Human joints

In my last blog, I focused on the importance of upper body strength training for runners. As important as upper body strength is for proper stability and prevention of injury, flexibility in this region is of equal, if not, greater importance in the prevention of injury. In order to properly discuss the importance of joint flexibility, my post today will attempt to provide you with a brief and elementary explanation of structure and function of human joints.

Every joint has a total angle of motion unique to the design of the articulating surfaces of the heads of the bones coming together to make up the joint. The only limiting factor in joint motion is the flexibility of both connective tissues and muscles of this region.

Muscle usually crosses a joint and connects to the bone by connective tissues referred to as tendons. Tendons consist of numerous layers of fascial tissue that provide the sheathing for every muscle fiber that makes up the muscle. They exit at the ends of each bundle of fibers becoming tendon, crossing the articular surfaces of the joint, and eventually merging with the tissue making up the sheathing over the surface of the bone called periosteum. During fetal development, all these connections are formed and is the reason injury to one select region can effect the whole body.

Connective tissue also is the material making up the both the ligaments and capsule surrounding most joints. The ligaments are strong reinforced bands within the structure of the capsule, which provide increased stability in all regions of increased stress during joint movement. The capsule provides not only additional stability to the joint, but also its inner membrane secretes the synovial fluid that provides both lubrication and nutrition to the slick surface cartilage covering the heads of the bone. In order for this fluid secretion to occur  providing flow over these surfaces, motion in the joint must occur.

I would like you to imagine the surface of a pond as my example to explain this motion. When the surface is calm and there are no ripples, it quickly becomes clogged with algae and other contaminants. However, when there is wind causing ripples on the surface, movement is occurring, and the pond remains fresh and clean due to the algae and contaminants not having the necessary stagnant environment in which to grow. All fluids in the human body react in the same way, and must have frequent periods of motion throughout the day to avoid the potential for chemical reactions that cause fluids to thicken and allow build up of contaminants to occur. Also like the function of a sponge, contaminants are squeezed out, and clean fluids taken in, by the effect of pressure on these tissues,

Flexibility exercises are one of the most important ways to provide this motion and limit loss of motion within the joints.