• actually carries out action
• causes movement of body part at joint when contracted
• can be several different muscles working together

 assists prime mover

resists the prime mover

as muscles can only pull, never push, there has to be a muscle that opposes the action of any given muscle.  So, muscles are sometimes found in pairs.

Static

Tension, but length remains same

Dynamic

Tension controls or creates joint movement

Muscle develops tension as it shortens

(contracts-contracted muscle, concentric m

movement)

ie.   rectus femoris is concentric during knee extension

Muscle lengthens under tension

(during elbow flexion, tricep is eccentric)

ie.  Soleus is is eccentric with ankle extension

Lever - rod, ie. bone

Resistance-wt to be moved, ie. barbell

Force-effort used to counter resistance

Axis (Fulcrum)-point at which lever moves, ie. joint

First Class Lever

Force and Resistance on opposite sides of Axis(fulcrum)

Force

Axis

Resist

ie. 

Applied force and resistance on same side of axis(fulcrum).  Resistance closer to Axis.

Force

Resistance

Axis(Fulcrum)

ie.