The nature of flexibility
Flexibility refers to the total range of motion of a joint or group of joints. Flexibility, which differs from person to person and from joint to joint, encompasses all components of the musculoskeletal system, as well as specific neuromuscular pathways of the body. The structural characteristics of the joints and the mechanical properties of connective tissues largely affect the extent of movement around a given joint. The specificity of movement that a person performs in regular physical activities and stretching methods often defines the development and improvement of the body's range of motion. The goal of all stretching programs is to optimize joint mobility while maintaining joint stability. Concern should always be focused on the systematic, safe and effective application of the range-of-motion techniques utilized.
The benefits of stretching
An examination of the reported research and empirical evidence support the following benefits of stretching:
-An increase in functional range of motion
-Reduction of low-back pain and injury
-Reduction in the incidence and severity of injury
-Improvement in posture and muscle symmetry
-Delay in the onset of muscular fatigue
-Prevention and alleviation of muscle soreness after exercise
-Increase in the level of certain skills and muscular efficiency
-Promotion of mental relaxation
-Personal enjoyment and gratification
Flexibility training has more recently been recognized among the other components of fitness as a means to better unify one's mind, body and spirit. Taking a similar approach to the harmony of the mind, body and spirit in yoga techniques, many health practitioners are using flexibility training as a vehicle to facilitate mental and physical relaxation and stress reduction.
Factors that influence flexibility
Distinctive connective tissues associated with any joint contribute to joint flexibility. With the muscles relaxed, and reflex mechanisms minimally involved, Johns and Wright1 have found the relative contributions of soft tissue to joint stiffness to be the following: joint capsule, including ligaments (47 percent), muscles and their fascial sheaths (41 percent), tendons (10 percent), and the skin (2 percent). Other factors which influence flexibility are:
Age. There tends to be a decrease in flexibility with aging.2 This is largely attributed to a loss in elasticity in the connective tissues, which go through a normal shortening process as a result of decreased physical activity. Due to this loss of joint mobility, older persons are more susceptible to injury from vigorous physical activity. Regular exercise, including stretching exercises, can minimize the effect of this age-related decrease in range of motion. Gender. Females tend to be more flexible than males of the same age throughout life.3 This difference is generally attributed to anatomical variations in joint structures.
Type of joint. It is very well established that flexibility is specific to each joint. For example, trained dancers demonstrate superior flexibility of the ankle and legs but only moderate flexibility in their upper torsos. The degree of range of motion at the joint is also affected by joint structure (e.g., ball and socket, hinge, condyloid) and the type of movement that the joint exhibits (e.g., flexion-extension, rotation, adduction-abduction, pronation-supination, protraction-retraction and circumduction).
Exercise history. Participation in regular exercise involving full range of motion generally enhances flexibility; on the other hand, a sedentary lifestyle often results in diminished flexibility.
Temperature. An increase in intramuscular temperature via a warm-up or the participation in physical activity will increase range of motion.4 A lowering in intramuscular temperature is associated with a decrease in flexibility.
Body build. The evidence leads one to conclude that factors including arm and leg length, arm span, height and weight do not significantly affect range of motion.
Resistance training. Resistance training in which exercises are executed through a full range of motion may help to improve a person's flexibility.(5)
Warm-up vs. stretching
The warm-up and stretching portions of a class should not be confused. The warm-up is physical activity that raises the temperature of the blood, muscles, tendons and ligaments. The goal is to prepare the body's freely moveable joint structures for vigorous physical activity while reducing the risk of injury.6 The warm-up is best accomplished with a full-body rhythmic activity such as low-to-moderate intensity aerobics, stationary cycling, walking or jogging. This segment, approximately five minutes in length, should be intense enough to increase body temperature, but not so demanding as to lead to fatigue. Often included after this full-body-movement phase of the warm-up are muscle/joint movements that include functional range of motion, holding positions usually no longer than 10 seconds.
Stretching exercises, to increase range of motion, are best presented after the cardiovascular cool-down or after the muscle toning section of class. The temperature of the soft tissues is most likely elevated, making this time in the workout ideal for increasing flexibility.
Methods of stretching
The types of stretching programs commonly used are classified in four general categories: passive, ballistic, static and proprioceptive neuromuscular facilitation (PNF). Passive stretching techniques are usually performed with an outside force such as a towel or partner who applies a stretch to a relaxed joint. Partner stretching requires close communication between partners and a slow application of the stretch is essential to prevent injuries. Ballistic stretching was popular in the 1970s, but is used primarily by athletes due to a greater risk of injury and lesser efficiency compared with other stretching techniques. With ballistic and passive stretching there is a need to control numerous factors to ensure safety, limiting the applications of these techniques.
At present, the two most accepted methods of improving flexibility are the static and PNF techniques. To date, neither technique has been demonstrated to be superior for improving range of motion. Each method operates on the premise that to increase flexibility and prevent risk of injury, the muscle being stretched should be as relaxed as possible.
