There are two types of flexibility:

• Static flexibility is the ability to hold an extended position at one end or point in a joint’s range of motion. For example, static flexibility determines how far you can extend your arm across the front of your body or out to the side. Static flexibility depends on

Joint capsules Semielastic structures, composed primarily of connective tissue, that surround major joints.


Soft tissues Tissues of the human body that include skin, fat, linings of internal organs and blood vessels, connective tissues, tendons, ligaments, muscles, and nerves.

Collagen White fibers that provide structure and support in connective tissue.

Elastin Yellow fibers that make connective tissue flexible.

Elastic elongation Temporary change in the length of muscles, tendons, and supporting connective tissues.

Plastic elongation Long-term change in the length of muscles, tendons, and supporting connective tissues.

Proprioceptor A nerve that sends information about the muscular and skeletal systems to the nervous system.

Answers (Test Your Knowledge)

1. c. It’s best to do stretching exercises when your muscles are warm. Intensely stretching muscles before exercise may temporarily reduce their explosive strength and interfere with neuromuscular control.

False. Prolonged bed rest may actually worsen back pain. Limit bed rest to a day or less, treat pain and inflammation with cold and then heat, and begin moderate physical activity as soon as possible.

True. “Bouncing” during stretching can damage your muscles. This type of stretching, called ballistic stretching, should be used only by well-conditioned athletes for specific purposes. A person of average fitness should stretch slowly, holding each stretch for 10-30 seconds.

The flexibility of a joint is affected by its structure, by muscle elasticity and length, and by nervous system regulation. Joint structure can’t be changed, but other factors, such as the length of resting muscle fibers, can be changed through exercise; these factors should be the focus of a program to develop flexibility.

Joint Structure

How flexible a joint is depends partly on the nature and structure of the joint (Figure 5.1). Hinge joints such as those in your fingers and knees allow only limited forward and backward movement; they lock when fully extended. Ball-and-socket joints like the hip enable movement in many different directions and provide for a greater range of motion. Joint capsules, semielastic structures that give joints strength and stability but limit movement, surround the major joints. The bone surfaces within the joint are lined with cartilage and separated by a joint cavity containing synovial fluid, which cushions the bones and reduces friction as the joint moves. Ligaments, both inside and outside the joint capsule, strengthen and reinforce the joint. For an illustration of the knee joint and more about its function, see page T4-5 of the color transparency insert “Touring the Musculoskeletal System,” in Post 4. range of motion The full motion possible in a joint. TERMS

Heredity plays a part in joint structure and flexibility. For example, although everyone has a broad range of motion in the hip joint, not everyone can do a split. Gender may also play a role. Some studies have found that women have greater flexibility in certain joints.

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