Every dynamic movement consists of three parts as it relates to the muscles involved in the movement. We have eccentric(lengthening), isometric(static), and concentric(shortening). Training these three parts individually can be incredibly beneficial for sports performance and is often referred to as Triphasic training. Today I'll discuss the third part, Concentric training.
The concentric phase "is a type of muscle activation that causes tension on your muscle as it shortens. As your muscle shortens, it generates enough force to move an object. This is the most popular type of muscle contraction. In weight training, a bicep curl is an easy-to-recognize concentric movement."
The concentric phase is the measuring point of athletic performance. How far can you jump? How fast can you swim? How fast can you run? How much can you lift? These are all performance measures based on force output in the concentric phase. The concentric phase is the measure of an athlete's rate of force development(RFD).
The RFD of the concentric phase is assisted by two components that I discussed in the article regarding eccentric training, the stretch reflex, and the stretch-shortening cycle(SSC). The amount of potential energy stored within the musculoskeletal structure is dependant on the former eccentric and isometric contractions. That's why all three phases are connected.
An athlete who can quickly create energy and transfer is nothing if that energy can't be placed to produce force rapidly. Therefore, the real importance of the concentric phase is related to the synchronization of the entire muscle action(eccentric, isometric, and concentric), maximizing the energy from both the eccentric and isometric phase into an explosive dynamic movement.
Related to the concentric phase is intramuscular coordination and intermuscular coordination. Intramuscular coordination refers to the fibers of the same muscle group, while intermuscular coordination looks at muscle fibers between different muscle groups.
Here we're talking about neuromuscular adaptions such as the maximum number of units recruited(motor united recruited) and the frequency at which these muscles fibers are firing at(rate coding), read more details about this under my isometric post.
For athletes to generate a high level of concentric force, more muscle fibers need to be recruited and the need to fire at a fast rate to let the muscles reach their absolute peak force. This can be achieved best with isometric training but is crucial for concentric training.
One of many things that we're trying to improve with concentric training is intermuscular coordination, especially the inhibition of the antagonist muscle. The antagonist muscle is eccentrically contracting to deaccelerate the speed and the force of the concentric contraction to protect the joint from tearing. However, this defense mechanism is overprotective and must be detrained. If we can inhibit the antagonist muscle, it will result in maximal rate of force development(RFD).
The concentric phase is so a much more complicated motor task that the eccentric and isometric phase. That is because the dynamic phase requires a significant amount of coordination and synchronization between various neuromuscular systems to produce a high level of fore output. But as the other two phases, the concentric phase is a trainable skill. A well trained concentric phase build intramuscular tension more significant than that of the load imposed on the muscle structure.
The actual concentric contraction takes place between the stretch reflex and SSC. For explosive strength, all three have to fire in rapid succession, and synchronization is so important. An athlete's reactive ability is defined by the efficiency and speed with which the concentric contraction follows the introductory force output from the stretch reflex and, in turn, determines the amount of stored kinetic energy used from the SSC to improve overall force output. In other words, proper synchronization lets the athlete switch instantly from the eccentric to the concentric phase in a dynamic movement. The goal with concentric training is to lose as little force as possible from the stretch reflex acquired during the eccentric and isometric phases.
The most crucial thing when performing concentric focused work is to push against the bar as hard as possible, during its entire range motion. BE EXPLOSIVE! Here are some general parameters for eccentric loading:
If an athlete can produce more force, he can apply more force, simple as that. However, it is vital to notice that if you train slowly you'll become slow. Therefore, always maximize the speed and that is what concentric training is all about, training fast. Sport is about producing more force in less time. Strength is not what sport is about. Strength has a role in sport but is ineffective if it can't be applied at high velocities. Therefore an athlete who can produce more force and at higher speeds will have an advantage compared to someone that can't do it as well.
Example video of an explosive back squat.