Static, or hold stretching, is probably the most commonly used flexibility technique and is very safe and effective. With this technique, a muscle or muscle group is gradually stretched to the point of limitation, and then typically held in that position for a period of 15 to 30 seconds. Taylor, et al.,(7) reported significant improvement in flexibility using four sets of 15 to 20 seconds per stretch.
PNF stretching techniques are also effective in increasing flexibility. The PNF techniques were developed by Dr. Herman Kabat in the 1950s as part of his therapeutic work with patients suffering from paralysis and muscular diseases. In the early 1970s, L.E. Holt(8) introduced modifications of Kabat's work that were adopted by several athletic teams. Over the years these PNF concepts and modifications, when carefully introduced, have been applied by many personal trainers and fitness instructors with their students.
Two commonly used PNF stretching techniques, contract-relax and contract-relax agonist contract, may be readily modified and used either individually or with a skilled partner. In the first phase of both techniques, the target muscle group is placed on stretch. The next phase involves a five- to six-second less-than-maximal voluntary contraction in the pre-stretched muscle group. The contraction is "isometric" because movement of the body segment is resisted by the individual or partner. In the third phase of this technique, the contracted muscle group is first relaxed, and then stretched to a new point of limitation. With the agonist contraction, the client now contracts the opposing muscle(s) for five to six seconds against a resistance. In the final step, the agonist contraction is released and the target muscle group is taken to a final stretch. Researchers have found this technique to be superior to the contract-relax technique for improving range of motion.(9)
Sensory response to stretching
When a muscle is stretched, receptors within the muscle, known as muscle spindles, are stimulated and send a message to the spinal cord that the muscle is being extended. If the muscle is overstretched, or stretched too fast, the spinal cord, in response, sends a reflex message to the muscle to contract. This is a basic protective mechanism, referred to as the stretch reflex, to help prevent overstretching and injury. This reflex helps to explain the risk in ballistic stretching. The speed of bouncing during ballistic stretching may illicit an equally responsive contraction of the muscle, leading to strain in the musculotendinous area and microscopic tearing of muscle fibers.
Located in the musculotendon junction is another sensory receptor called the golgi tendon organ. When enough tension is created in the muscle from either a deep stretch or a muscle contraction, the golgi tendon organ triggers a reflex known as the inverse stretch reflex. This reflex inhibits muscle contraction and relaxes the muscle. Thus, the golgi tendon organ is part of a defense mechanism that prevents the muscle from developing too much tension, which may lead to injury.
The muscle's sensory receptors (muscle spindle and golgi tendon organ) provide a means of monitoring and maintaining an optimal and safe operating range of motion for the muscles. The muscle spindle causes the muscle to contract when too much stretch, or too fast of a stretch, is initiated, while the golgi tendon organ produces an inverse stretch reflex, which relaxes the muscle when too much tension is produced.
Technique in stretching
The results of a recent study demonstrate the importance of technique in a stretch. Sullivan, et al.,10 found that the effect of the pelvic position (i.e., anterior pelvic tilt vs. the posterior pelvic tilt), in a hamstring stretch significantly affected the range of motion at the hip joint. (The anterior pelvic tilt proved to be the preferred anatomical position.) The implications of this research are clear. Instructors who are knowledgeable in anatomy and kinesiology (specifically referring to muscle attachments and joint movements) may have greater success in designing flexibility programs for their students.
Although stretching techniques are continually evolving, presently there are no universally agreed-upon guidelines to follow for prescribing the type, duration and number of repetitions of any given stretching technique. It is certain that for flexibility to increase, careful application of a slow stretch just past the point of limitation is necessary. Depending on a client's fitness level, goals, limiting factors of flexibility, and other exercise program participation, an individualized flexibility program can be designed using the following guidelines:
1) Assess your client's flexibility in order to pinpoint strengths and weaknesses.
2) Design a program that stretches the specific muscles used by the client during physical activity or sport participation.
3) Warm-up before stretching to increase the body temperature and range of motion.
4) Perform stretching exercises daily.
5) Stretch all major muscle groups, as well as opposing muscle groups.
6) Focus on the muscles involved in the stretch, minimizing the movement of other body parts.
7) Hold stretches between 15 and 30 seconds. Recent research suggests that four sets of 15 to 20 seconds per stretch will result in optimal gains.(7)
8) Stretch to the limit of movement, not to the point of pain. This is referred to as the "endpoint" of the stretch.
9) Keep the breathing slow and rhythmical while holding the stretches.
10) Stretch the muscles in various positions, as stretching in different planes may enhance muscle relaxation and improve overall range of motion at the joint.
11) Attempt to relax the target muscle before going into the stretch.
12) Stretch after each vigorous workout to reduce the potential of delayed-onset muscle soreness and to encourage mind and body relaxation.
13) If the stretch yields pain in the joint area, back off the movement and make sure the stretching technique is correct. It may be necessary to try another position or another stretch for the target muscles.
