How to utilize eccentric training

Every dynamic movement consists of three essential phases related to muscle activity: eccentric (lengthening), isometric (static), and concentric (shortening). These phases can significantly enhance sports performance when targeted individually. In this discussion, we'll dive into the first phase – eccentric training.

Eccentric muscle action, also known as the lengthening phase, involves the stretching of muscles due to tension. During this phase, the muscle attachments(distal and proximal) move in opposite directions. An example is the quadriceps during the lowering phase of a squat.

The Physiological Effects of Eccentric Training

Eccentric training focuses on two physiological components contributing to force production: the stretch reflex and the stretch-shortening cycle. The stretch reflex involves muscle spindles and Golgi Tendon Organs (GTO), serving as stimulators and inhibitors, respectively.

Muscle Spindles

Muscle spindles, located within the muscle tissue and aligned parallel to muscle fibers, serve as intramuscular sensory receptors. Their primary role is to transmit information to the brain and the central nervous system regarding the amount of force acting on the muscle. Through the afferent neural pathway, these spindles convey details to the brain about the necessary level of muscle contraction. The intensity of the spindle's signal correlates with the subsequent contraction signal generated by the brain through the efferent neural pathway. Importantly, the muscle itself remains unaware of specific activities, such as lifting weights, engaging in sports, or other movements. Instead, its sole focus is on impeding the eccentric lengthening of the muscle. In essence, the fundamental purpose of the muscle spindle is to tell the brain how hard it must contract to overcome a load.

Golgi Tendon Organ

In contrast to the muscle spindles that inform the brain about the required muscle contraction intensity, the Golgi tendon organ (GTO) plays a role in signaling when the muscles should relax. Situated within the tendons, the GTO differs from muscle spindles by gauging changes in the force applied to the muscle rather than changes in muscle length. To prevent the muscle tissue from exerting excessive force beyond the tolerance of connective tissue (tendons and ligaments), inhibitory mechanisms come into play.

During an eccentric movement, if the applied force is too great, the GTO activates an inhibitory muscle reflex, prompting relaxation to avert potential damage to the muscle structure. An illustrative example is dropping a weight during a lift when the force surpasses the body's capacity to handle it. Nevertheless, it is known that this mechanism can be overridden, allowing individuals or athletes to generate force levels significantly higher than their "normal" maximum. Superhuman strength has been seen more than once when, such as a mother lifting a car to rescue her trapped child. However, deactivating the autogenic inhibitory mechanism (GTO) in such cases resulted in notable damage to the muscular structure.

While the GTO is generally perceived as something good, it can be seen as an overprotective mother. Most GTO functions as a safety switch, set approximately 40 percent below the threshold where severe damage might occur to muscular structures. Training the GTO can enhance its ability to generate more force. An untrained GTO, however, poses limitations on explosive power as it hinders the athlete's potential to absorb high levels of force. When training the eccentric phase of dynamic movements, you are training these two proprioceptive structures of the muscles. To maximize an athlete's force production, an athlete must use methods in training that will decrease the inhibitory effect of the GTO and, at the same time, maximize the nerve signal response of the muscle spindle. If an athlete isn't used to handling high levels of eccentric force, the resulting concentric muscle action will be weakened(i.e., force production).

Stretch-shortening Cycle

The athlete who can eccentrically absorb more energy(kinetic energy) will be able to produce more force concentrically and therefore take advantage of the second physiological muscle action - the stretch-shortening cycle(SSC).

Consider the motion of stretching a rubber band – the stretching process generates "energy" that allows the band to revert to its original length. The SSC within the muscle and tendon as it relates to the eccentric phase works in a similar way. Kinetic energy is produced and stored when both the muscle and its connecting tendon is lengthened. This stored energy becomes available for utilization during the subsequent concentric phase. This phenomenon is commonly referred to as elasticity, signifying the ability of a structure to return to its original length after undergoing lengthening.

It is essential to understand that the energy that can be absorbed by the SSC is dependent on the combined effect of the stretch reflex and the GTO. The sum difference between the stretch reflex and GTO reflex determines force production, with the remaining energy absorbed by the stretch-shortening cycle.

Stretch reflex - GTO reflex = Force production.

The ability to load force eccentrically is directly proportional to force application.

How to Apply Eccentric Training

Eccentric specific work is extremely taxing on the nervous system not only for the physiological components just discussed but also the stress that it puts on each motor unit. When applying eccentric training, it should be implemented at the beginning of a workout when the nervous system is fresh. Athletes with less experience should limit eccentric training to large compound exercises, while experienced athletes can incorporate it more throughout the workout.

Load	Total Time of Eccentric(seconds)	Rep Range	Sets
85%	5-6	1-2	1-2
80%	5-6	2-3	2-3
75%	6-8	3-4	3-4
70%	6-8	4-5	4-5
65%	6-8	5-6	5-6
60%	6-8	5-6	5-6

Summary

In summary, an athlete that can produce more force, 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 during the concentric phase. Eccentric training has to be later combined with more isometric and concentric focused training as well as high-velocity training, since sport is about producing more force in less time. Strength is not what sport is about. While strength is essential, its application at high velocities is crucial for sports performance.