Why strength training can be done at the expense of endurance muscles

The neurotrophic factor derived from neurotransmitter brain (BDNF) acts in the muscle, which decreases the number of muscle fibers during strength training. Researchers from the Biozentrum of the University of Basel have more closely studied this factor in the group of myokines and have demonstrated that it is produced by muscle and acts on both muscles and synapses. The results published in PNAS also provide new information on age-related muscle atrophy.

Fitness clubs are booming: new gyms are popping up like mushrooms. More and more people are trying to develop and strengthen their muscles. But what exactly happens in the muscle during training? In their recent work, the research group of Professor Christoph Handschin at the Biozentrum of the University of Basel has further investigated the muscles of force and the neurotrophic factor derived from myokine brain (BDNF), which plays an important role in the formation of muscle fibers.

The Handschin team has demonstrated that this factor is produced by the muscle itself and reshapes the neuromuscular synapses, the neuronal junctions between the motor neurons and the muscle. BDNF causes not only the development of muscle strength, but also the decrease in the number of muscle fibers in endurance.

BDNF acts on muscles and synapses

Generally, there is a distinction between two types of muscle, depending on the type of fiber they are composed of: there are slow-twitch fibers of endurance muscles, which are formed mainly during endurance sports . Marathon runners mainly exercise this type of muscle. The second form of muscle made of fast-twitch fibers is much less well studied. These strength muscles gain in volume during bodybuilding and provide substantial muscle power.

The Christoph Handschin team has now studied the hormone-type neurotransmitter of the myokine family in the mouse model. Myokines are released by the muscle during contraction. "It is interesting to note that BDNF is produced by the muscle itself and not only exerts an influence on the muscle, but at the same time it affects the neuromuscular synapses, which are the junctions between the motor neurons and the muscle. muscle, "says Handschin.

BDNF converts endurance muscles into muscles of strength

This remodeling of neuromuscular synapses during bodybuilding results in the body developing more muscle fibers. "However, muscle growth by force is done at the expense of endurance fibers." Specifically, thanks to the release of BDNF, endurance muscles turn into muscle forces, "says Handschin. This makes BDNF a proven factor that can be produced by the muscle itself and influence the type of muscle fibers formed.

Relevance for muscle training and age-related muscle atrophy

The new knowledge gained on BDNF myokine also provides a possible explanation for the decrease in endurance musculature observed as a result of strength training. This correlation is already taken into account in the training plan for high level sport. Muscle reshaping must be taken into account, especially in sports disciplines such as rowing, strength and endurance.

In addition, in a follow-up study, the research group found that in muscles without BDNF, the reduction in age-related muscle mbad and function is reduced. "We were not expecting this result," Handschin said. "This also makes the results interesting for the approaches to treating muscle atrophy in the elderly."