Core training has always been an important part of physical training. The core is the central axis of the human trunk in a broad sense, and in a narrow sense, it is the area above the pelvic floor muscles and below the diaphragm. In traditional martial arts, it is the place where the three horizontal fingers under the navel of the "dantian". The core area will be anatomically prone to instability, because there is no bony support around the lumbar spine like the ribs and pelvis, and only the surrounding muscles can provide support and stability. According to the type of muscle fibers, the muscles of the human body are divided into white muscle and red muscle. Type I muscle fibers have long-lasting endurance but weak output. Type II muscle fibers have poor endurance but have a higher output of force. 
Studies have found that muscles with many white muscle fibers are located on the surface of the skeletal muscular system, which mainly causes rapid joint movement and outputs force. On the other hand, muscles with more red muscle fibers are located in the deep layers closer to the joints, mainly to maintain the stability of the joints and output posture. It is based on our understanding of the functions of different muscle groups that the core is divided into the outer core and the inner core.
Classification of core muscles, outer core: gluteus maximus, erector spinae, rectus abdominis, internal and external oblique muscles, iliopsoas muscles, latissimus dorsi. Inner core: diaphragm, pelvic floor muscles, multifidus muscles, transverse abdominis muscles. The core area involved in the movement of the trunk is: forward flexion, backward extension, left and right lateral flexion, and horizontal anti-rotation. 1. From the perspective of the part and the whole of the human body: the stability of the core is the basis for the flexibility of the limbs. 2. From the perspective of motor development, it is the establishment of the rigidity of the core that allows us to crawl.
3. From the perspective of force mode, the core is the channel for the transmission of lower limb strength to the upper limb, which needs to be stable in order to be smooth.
4. From the perspective of myography, there are more near-fixed contractions than fixed contractions. The development of muscles is from the trunk to the limbs, and if the core is unstable, it should be fixed without fixation. In addition to not being able to exert maximum strength, it is also easy to cause sports injuries to the limbs.
Based on these theories, we should build a strong core.
The use of interval training in sports activities.
Be wary of training suspension syndrome after the Olympics.
Fitness starts with brain strength, and the order of muscle recruitment is very important.
Good sports performance is indispensable for gluteal training.
Discomfort in the knee joint, possibly gluteal weakness.