henry copeland:

One or the other: Why strength training might come at the expense of endurance muscles -- ScienceDaily

This remodeling of the neuromuscular synapses during strength training results in the body developing more strength muscle fibers. "However, strength muscle growth occurs at the expense of the endurance fibers. More precisely, through the release of BDNF, the endurance muscles are transformed into strength muscles," clarifies Handschin. This makes BDNF a factor proven to be produced by the muscle itself and to influence the type of muscle fibers formed.
- www.sciencedaily.com