Well, there are many muscles in the human body, which are composed of muscle fibers and tendons. Each muscle fiber is very thin, but many muscle fibers are tightly packed together. Tendons are located on both sides of the muscle fibers. A muscle generally has two tendons (such as biceps brachii), but there are also three tendons (such as triceps brachii) and four tendons (such as quadriceps femoris). Muscles are attached to bones. When a person wants to move, the muscle fibers contract or straighten, and the fibers pull or push the bones to move. When people do weight-bearing exercises, the muscle fibers in the exercised area are forced to contract or stretch. At this time, some muscle fibers will inevitably break (but don't worry, they can still grow back. These are only a small part of all your muscle fibers. ) situation. When you finish training your body, the human body begins its own repair work. Your body will use a large amount of protein and other nutrients to reconnect the broken muscle fibers. However, the reconstructed muscle fibers are not exactly the same as the original ones, but are thicker and stronger than the original ones. This is the instinct of human evolution. After each training session, some muscle fibers become thicker and stronger, and this is how human muscles become stronger. Under normal circumstances, the number of muscle fibers will not increase after a person reaches adulthood. Getting stronger after exercise is entirely due to the thickening of each muscle fiber. Sometimes, after multiple exercises, muscle fibers can grow to dozens of times their original thickness! Famous saying in the bodybuilding industry: If you ask a machine that can lift 100 kilograms to lift a weight of 120 kilograms, the machine will be scrapped; if you ask a person who can lift 100 kilograms to lift a weight of 120 kilograms, then this person will become able to lift 120 kilograms. Kilogram people! Therefore, only by constantly surpassing yourself can you become stronger! Of course, safety must be paid attention to. The intensity and time of exercise are also very different for people of different levels, because once injured, the gains outweigh the losses. In addition, muscle soreness during weight-bearing exercises and after exercise is not caused by muscle fiber breakage, but by the accumulation of lactic acid in the muscles. Lactic acid is secreted by the body itself and is used to protect muscles from injury (most people stop persisting when they feel pain). Only those who overcome muscle soreness and persist to failure during training can achieve the best results. After training, eat more alkaline foods such as vegetables to relieve this soreness.