Muscle growth in relation to age – Human muscle growth is constantly changing with age and can be divided into three stages: rapid growth, relative stability and significant decline. In men, starting from birth, muscle growth increases year by year as the body continues to grow and develop, reaching its highest value at the age of twenty-five, and then declining slowly year by year. In women, the maximum value is reached around the age of twenty-two.

　　Adolescent muscle water content is higher than that of adults, while muscle protein energy material reserves are lower than those of adults, muscle fibers are thinner, muscle strength is weak, endurance is poor, and fatigue is easy. The younger the age, the greater the difference with adults. Therefore, younger adolescents are not suitable for prolonged, high volume and high intensity muscle training. Nearly youth, muscle growth is relatively stable, when the best results of high-volume, high-intensity training. In the period of significant decline in muscle training effect is relatively poor, but as long as the body is normal health, adhere to the appropriate muscle training can still achieve better results.

　　A, the anatomical basis of muscle growth

　　The thickness of the muscle determines the size of muscle strength, is a measure of the degree of muscle development, is the physiological cross-section of the muscle. That is, the number of muscle fibers in the muscle is large and thick, the physiological cross-section of the muscle is large, the muscle is developed. The physiological cross-section of muscle is greatly influenced by acquired factors.

　　Muscle is mainly composed of protein. Fitness training can make muscle fibers thicker, the physiological cross-section of muscle increases, the reason is that training can stimulate the muscle, so that the anabolic protein is more vigorous, thus providing material security for muscle growth.

　　Second, the physiological basis of muscle growth

　　The growth of muscle depends on the accumulation of long-term hard training. When training, the body tissue cells consume a lot of energy material, which can only be gradually recovered after training through rest and nutritional supplementation, so that anabolism exceeds catabolism. Recovery will exceed the original level in a certain period of time, which is called ‘over recovery. Practice and research have proven that the best results are achieved when the next training session takes place during the overload recovery phase. The amount of energy expenditure and the rate of recovery are closely related to the intensity of muscle activity. Within a certain range, the greater the muscle activity and the more intense the exertion process, the more pronounced the overload recovery.

　　The so-called ‘within a certain range’ means that the amount of exercise should not be too much, otherwise too much energy is expended and not easily recovered. Long-term overload can also lead to overtraining and even injury accidents. Only by grasping, using the law of recovery of excess, and observing the principle of gradual and orderly progress, can we make steady muscle growth.

　　Third, the biochemical basis of muscle growth

　　Regular fitness exercise people compared with ordinary people, the muscle energy substances adenosine triphosphate and creatine phosphate to more, more vascularity, acid resistance and anaerobic enzyme capacity. The higher the level of training, the greater the energy reserves, the greater the tolerance to exercise, and the greater the number of new capillaries in the muscle. The increase in capillaries increases blood flow to the muscles, speeds up metabolism, and increases muscle size. So only by adhering to long-term fitness training can you strengthen muscle substance metabolism, improve muscle energy reserves, make muscle fibers thicker and muscle mass greater