How the Body's Joints Work as a Function of Mobility or Stability

In the past decade, a new paradigm has become more and more prominent in the world of fitness and health. For decades, people would train various muscles, often in isolation from each other. Then, the trend became focusing on movements, not muscles. This was an important step forward in training philosophy and a better way to view how the body works as a whole, but it still did not go far enough. Now the focus has become on the joint functions of the body, which is an entirely new way of looking at training for high performance while maintaining good health and movement patterns.

Essentially, the new training paradigm recognizes that the body is basically one joint stacked on top of the other, with different features for each joint. Each of the joints has a primary purpose of either providing stability or mobility for the rest of the body. And the joints usually have opposite functions as one moves up or down the body. While each joint has certain features of both stability and mobility, each specific one has a primary purpose.

Starting from the bottom, the ankles provide mobility, especially moving forwards to backwards. There is a large range of motion in the ankles, which allow for various movements like running, sprinting, and moving from side to side. This is why it is often a mistake for athletes to tape their ankles to be more stable before competition, as the ankle is meant to move freely in a large range of motion.

The knee, on the other hand, is built to be stable. All it does is open and close, as it is a hinge joint. The knee does not have the ability to move very well in different planes of motion. In fact, when the ankle or hips push the knee out of alignment, serious injury can result with ACL tears, IT band pain, or patellar tendinitis. Thus, it is important to keep the muscles and connective tissues strong to provide stability to the knee.

The hip is very mobile and able to move forward and backward, out to the side, and make circular movements. It is a ball-and-socket joint, which gives the bones and muscles a large range of motion in various planes. If the hip is lacking in mobility, it can often cause pain at the knee or lower back as the body seeks to restore the balance.

The low back, then, is designed for stability. There is little range of motion in the lower back. The main function of these joints is providing stability and transferring force from the hips through the abdominal muscles and into the upper body. A lack of mobility at either the hip or the upper back can actually lead to back pain and injury.

The upper back is meant to be very mobile. It can bend further forward and backwards relative to the lower spine, and it has a greater twisting ability. While too much twisting or bending can injure the discs and connective tissues of the upper spine, it is still built for more mobility than the low back.

The shoulders are a quite special joint, in that they are made up of two parts. The shoulder blades -- or scapulae -- are meant to provide stability to the upper back and neck regions. The glenohumeral joint (where the shoulders connect to the upper arms), though, is much more mobile, as it can move backwards and forwards, out to the side, and has a large range of motion in various directions at once.

When trainers and athletes begin to understand how the body works as a series of joints, it becomes much less mysterious how injuries occur and how to prevent them. If a joint is built to be mobile but is lacking in range of motion, it may be necessary to work on increasing the range of pain-free movement before strength training.

Additionally, if there is pain in one joint, it is quite easy to look at the joints directly above and below to find the source of the problem. A lack of ankle mobility can lead to knee pain. Lack of hip range of motion causes damage to the lower back. This way of looking at how the body is built to function can help athletes prevent undue tissue damage and work on solving the causes of previous injuries.