Flexibility is the functional capacity of the joints to move through a full range of movement. Flexibility is specific to each joint of the body. Muscles, ligaments, and tendons largely determine the amount of movement possible at each joint. The ability to move a joint through its complete range of motion is important in athletic performance (e.g., ballet, gymnastics) and in the ability to carry out the activities of daily living. Consequently, maintaining flexibility of all joints facilitates movement; in contrast, when an activity moves the structures of a joint beyond a joint’s shortened range of motion, tissue damage can occur.
Flexibility depends on a number of specific variables, including distensibility of the joint capsule, adequate warm-up, and muscle viscosity. Additionally, compliance (“tightness”) of various other tissues such as ligaments and tendons affects the range of motion. Just as muscular strength is specific to the muscles involved, flexibility is joint specific; therefore, no single flexibility test can be used to evaluate total body flexibility. Laboratory tests usually quantify flexibility in terms of range of motion, expressed in degrees.
Poor lower back and hip flexibility may, in conjunction with poor abdominal strength/endurance or other causative factors, contribute to development of muscular low back pain; however, this hypothesis remains to be substantiated. Those with greater total body flexibility may have a lower risk of back injury. Older adults with better joint flexibility may be able to drive a car more safely. Engaging regularly in stretching exercises and a variety of physical activities that require one to stoop, bend, crouch, and reach may help to maintain a level of flexibility that is compatible with quality activities of daily living. Joint movement throughout the full range of motion helps to improve and maintain flexibility.
Optimal musculoskeletal function requires that an adequate range of motion be maintained in all joints. Therefore, preventive and rehabilitative exercise programs should include activities that promote the maintenance of flexibility.
Reductions in flexibility often are evident by the third decade of life and progress with aging. A lack of flexibility combined with a reduced musculoskeletal strength in elderly persons often contributes to a reduced ability to perform activities of daily living. Accordingly, exercise programs for elderly persons, as well as other populations, should emphasize proper stretching for all the major joints, especially for areas affected by a reduction in range of motion. Flexibility is highly individual, specific to each joint, and affected by many factors, including muscular strength and disease (e.g. carpal tunnel syndrome, arthritis).
Stretching can be defined as the systematic elongation of musculotendinous units to create a persistent length of the muscle and a decrease in passive tension. Musculotendinous units are considered the limiting structures preventing greater ranges of motion about the joint. Muscles have viscoelastic properties; that is, elasticity indicates that length changes are directly proportional to the applied force, and viscous properties indicate that the rate of muscle deformation is directly proportional to the applied force. The muscle’s viscoelastic property permits a gradual decrease in tension or force within the muscle at a given length. The attenuation of muscular tension over time is termed stress relaxation. The application of stretching can result in a continued deformation (longer length) of the muscle at a lower tension, which is commonly known as improved flexibility.
Although flexibility can improve acutely, there is a lack of scientific evidence as to how long the effect may last. Many experts recommend frequent (daily) stretching because flexibility is believed to be transient. Different types of stretching techniques (e.g., static, dynamic, proprioceptive neuromuscular facilitation [PNF]) can be performed. Static stretching involves slowly stretching a muscle to the end of the range of motion (point of tightness without invoking discomfort) and then holding that position for an extended period of time (usually 15 to 30 seconds). The greatest change in flexibility has been shown in the first 15 seconds of a stretch with no significant improvement after 30 seconds. The optimal number of stretches per muscle group is two to four, because no significant additional improvement in muscle elongation is evident in repeated stretching of five to ten repetitions. The risk of injury is low, requires little time and assistance, and is quite effective. For these reasons, static stretching is recommended.
Properly performed stretching exercises can aid in improving and maintaining range of motion in a joint or series of joints. Flexibility exercises should be performed in a slow, controlled manner with a gradual progression to greater ranges of motion. A general exercise prescription for achieving and maintaining flexibility should adhere to the following guidelines:
- Precede stretching with a warm-up to elevate muscle temperature
- Do a static stretching routine that exercises the major muscle tendon units that focuses on muscle groups (joints) that have reduced range of motion
- Perform a minimum of 2 to 3 days per week, ideally 5 to 7 days per week
- Stretch to the end of the range of motion at a point of tightness, without inducing discomfort
- Hold each stretch for 15 to 30 seconds
- Two to four repetitions for each stretch
It is recommended that an active warm-up precede stretching exercises. Some commonly employed stretching exercises may not be appropriate for some participants who may be at greater risk for musculoskeletal injuries because of prior injury, joint insufficiency, or other conditions.