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Muscles
Muscles allow us to perform movement. Muscles are also responsible for posture and heat production (Thibodeau, Gary A. and Patton, Kevin T., Structure and Function of the Body, 11th Ed. Mosby Inc. 2000 Pg. 137). With bones acting as levers, muscles are the pulleys. The ability for muscles to contract and relax allows our bodies to breathe, produce a heart rate, and to move in many different directions. With over 600 muscles in the body, there are so many opportunities for various types of movement.
Some examples of movement (aka muscle actions) include flexion, extension, rotation, supination, pronation, inversion, eversion, plantar flexion, dorsiflexion, adduction, and abduction (to see brief definitions of all of these muscle actions, Visit my Muscle Action Descriptions page.
| Contraction | Description |
|---|---|
| Twitch | A brief contraction of all the muscle fibers in a motor unit (motor neuron and the muscle fibers it stimulates) in response to a single motor unit action potential (the ability for motor neuron to stimulate its associated muscle fibers). It is a rapid, jerky response |
| Tetanus | A rapid succession of separate twitches due to summation (two separate stimuli to the same motor unit causing a stronger contraction) |
| Isometric | Muscle length remains constant and tension changes |
| Isotonic | Tension remains constant, while muscle length changes (lifting weights) (Thibodeau, Gary A. & Patton, Kevin T., Structure and Function of the Body, 11th Ed. Mosby Inc. 2000 pg 140 |
| Isotonic Contraction | Description |
|---|---|
| Concentric | The muscle shortens during contraction (i.e. biceps when raising the arm during a bicep curl exercise) |
| Eccentric | The muscle lengthens during contraction (i.e. triceps when lowering the arms during a bicep curl exercise) |
