Muscle Power
P= Wf-Wi/tf-ti = Fv *Power relates strength (force) to speed V(velocity)*
Power is the limiting factor in muscle performance. Muscle power exists in a balance because in a given muscle, increasing the velocity of a contraction decreases the force exerted. The maximum power is generally obtained at 1/3 the max force and 1/4 the max speed.
Muscle Endurance is the ability to maintain a force over a period of time.
(photo courtesy of startribune.com)
A single muscle contraction is called a twitch. If muscle is stimulated to twitch at faster and faster rates eventually a state is reached (maximum power) where muscle can not contract and relax any faster and remains contracted. This state is tetanus.