Remember when you strengthen muscle, you also have the opportunity to strengthen connective tissue. Thus, as you are getting stronger, you are also reducing the chance of injury. -Nate
At both ends of every muscle, the fascia covering the muscle tapers to form a strong, rope-like length of connective tissue called a tendon, which is connected directly to one of your bones. One end, which connects to a relatively unmoving skeletal part, is the origin of the muscle. The point where it's attached to a moving bone is the insertion of the muscle. (The bicep's insertion is in the forearm, near the elbow.)
When a muscle contracts, it pulls its origin and insertion closer together. Often a muscle is attached to two adjacent bones whose ends are joined together in a closed, fluid-filled capsule known as a joint (your knees, elbows, shoulders and knuckles are all examples of joints). Contraction of the muscle creates movement around the joint, allowing the pushing and pulling motions that make up physical movement.
Because tendons, ligaments, bursal pads and joints all take longer to adapt to activity than muscle fibers, these connective tissues are particularly vulnerable to inflammation, tears or other injury, especially from any type of repeated movement, whether it's walking, hitting a tennis ball or typing at a word processor. Avoiding such overuse injuries is one of the keys to maintaining a lifelong exercise routine.
From John Hopkins Health
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Most often, this movement involves a shortening of the involved muscles, such as when you lift a heavy weight off the ground. This is called a concentric contraction. If the opposing force is greater than the muscle force however, the muscle may actually lengthen as it works to contract. For example, when you lower a heavy weight down to the floor, your bicep muscle lengthens even though it's tensing. This is called an eccentric contraction. Finally, if the muscle doesn't change length at all during the contraction, when you push against a stationary wall, for instance, the result is an isometric contraction.
Other types of connective tissue also help to create smooth, controlled movements. Ligaments are tough, elastic bands that connect the bones together and help stabilize a joint. The best way to think of ligaments is as tethers that hold the bones together at the joint. The ligaments help guide how the bones move in relationship to each other. Nerve receptors in the ligaments and tendons also send information to the brain, to help regulate the intensity of muscle contractions. Fluid-filled sacs, called bursas, cushion and lubricate your tendons as they slide back and forth over your bones.
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