18 years old and under 35 years old. The most important thing is to have smooth muscle. If you want to build muscles with clear lines, you need to meet the following two points:

1. On the premise that the training action reaches the standard, use heavy weight for resistance training, and control the weight at 8~ 10RM. Use 3 movements for each part, and try to do 3 groups for each movement, which can fully stimulate muscle cells.

2. The body fat rate should be at least below 13% (even lower), because the fat is in the upper layer of muscle. If there is too much fat, the muscles will be covered and the muscle lines will not be obvious. Therefore, aerobic exercise should be added during exercise.

In addition, taking muscle-building powder can solve the problem that the daily diet can't meet the energy demand. Muscle-building powder is convenient to eat and tastes good. However, the use method, dosage and time of muscle building powder must be scientific and reasonable. If used improperly, it will get twice the result with half the effort. To sum up, it can be summarized as two points: diligent practice and reasonable diet!