Muscle Flexibility

Muscle flexibility plays a vital role in normal mobility, one of the two primary areas of focus for sports injury rehab. In addition to joint mobility and accessory motions, flexibility of a muscle will determine how much range of motion is available. Not only that, but the tension of a muscle will impact how effectively it contracts, and the overall strength of the contraction.

Structure of Muscle

Muscles are made up of both muscle tissue and connective tissue. Microscopic myofilaments of actin and myosin make up the smallest components of muscle, the myofibril. Myofibrils are grouped together to create muscle fibers, and fibers are in turn grouped together to create facicles. Finally, fasicles are grouped together to create the muscle as we know it. Each grouping is surrounded by different layers of connective tissue, including the endomysium, perimysium, and epimysium.

You don't need to know all about the micro-anatomy of muscle to improve your flexibility. But we do have to remember that muscles are made up of both muscle fibers and connective tissues - which react to stress and stretching in different ways. This becomes important when deciding how to stretch to improve muscle flexibility.

Effects of Stretching

Warm Up For Best Results

Flexible, warm muscles are much less likely to be strained. Think of your muscles like a garden hose. In the summer months, when the hose is warmed by the sun, it is much easier to bend and shape. Now, take that same garden hose in January, and it becomes very rigid and doesn't bend as easily. Muscles are much the same, working best when warm.

Muscle fibers will stretch rather easily when not being contracted. It is the connective tissue sheaths that help to prevent damage by overstretching, and to give muscles their shape. They are also often responsible for flexibility problems. In order to improve flexibility, we have to get the muscles to relax, and create a controlled stress on the connective tissues.

Connective tissues will increase their overall length if an adequate stress is placed on them for a period of time. The tissues will lengthen, and that length will become a permanent change also known as a "plastic change". Lengthening of tissues that is not permanent is referred to as elastic changes. . The amount of time it takes to get these types of changes is much debated, but research suggests that 30 seconds of stretching, 5 days a week can improve muscle flexibility over a period of 6 weeks. This seems to be true whether you hold the stretch for 30 seconds straight, or do 6 repetitions of 5 second hold, with the total time being 30 seconds.

Types of Stretching

Flexible muscles allow for greater ranges of motion, as well as more strength and power production during activities. So how should you go about stretching?

Most people don't enjoy stretching - you may find it boring, or perhaps even uncomfortable if you have very tight muscles. So a shorter duration makes it a little more bearable. Regardless of whether you prefer long or short holds, the key is to stretch regularly. A routine of warming up and stretching prior to exercise is important not only to get the muscles ready for action, but also to improve and maintain long term flexibility. It should be part of any rehab, prevention, or performance program. For more on specific types of stretching techniques, use the links below.

Muscle Flexibility -- Return to Rehab Basics


Harvey L, Herbert R, Crosbie J. Does stretching induce lasting increases in joint ROM? A systematic review. Physiotherapy Research International. 2002;7:1-13.  

Bandy WD, Irion JM. The effect of time on static stretch on the flexibility of the hamstring muscles. Phys Ther. 1994; 74:845-852