Pranayama, or breath control, is the fourth limb in a yogi's path toward samadhi . One of the most important yogic practices, it helps the yogi gain control over the movement of prana (life energy) throughout the body. But whether viewed through esoteric yoga physiology or the scientific physiology of the West, the connection between relaxation, stretching, and breathing is well established. Physiologists describe this mechanical and neurological correlation of movement and breath as an instance of synkinesis , the involuntary movement of one part of the body that occurs with the movement of another part.
Concentric muscle contractions occur when a muscle shortens during contraction, as in the upward motion when performing a biceps curl. An eccentric contraction occurs when a muscle lengthens with contraction, as in the "negative" or lowering motion of a biceps curl. An example of an isometric (muscle contracts while maintaining constant length) contraction would be pushing against an immovable object. An example of an isokinetic (muscle has constant speed of contraction) occurs with specialized equipment like Cybex machines. Plyometric contractions occur when a muscle rapidly lengthens just prior to contraction - like during repetitive box jumping.
Woo and Buckwalter describe the mechanisms, barriers, and molecular processes involved in ligament and tendon injury and repair.