One definition of flexibility is the absolute range of movement in a joint or series of joints that is attainable in a momentary effort. This definition indicates that flexibility is not a general attribute, but rather is specific to a particular joint or set of joints. It is incorrect to assume that an athlete is innately flexible throughout this entire body; being flexible in one particular joint does not imply being flexible in another.
Stretching does significantly more than just increase flexibility. Benefits of stretching include: enhanced ability to learn and perform skilled movements; reduced risk of injury to joints, muscles, and tendons; increased mental and physical relaxation; enhanced sense of body awareness; reduced muscular soreness; reduced muscular tension; and increased suppleness by stimulating the production of chemicals that lubricate connective tissues. BMTs’ expertly designed flexibility protocols are one of the keys to enabling a world-class athlete to compete injury-free well into his 40’s.
Flexibility can be categorized according to whether it involves motion (dynamic) or is stationary (static). Dynamic flexibility is the ability to perform active movements of the muscles to bring a limb through its full range of motion in the joints. Static-active flexibility is the ability to assume and maintain extended positions using only the tension of the agonists and synergists while the antagonists are being stretched. Static-passive flexibility is the ability to assume extended positions and then maintain them using only body weight (gravity), the support of the limbs, or some other apparatus (such as a ballet barre); the flexibility to maintain the position is not generated exclusively from the muscles, as it is with static-active flexibility. Research has shown that active flexibility more closely simulates and prepares for sports movements than does passive flexibility. Active flexibility is harder to develop than passive flexibility; not only does active flexibility require passive flexibility in order to assume an initial extended position, but it also requires muscle strength to hold and maintain that position.
Flexibility is affected by the following factors: 1) the type of joint (many joints are not intended to be flexible); 2) the internal resistance within a joint; 3) bony structures which limit movement; 4) the elasticity of muscle tissue (muscle tissue that underwent fibrosis due to a previous injury has minimal elasticity); 5) the elasticity of tendons and ligaments (ligaments have minimal stretch and tendons should not stretch); 6) the elasticity of skin (skin has minimal degree of elasticity); 7) the ability of a muscle to relax and contract to achieve the greatest range of movement; 8) the temperature of the joint and associated tissues (joints and muscles have increased flexibility at body temperatures that are elevated 1 to 2 °F).
The most important factors influencing flexibility are bone structure, muscle mass, excess fatty tissue, and connective tissue. Depending on the type of joint, the bone structure places significant limits on flexibility. This is a manner in which age can be a factor limiting flexibility, since older joints tend to have weakened integrity compared to younger ones. Muscle mass can be a limiting factor when the muscle is so hypertrophied that it interferes with the ability to take the adjacent joints through their complete range of motion.
Each type of tissue plays a certain role in joint stiffness: The joint capsule (a saclike structure that encloses the ends of bones) and ligaments are the most important factors, accounting for 47% of the stiffness, followed by the muscle's fascia (41%), the tendons (10%), and skin (2%). Our efforts to increase flexibility are directed at the muscle's fascia, however. The rationale for this is that muscle fascia is composed of a higher quantity of elastic tissue, whereas ligaments and tendons (which have less elastic tissue) are not intended to be stretched far. Overstretching them may weaken the joint's integrity and cause destabilization, which increases the risk of injury.
It is a common misconception that there must always be a trade-off between flexibility and strength. Our strength and power protocols integrate movements that demand a high degree of flexibility, so that the athlete learns to coordinate both attributes. In fact, flexibility training and strength training can enhance one another, as evidenced by the range of motion our Olympic weightlifters exhibit.
When stretching is performed incorrectly, the athlete does not attain all of the benefits and risks injury. Common mistakes that our stretching protocols eliminate include: improper warm-up; inadequate rest between sessions; overstretching (it is possible for the muscles of a joint to become too flexible); performing the wrong exercises; and performing exercises in the wrong or sub-optimal sequence.