23 Mar The relationship between force and speed in concentric and eccentric actions
Concentric actions happen when the muscle fibers are shortened. For example, when rising from a sitting position (the quads are shortened to extend the knees), or when the elbow is flexed, the biceps are the ones that shorten in order to produce movement. Eccentric actions are the opposite, as they happen when the muscle fibers are elongated. Using the same examples, the quads are lengthened to flex the knees when sitting and the biceps are lengthened when returning to the starting position of a bicep curl.
Now when the speed factor is added the muscle actions behave differently. The graph highlights that by increasing speed, the body’s ability to produce force in concentric action decreases, and the opposite in eccentric actions, since the body produces greater force when speed increases.
Understanding the differences in force potential between concentric and eccentric actions is essential, since any dynamic action can be considered difficult or effortless depending on the type of action required to produce the movement. This is important to understand as it applies to running technique. Concentric actions happen at the takeoff and push off moments when running, and eccentric ones happen when the body needs to absorb the force from the from the step drop. If we apply it in a sprint, it would be better for the action to be primarily eccentric since it produces a greater amount of force. While sprinting, concentric actions are limited since the muscles are less productive. However, we are missing here the factor of the shortening and stretching cycle, resistance, flexibility, technique and mechanics, conditioning, etc. but we leave it for another blog, since it is a topic that can be extended a lot.
It is also important to understand this, since it must influence the way of scheduling the training of our athletes. Concentric and eccentric actions are generally trained with dynamic overload. For relatively slower movements, training is done in a weight room using classic / basic weight training exercises. For faster movements, various forms of dynamic or plyometric exercises are used that focus on improving locomotion. And it should be noted that although the ability to produce static and dynamic force is critical to sprinting, the two are not directly related. It has been shown that an athlete’s ability to produce large forces in the static area does not guarantee that the athlete also has the ability to produce great forces in the dynamic situation.
This forces the training to be focused on the demands of the athlete. There are times when implementing static force is necessary, but without forgetting that it must be focused on improving those dynamic actions. This is what would lead to elastic force, or the shortening and stretching cycle. It is where plyometrics workouts or training with inertial systems are implemented.
In summary, for an athlete to maximize the potential of the limiting factor imposed by strength limitations, he must be endowed with large static, dynamic and potential elastic areas.
Mann, R., & Murphy, A. (2015). The mechanics of sprinting and hurdling. Ralph V. Mann.
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