The core mechanism of muscle strengthening (in both volume and force dimensions) is stimulation and growth, and the subtle damage to muscle fibers during overloaded training triggers the repair mechanism. The secretion of growth hormone directs amino acids in the blood to muscle tissue, causing it to create new muscle cells and repair damaged cells, thus increasing the circumference and strength of muscle fibers. On the contrary, it is difficult to maintain muscles without stimulation. For the body, being able to store more energy is far more urgent than being good-looking and powerful, so it is more preferred to hoard fat desperately, while maintaining muscles also requires a lot of energy, which is not cost-effective and tends to weaken muscles quietly. In people who rarely exercise, the fastest decline is the lower limb muscles (especially the quadriceps femoris), which is nearly 30% lower than the upper limb.

The argument that "people's old legs decline first" is not without reason. Muscle mass begins to decline after reaching its peak around the age of 30. With age, collagen is decreasing, muscle fibers are broken and repair capacity is gradually lost, motor neurons are lost, hormone secretion is reduced, and muscles will become more and more inelastic. After the age of 40, the contraction amplitude, tension strength and control ability of muscles will obviously decline. If nutrition and exercise can not keep up, it is very difficult to maintain the number and strength of existing muscles. According to different characteristics, skeletal muscle can be divided into slow muscle fibers (red muscle fibers, type I fibers) and fast muscle fibers (white muscle fibers, type II fibers). Fast muscle fibers contract under the domination of neurons, with fast speed, great strength, short duration and easy fatigue. They mainly play a role in explosive sports such as sprinting or weightlifting.

The faster the muscle is used, the stronger it is, the less it is used, the muscle fiber volume shrinks and the number decreases, and the strength weakens. Slow muscle fibers rely on myoglobin for continuous oxygen supply, slow speed, small strength, lasting for a long time, not easy to fatigue, mainly in running and other endurance exercise function; relatively stable. Birds are mainly composed of slow muscle fibers, so they can do long flights. Muscles are recruited more in which exercise, and of course in which exercise they get more development.

If you want to exercise slow muscles, do aerobic exercise. If you want to exercise fast muscles, do anaerobic exercise that pays attention to strength and speed. The difference between the two types of muscle fibers is reflected in gender: men have more fast muscle fibers, strong bursts, and have an advantage during high-intensity exercise; women have more slow muscle fibers, strong muscle endurance, and the same weight can be repeated more times. Adapt to the advantages, foster strengths and avoid weaknesses of the exercise can bring twice the result with half the effort

The difference between the two muscle fibers is reflected in the individual: genes determine the different proportions of the two fibers in each person's body, which causes some people to have innate advantages in certain sports, but acquired exercise is difficult to change The ratio of the two can improve their respective efficiency and maximize their energy. For example, for two people with the same proportion of slow muscle fibers, the maximum oxygen uptake of athletes is generally much higher than that of non-athletes, and the advantage in endurance sports is naturally much higher. We are not for the competition of a certain event. Fast muscles and slow muscles must be exercised. Aerobic and anaerobic cannot be neglected. Under the condition of limited energy, we can achieve a rough balance of endurance, strength, and speed in order to maximize health benefits.

Professor Yoshiji Tanaka, who specializes in the relationship between aging and physical strength at the University of Tsukuba in Japan, summed up four muscle strength self-testing actions:

1. Shoulder muscle flexibility test

The left hand is raised over the shoulder, the elbow is bent down, the right hand is backhanded and the fingertips of the two hands are close to each other as much as possible. If the middle fingers of the two hands can touch each other, the score is "0"; If the two hands can overlap, the score is "1"; If the fingers of both hands cannot be touched, the score is "-1". Left and right hand exchange direction to do, and then calculate the average.

2. Waist leg muscle flexibility test

Sitting at the front end of the chair, straighten your right leg, heel to the ground, toe to the sky, bend your left leg, exhale and bend over, and straighten your hands toward your right toe. If the middle finger of the right hand can touch the big toe of the right foot, the score is "0"; if the fingertip can exceed the big toe, the score is "1"; if the fingertip can not touch the big toe, the score is "-1". The left and right legs are exchanged, and the average value is calculated.

3. Arm strength test

Stand on the wall with your arms wider than your shoulders, bend your elbows and your hands to support the wall, your feet are as wide as your shoulders, take a big step back, do the wall support action like push-ups, and test how many times you can do it in 20 seconds.

4. Leg strength test

Stand with your palms down and your elbows on your waist. Then lift your knees to palm height with your left and right legs. See how many times you can lift them in 20 seconds.

Test result ={0.041 × ① (height cm)} {0.017 × ② (height cm)} {0.154 × ③ (times)} {0.113 × ④ (times)}-6.094

Muscle age (years) =(-3.688 × test results) {0.832 × actual age (years)} 11.964

If the muscle age tested is more than 3 years older than the actual age, it is worth noting; if the value is small or negative, it means that your muscle foundation is not bad.

Grip strength is also a key index to measure the maximum strength of a person's overall muscle (it is also an important index to measure heart function and life span). The dominant hand naturally droops to hold the grip strength meter, holds it twice with maximum strength, takes the maximum value, and scores with reference to the following table, or evaluates by grip strength body mass index, grip strength body mass index = grip strength (Kg)÷ body weight (Kg)× 100, and generally normal grip strength index should be greater than 50.