becomes easier to devise training activities to assist the athlete in perfecting their technique.
Mann, Ralph. The Mechanics of Sprinting, 1990. CompuSport. Orlando, FL.