Study Finds That Training Muscles for Strength May Lead to the Decrease in Their Endurance Capacity

The brain-derived neurotransmitter factor (BDNF) affects the muscles during strength training in a way that causes the number of endurance muscle fibers to decrease. Researchers at the Biozentrum of the University of Basel have studied this factor. They have demonstrated that it is produced by the muscles and has effects on both the synapses and muscles. The results of the study also provide new information on age-related muscle atrophy

Muscles Strength Endurance

Fitness clubs are flourishing and new gyms are sprouting like mushrooms and more and more people are trying to build up their muscle’s strength. But the big question is what really happens inside your muscles during training? Handschin of the Biozentrum at the University of Basel studied in more detail muscle strength and the myokine neurotrophic factor, which plays an important role in the formation of muscle fibers.

Christoph Handschin’s team showed that this factor is produced inside the muscle and that it can easily remodel the neural connections between motor neurons and muscles. BDNF not only causes the development of strength muscle fibers but also leads to a decrease in the number of resistance muscle fibers.

BDNF affects both muscles and synapses

In general, two types of muscles are distinguished according to the type of fiber they are made of: there are slow-twitch fibers for endurance muscles which are formed mainly during endurance sports. Marathon runners train mainly these types of muscles. The second type of muscle is made of fast-twitch fibers which unfortunately has been much less studied. These muscles gain volume during strength training and provide a particularly high level of muscle strength.

Christoph Handschin’s team studied the neurotransmitter from the myokine family in a mouse model. Muscles release myokines during contraction. “It is interesting that BDNF is produced by the muscle itself and not only exerts an influence on the muscle. At the same time, it affects the neuromuscular synapses, which are the junctions between the motor neurons and muscle,” says Handschin.

BDNF transforms endurance muscles into power muscles

This remodeling of neuromuscular synapses during muscle training leads to the development of additional muscle fibers. However, muscle strength increases at the expense of endurance fibers. More precisely, by releasing BDNF, endurance muscles are transformed into strength muscles. Indeed, BDNF is produced by the muscle and has been proven to influence the type of muscle fibers formed.

The importance of BDNF to muscle mass and muscle atrophy

The new knowledge gained about BDNF may also explain the decrease in endurance muscle strength due to muscle training. This correlation is already included in the training plan for competitive sports especially in bicycling and rowing, which emphasize strength and endurance.

In addition, the research group showed in another study that in muscles that don’t produce enough BDNF, the decrease in muscle mass and function related to age is limited. “We did not expect such a result,” explains Handschin. This, in turn, makes the results interesting for the treatment of muscle atrophy in the elderly.

References

Delezie, J., Weihrauch, M., Maier, G., et al. (2019). BDNF is a mediator of glycolytic fiber-type specification in mouse skeletal muscle. Proceedings of the National Academy of Sciences, 116(32), 16111-16120. https://doi.org/10.1073/pnas.1900544116