Flexibility for Fitness
Trainers in health clubs spend a great deal of time teaching clients about cardio and strength training. What may be lacking in these exercise programs is flexibility training. Flexibility can be defined as the ability of a joint to move through an optimum range of motion (ROM). Not only do flexibility exercises such as stretching help combat stiff muscles and joints, they also help to increase ROM.2,14,19 Stretching is especially important with high-intensity exercise or when repetitious movements are used during the activity. When the same muscles are used over and over again, such as with running, cycling and swimming, they gradually become stiffer. The increased tightness could result in a possible injury to muscles, tendons and ligaments. Many injuries can occur from a lack of proper stretching, and incorporating stretch training into your clients' exercise programs can help them improve their overall levels of fitness.
When to stretch
All of the muscle groups that are going to be used in a workout should be stretched prior to the exercise, following a thorough warm-up to slightly increase muscle temperature. Stretching can also be done after the workout. This will help prevent muscular soreness in the days after exercise. In addition to stretching prior to exercise, specific training to improve ROM should be performed at least three times per week.
Benefits of flexibility
Maintaining flexibility becomes even more important as people age. It can improve the quality of life by allowing people to perform what once were simple daily tasks, such as tying their shoes or reaching to the top shelf of a cabinet. Other benefits of flexibility include a reduced risk of injury to muscles and joints, increased body awareness and balance, better posture, improved coordination and enhanced performance of skilled movements.1,6,7,15,18
As with many types of exercise, there are some contraindications to stretching, including a bone blocking the motion, a recently fractured bone, an inflamed or swollen joint, osteoporosis, sharp pain when stretching, a recent sprain or strain, or a vascular disease, such as a blood clot.
Factors that influence flexibility
Some of the main factors influencing flexibility include the following:
Joint structure. The type of joint determines the degree of ROM.11 For example, a balI-and-socket joint, like the shoulder, has a greater ROM than a hinge joint, like the wrist.
Age. With age, muscles go through a shortening process due to a lack of physical activity and a loss in elasticity in the connective tissues surrounding the muscles.16,20 As a result, there tends to be a decrease in flexibility with age.
Gender. Females tend to be more flexible than males of similar age throughout life, generally due to anatomical variations in joint structures.8,18
Exercise. Participation in regular exercise involving full ROM generally enhances flexibility, while a sedentary lifestyle often results in diminished flexibility.5
Temperature. An increase in either body temperature (as a result of exercise) or external temperature increases ROM.13,17
Pregnancy. During pregnancy, the pelvic joints and ligaments are relaxed and capable of a greater ROM.4
Types of stretching
There are three major types of stretching used to increase flexibility: static stretching, dynamic or ballistic stretching, and proprioceptive neuromuscular facilitation (PNF) stretching.
Static stretching. Static stretching involves holding a stretched position that passively places the muscles and connective tissues at their greatest possible length without pain for about 15 to 30 seconds. It is the most commonly used flexibility technique.
Many people tend to rush through their stretches so they can begin their workout, and, consequently, do not hold the stretches long enough. Holding a stretch for 15 seconds compared to 5 seconds has a greater effect on improving ROM, and holding a stretch for 30 seconds yields greater improvements in ROM than holding it for 15 seconds.2,14 However, this is where the relationship between the time spent holding a stretch and improvements in ROM ends. More is not always better. Increasing the stretching time to 60 seconds does not improve flexibility any more than holding a stretch for 30 seconds.2,3 For the frequency, when static stretching is performed three times per day, flexibility is not enhanced any more than when it is performed only once per day. This is good news for people who don't want to spend a lot of time stretching.
Ballistic stretching. Ballistic stretching uses repetitive bouncing movements of short duration, using momentum from a moving body or limb to forcibly increase the ROM. This type of stretching places an individual at a high risk for injury because of its stress on the muscles and connective tissues. Therefore, it is not usually recommended.
