It is usually seen that the arms and thighs of weightlifters are getting thicker and thicker, while the arms and thighs of long-distance runners such as marathons are getting thinner and thinner, which is also a sport. Why is one getting thicker and the other getting thinner?

2.

The training of weightlifters is short-term and high-intensity, mainly to overcome external resistance. Muscle will undergo adaptive changes under long-term load, which is manifested in the thickening of muscle fibers, the increase of muscle physiological cross section and the increase of muscle volume. Muscle contraction is to generate greater strength to overcome external resistance. The main contradiction to be solved is to increase muscle strength and overcome external load.

3.

The training of marathon and other long-distance runners is a long-term low-intensity training, the main purpose of which is to improve the ability of muscles to provide energy for a long time. Through long-term training, muscle will have adaptive changes, which are manifested as the increase of the number and volume of linear solids (subcellular organelles that can synthesize energy substances) in muscle cells, but the decrease of muscle volume, the thinning of muscle fibers and the increase of linear solids per unit volume are beneficial to energy supply. The main contradiction to be solved is the long-term sustainable energy supply.