RM stands for the highest number of repetitions that a load can perform continuously. Here, 20-25rm means that the load can do 20-25 times at most.

1-5RM load training can thicken muscles and develop strength and speed; 6- 10RM load training can make muscles thick and strength speed increase, but endurance growth is not obvious; The muscle fibers of 10- 15RM were not obviously thickened, but their strength, speed and endurance were improved. After 30RM load training, the number of muscle capillaries increased, and the endurance was improved, but the strength and speed were not improved obviously. It can be seen that the load weight of 5- 10RM is suitable for bodybuilding training to increase muscle mass.