Effects of eccentric training on muscle adaptations

By Pierre-Luc Dubé

An often-overlooked parameter is the tempo used when performing an exercise. The different types of muscle contraction (concentric, isometric, and eccentric) each have their advantages and disadvantages, depending on the context in which they are used. However, beyond the soreness caused by eccentric work, it seems that the use of this type of contraction has additional advantages in terms of possible adaptations on the muscle cells and more specifically on the physiological and neural levels.

The mechanical stress created by the combination of stretching and the production of force causes changes to the internal environment, in addition to promoting more micro-lesions. Damage or changes to the cell lead to the release of certain factors such as insulin-related growth factors (IGF), which have the job of interacting with DNA in order to generate the transcription of messenger RNAs. Factor binding initiates and modulates the production of specific proteins. In addition, eccentric work would promote the presence of a greater number of androgen receptors and modify their actions, which would amplify the response to training and the gains in muscle mass.

Like the concentric contraction, the eccentric contraction creates tension inside the muscle which promotes ischemia by compressing the blood vessels. Similarly, factors like hypoxia-induced factors (HIF) are then released to respond to the lower oxygen environment. They act on the same principle as the IGFs mentioned earlier and induce a multitude of adaptations such as the increase in muscle mass, the acceleration of the degradation of necrotic tissue by macrophages, the increase in the number of red blood cells and increased cell proliferation. The stretching of fibers under tension also affects extracellular structures such as collagen which results in acidification of the environment outside the cell and increases the breakdown of muscle cells. Thus, the process initiated beforehand is strengthened by this phenomenon.

From a neurological point of view, the eccentric phase would promote the activation of type 2 fibers of the muscles involved in a movement, compared to the concentric contraction. Knowing that type 2 fibers have a greater potential for hypertrophy, using this regimen of contractions increases the potential for mass gain. Cortical activity also appears to be increased by eccentric work due to the increased demand for movement control and the stretch reflex. In addition, it appears that eccentric training promotes earlier preactivation of the cerebral cortex compared to concentric work. This could therefore facilitate the recruitment of motor units and the coordination of synergistic muscles. The use of eccentric contraction would reduce the activity of the Golgi tendon organs, resulting in increased force production. So, by combining greater muscle recruitment and reducing the reflex effect of the Golgi apparatuses, maximum force production is increased.

In conclusion, eccentric labor seems to have a more pronounced influence on the physiological and neurological adaptations that come with training, compared to other types of contractions. Beyond the increased potential for muscle mass gain and recovery, movement patterns and muscle recruitment could be improved. Thus, the potential for force production could also be positively influenced.

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