Proprioceptive neuromuscular facilitation (PNF) stretching. PNF stretching involves alternating muscle contractions and relaxation to improve the ROM. There are two kinds of PNF stretching: contract-relax and contract-relax agonist-contract. Using the contract-relax method, a targeted muscle group is first passively stretched, typically by a partner. Then the individual isometrically contracts (slightly less than maximum) the muscle group against a resistance (typically the partner) for a few seconds. Finally, the contracted muscle group is relaxed and then stretched to a new point of limitation. The sequence is usually repeated a few times. As long as the contraction phase is a few seconds (long enough to generate a significant amount of tension in the muscle), the exact time of holding the contraction does not seem to affect the increase in flexibility, with 10 seconds yielding no greater improvement in ROM than 6 seconds or even 3 seconds.12 Again, more is not always better.
The contract-relax agonist-contract method employs a contraction of the opposing muscle group following the stretch of the targeted muscle group. For example, if your clients want to improve the flexibility of their hamstrings, stretch the hamstrings to the point of limitation, then have your clients contract the hamstrings by pushing their legs against your resistance. Maintain the contraction for a few seconds and then relax. Finally, restretch the hamstrings to the point of limitation (which should be slightly further than the initial stretch). When using the contract-relax agonist-contract method, after the contract, relax and restretch phases, have your clients contract their quadriceps for a few seconds against a resistance. Relax the quadriceps and then restretch the hamstrings again to a new point of limitation.
Mechanism of stretching
There are two sensory organs within skeletal muscles that function as protective mechanisms against injury during passive and active stretching. The most abundant of these proprioceptors are the muscle spindles, which are located within the center of a muscle. In response to a stretch, the muscle spindle sends a message to the central nervous system. If the muscle is overstretched or stretched too fast, the central nervous system activates the motor neurons of the stretched muscle through a feedback loop, causing the muscle to contract. This sequence of events is called the stretch reflex. The other sensory organ, the Golgi tendon organ, is found at the musculotendon junction. When excessive force is generated in the muscle, the Golgi tendon organ triggers a reflex opposite that of the muscle spindle to inhibit muscle contraction and causes the muscle to relax. The Golgi tendon organ helps to prevent injury by preventing the muscle from developing too much force or tension during active stretching.
Understanding the role of the muscle spindle helps to shed light on why ballistic stretching increases the chance of injury. With a ballistic stretch, the muscle is stretched at a faster speed than during a static stretch. In response to the speed of stretch, the stretch reflex causes the muscle to contract. Therefore, stretching exercises with bouncing movements will repetitively call on the muscle spindle to initiate muscle contractions, developing tension in the muscle and increasing the chance of injury.
Similarly, the role of the Golgi tendon organ helps to explain why PNF stretching is so effective at increasing ROM. When the muscle is contracted after its initial stretch, the inverse stretch reflex causes it to relax. This relaxation helps to decrease any tension and allows for further stretch.
Specificity of flexibility
Flexibility does not exist as a general characteristic, but is rather specific to a particular joint and joint action. Just because individuals have a high ROM at one joint does not mean that they have a high ROM at other joints. How individuals use their joints will affect flexibility and ROM. For example, baseball pitchers will have a greater range of external rotation in the shoulder of their throwing arms than their other shoulder; hurdlers will have greater flexibility in the hamstrings of their lead legs compared to their trail legs; and right-handed people who perform many daily tasks with their right arms will typically have greater flexibility in their right-sided joints.
This specificity of flexibility is another example of how the body will adapt to the stresses placed on it. Therefore, to increase flexibility in the entire body, all of the muscles need to be stretched. Since a stretched muscle tends to return to its prestretched resting length, people with flexibility problems will continue to have problems unless they faithfully adhere to a regular stretching program. Long-term stretching increases ROM by increasing stretch tolerance rather than the passive properties of the muscle itself.9,10 It is a common belief that resistance training will decrease flexibility, but as long as the weight is moved throughout the full ROM with proper form, an individual can improve strength throughout the ROM without losing flexibility.19,20 FM
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Jason R. Karp has a master's degree in exercise physiology and biomechanics. He is the head track and field coach at George Washington High School in San Francisco, Calif., a professor in the fitness certificate program at the University of California at Berkeley, and the head marathon coach for San Francisco Fit. He is also a personal trainer, a freelance writer, a New Balance-sponsored coach and a competitive distance runner.
©Copyright 2006. Fitness Management
Article by Jason R. Karp, M.S