Stretching Muscle Physiology

Stretching Muscle Physiology

Stretching your muscles is very good for them. Stretching every day improves flexibility, enhances your athletic performance and reduces your risk for injury during other forms of physical activity. Stretching a muscle actually makes it stronger, according to the "Journal of Applied Physiology". Regular stretching exercises increase your range of motion and realigns tissue inside muscle fibers. The stretching action takes place deep within muscle tissue and at the points where muscles meet bones.


Bones protect your organs and provide support for your body. Skeletal muscles move bones along pivot points, or joints, through pairs or groups of muscles that act in concert to cause motion. Ligaments connect muscle to bone. Some muscles contract to pull bones while others relax to allow the motion. Stretching muscles enhances both contraction and relaxation phases by reorganizing muscle fibers so that they work in concert with one another.

Shrinking and Stretching

Muscles gain the force to move bones by a cumulative shrinking and lengthening effect. One shrinking cell cannot budge a bone, but hundreds of cells can bunch up a bit of tissue, and large areas of bunching tissue exerts enough force to move a bone along a joint. Stretching works the same way, in reverse. The current length of the entire muscle depends on the number of stretched fibers – a rise in the quantity of stretched fibers increases the amount a muscle can stretch.


Muscles are able to contract, lengthen and stretch because of their unique physiology. This property is known as elasticity. Muscles are composed of many strands of tissue known as fascicles, as seen in whole cuts of beef. Each fascicle is made up of bundles of muscle fibers which, in turn, contain tens of thousands of myofibrils. Myofibrils are thread-like structures that are able to contract, relax and stretch. Inside each myofibril are millions of bands laid end-to-end, known as sarcomeres, which are made from overlapping thick and thin myofilaments. When sarcomeres contract, the thick and thin myofilaments overlap, causing muscle contraction. Muscle contraction causes an increase in myofilament overlap.

Relaxing a muscle causes a decrease in myofilament overlap, which then allows muscle fibers to elongate. At this point, sarcomeres are at their maximum length. Any additional stretching motion applies tension to the ligaments connecting the muscle to bone. As the stretching motion increases tension to the connective tissue, collagen fibers inside the connective tissue align themselves along the same line of force as the tension.

Stretching one muscle causes a contraction in the opposing muscle and vice versa. For example, extending the leg to stretch the hamstring simultaneously contracts the quadricep. (The quad is responsible for the action of leg extension.) So, even while stretching, you are also contracting - the opposing muscle group(s). Lifting weights involves two kinds of contractions: concentric and eccentric. During the upward movement of a bicep curl, the bicep experiences a concentric contraction (muscle shortening), the tricep experiences an eccentric contraction (muscle lengthening). The opposite happens as the arm is extended during the eccentric phase of the exercise.


The motion of stretching a muscle realigns disorganized muscle and connective tissue fibers. Injuries and stiff muscles cause misaligned connective tissue fibers. Physical therapy includes stretching exercises specifically because of this fiber realignment action on injured connective tissue.