Flexibility training should be a fundamental part of any exercise prescription. It is best to include a variety of stretching methods (e.g., static and PNF techniques) and stretches depending on the knowledge/experience of the trainer and the needs of his/her clients. Emphasis should be placed on proper body position, form and execution of each stretch. When done correctly and regularly, stretching can be very enjoyable and relaxing. With so much attention now being directed toward designing programs that enhance the interaction of mind, body and spirit, it is certain that flexibility training will become an integral part of the individual's total exercise program.
Stretching exercise descriptions
1. Deltoid (posterior), upper trapezius, rhomboid stretch. Pull the elbow across the chest toward the opposite shoulder.
2. Pectorals, anterior deltoid, and biceps stretch (with short towel or rope). Clasp a towel about shoulder width or use your hands if there is no towel. Lift arms up and away from the body.
3. Adductor stretch. Keep a normal lumbar curve by sitting up tall. Pull the feet comfortably toward body. Allow knees to go toward floor to stretch adductors of both legs.
4. Spinal, gluteal, abductor and neck stretch. Keep normal lumbar curve by sitting up tall. Use the arm and elbow to keep bent leg stationary during the rotational stretch. Do not lock the elbow joint of the supporting arm.
5. Lumbar and hip extensor stretch. Grab behind thighs, keeping head on floor. Lift the buttocks slightly off the floor to facilitate a lumbar stretch. To add the hamstrings to this stretch, extend both legs, keeping a slight bend in the knees.
6. Hip flexor and quadriceps stretch. Grasp the ankle of the top leg and bring the leg back to stretch hip flexors. Bring the heel towards the buttocks for the quadriceps stretch. Note how the bottom leg is bent, with slight flexion at the hip to take stress off the back. Also note how model is resting head on floor for support.
7. Seated gastrocnemius stretch. Sit upright with one leg extended forward and the other leg flexed at the knee. Place the towel around the forefoot of the extended leg. Pull the foot toward the body, dorsiflexing the ankle, to stretch the gastrocnemius and soleus.
8. Prone stretch. Lie in a prone position with the body extended and the legs spread shoulder width. Clasp the hands together and keep the elbows on the floor. Lift the head and trunk, stretching the abdominals and hip flexors.
Example of contract-relax agonist contract stretch
Step 1: Bring both legs toward the chest until tension is felt in hamstrings (note slight bend in legs to lessen stress at knees).
Step 2: While resisting with hands and arms, try to extend legs (attempting to bring legs toward floor). This is the contract phase.
Step 3: Relax hamstring contraction (relax phase) and place hands between the knees and hips, just above knees; in this position, attempt to bring legs into chest by contracting hip flexors; resist any movement of the legs with the arms (agonist contract phase).
Step 4: Relax hip flexor contraction and bring legs toward the chest to a new point of limitation.
Johns, R. J., & V. Wright. Relative importance of various tissues in joint stiffness. Journal of Applied Physiology, 17, 824-828, 1962.
Anderson, B., & E.R. Burke. Scientific, medical, and practical aspects of stretching. Clinics in Sports Medicine, 10, 63-86, 1991.
Holland, G. J. The physiology of flexibility: A review of the literature. Kinesiology Review, 49-62, 1968.
Sapega, A. A., T.C. Quendenfild, R.A. Moyer, & R.A. Butler. Biophysical factors in range-of-motion exercises. The Physician and Sportsmedicine, 9, 57-65, 1981.
Fleck, S. J., & W.J. Kraemer. Designing resistance training programs. Champaign, IL: Human Kinetics Publishers, 1987.
Safran, M. R., W.E. Garrett, A.V. Seaber, R.R. Glisson & B.M. Ribbeck. The role of warmup in muscular injury prevention. The American Journal of Sports Medicine, 16, 123-129, 1988.
Taylor, D., J.D. Dalton, A.V. Seaber., & W.E. Garrett. Viscoelastic properties of muscle tendon units -- the biomechanical effects of stretching. American Journal of Sports Medicine, 18, 300-309, 1990.
Holt, L. E., T.M. Travis., & T. Okita. Comparative study of three stretching techniques. Perceptual and Motor Skills, 31, 611-616, 1970.
Etnyre, B. R., & A.D. Lawrence. Antagonist muscle activity during stretching: a paradox re-assessed. Medicine and Science in Sports and Exercise, 20, 285-289, 1988.
Sullivan, M. G., J.J. Dejulia, & T.W. Worrell. Effect of pelvic position and stretching method on hamstring muscle flexibility. Medicine and Science in Sports and Exercise, 24, 1383-1389, 1992.
Kraus, H., & R.P. Hirschland. Minimum Muscular-Fitness Test in School Children. Research Quarterly, 25, 178-188, 1954.
Len Kravitz, Ph.D., has a doctorate in health promotion and exercise science . He is an adjunct professor of exercise science at the University of New Mexico, author of three books and producer of four exercise videos. Vivian H. Heyward, Ph.D., is a professor of exercise science at the University of New Mexico. She is the author of Advanced Fitness Assessment & Exercise Prescription (Human Kinetic Publishers) and a certified ACSM health/fitness instructor.