Muscle Building Study: How Strength Training Robs Endurance

Muscle Building Study: How Strength Training Robs Endurance

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Strength or endurance? Only one of the two is going right

Why can't bodybuilders be successful in endurance sports like marathons or bike races, and can't marathoners lift weights? A current study solves the riddle of why extreme endurance and high strength cannot exist in humans at the same time.

A research team from the University of Basel provided deeper insights into muscle building in humans and showed for the first time how endurance muscles convert into strength muscles during strength training. According to the study, the increase in strength is inevitably associated with a loss of endurance. The results were recently presented in the technical journal "PNAS".

The body has two different types of muscles

Muscles can basically be divided into two different forms, which differ in the type of fibers. Slowly contracting fibers ensure endurance and fibers that contract quickly create strength. While the slowly contracting muscles are strengthened in endurance sports, the fast contracting muscles are encouraged during strength training.

Muscle building researched for the first time on a material level

What exactly happens in the muscle when it is subjected to strength training has so far been largely unclear. Researchers from Basel have now been able to understand muscle building on a material level for the first time, solving a long-standing puzzle. The so-called myokines were at the center of research. These are messenger substances that build muscles during strength training.

New messenger discovered during muscle building

Brain-derived neurotrophic factor (BDNF) is the messenger that ensures that muscles gain volume. This hormone-like messenger substance is formed by the muscle itself and released during the contraction. As research director Professor Christoph Handschin reports, BDNF ensures that neuromuscular synapses are reformed. This changes the connection between the motor neuron and muscle.

Building strength muscles comes at a price

What does this reshaping of synapses mean for building muscle? According to the study, this transformation leads to an increase in strength muscles as a result. Basically, however, strength muscles are not built up, but transformed - from endurance muscles. "More precisely, the endurance muscles are converted into strength muscles by the release of the BDNF," explains Professor Handschin. BDNF is thus an unknown factor that can be proven to influence muscle fiber shape.

Quiz solved

This finding also provides a possible explanation for why strength training results in reduced endurance performance. The relationship may affect sports that focus on strength and endurance, such as rowing, where such muscle changes can have a direct impact on performance.

New findings for age-related muscle loss

In addition, the findings open up a new approach to counteract the age-related loss of muscles. In further studies, the researchers found that the age-related decline in muscle mass takes place more slowly if there is no BDNF in the muscles. This is also reflected in the sporting achievements of seniors, who can achieve high performances in endurance sports for much longer than in sports that are based on strength. "Of course, it also makes the results interesting for therapeutic approaches for muscle loss in old age," the research director summarizes the study results. (vb)

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  • Muscle building: more repetitions or instead high weights during strength training?
  • Strength training protects the liver from deadly diseases

Author and source information

This text corresponds to the requirements of the medical literature, medical guidelines and current studies and has been checked by medical doctors.

Graduate editor (FH) Volker Blasek


  • University of Basel: Either - or: Why strength training is at the expense of endurance muscles (accessed: 07/25/2019),
  • Delezie, Julien / Weihrauch, Martin / Maier, Geraldine / u.a .: BDNF is a mediator of glycolytic fiber-type specification in mouse skeletal muscle, PNAS, 2019,