It is all very well having muscles all over our body to produce strength for movement, but without a means to apply the strength of our muscles to our skeletons, muscles would just be useless excess weight. The muscles are attached to our skeletons however, by tendons, which are literally bands of connective tissue which hold the muscles onto our bones. These are also sometimes known as sinews.
Like ligaments, which connect one bone to another bone, tendons are made out of the protein collagen, with several bundles of collagen combined together forming a tendon. In addition to collagen, tendons are also composed of cells called tenocytes and water. The tenocyte cells sit between the collagen strands and help to produce the material making tendons as well as repairing tendons.
However, unlike ligaments, tendons do not stretch, as their sole purpose is to transfer the force produced by the muscles to the skeleton. If the tendons stretched too much, some of the strength produced by the muscles would be used to stretch the tendons rather than moving the skeleton around.
Tendons also have a better supply of blood than ligaments, with blood vessels running with the strands of collagen, and branching out in places away from the main vessels. However, some parts of tendons often receive less blood than other parts, and this can lead to conditions such as tendonitis. Generally, these blood deprived areas of a tendon are those furthest away from the blood source, such as the capillaries branching out to the collagen fibre bundles.
If the tendons are overused, the collagen can develop small tears, made difficult to repair by the lack of blood supply. Generally, where there is less blood, the more prone to injury the tendon will be. Inevitably many of the tendons deprived of blood occur at the joints, furthest from the initial blood source of the tendon, which is often a contributing factor in conditions such as tennis elbow. The joints are also where the tendons are taxed most, as we move around, leading to the collagen tears in the first place, which then become a persistent irritation as the collagen fibres are slow to repair due to the lack of blood flow.
As exercise increases blood flow, strength training can be used to strengthen and maintain the tendons. The stronger the tendons, the less likely they are to be injured, which will also help to keep the tendons healthy with aging. Inevitably growing old usually leads to some sort of weight gain, and as the tendons have to move this weight, transferring the muscles power to the skeleton, they can become susceptible to injury if someone is overweight, as more strain is placed upon the muscles, and in turn the tendons.
Tendons vary from person to person, as some people have long tendons and short muscles, whilst others have short tendons and long muscles. This can limit how much muscle someone can develop, as a longer muscle obviously has more mass, and more potential to be made bigger. As such, people with short tendons will be able to develop more muscle mass, and in theory more strength. As the tendons are short, they are also more efficient at transferring the muscles’ strength to the skeleton.
References
http://orthopedics.about.com/cs/sportsmedicine/g/tendon.htm
http://www.wisegeek.com/what-are-tendons.htm
