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.