Force of Muscle Contraction

The force that a muscle produces is controlled by four things:
(1) the number of muscle fibers stimulated
(2) the size of the muscle fibers
(3) the frequency of stimulation
(4) and the degree of muscle stretch.

The Number of Muscle Fibers Stimulated

The number of muscle fibers stimulated affects the amount of force that a muscle produces. Muscle fibers, motor units, are recruited; the more recruited, the greater the force.

The Size of Muscle Fibers

Different sized muscle fibers result in varying amounts of force produced. The larger the muscle fiber which is stimulated the greater the force. Larger, bulkier muscles require bigger muscle fibers to produce the amount of force in which the muscle requires for movement.

The Frequency a Muscle Fiber is Stimulated

Muscle fibers react to the frequency of stimuli. More frequent stimuli result in a greater amount of force produced. When a muscle fiber is stimulated in quick succession it is not given the chance to relax. Thus, each subsequent muscle twitch is greater in force than the previous one.
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The Degree of Muscle Stretch

The degree a muscle is stretched affects the amount of force it can produce. When muscle fibers are stretched too far, that the filaments do not overlap, weak force is produced because tension cannot be produced because the myosin heads have nothing to attach to. Also, if the muscle fibers are compressed in too much force will be weak. The myofilaments, Z-discs, and filaments hinder one another and the fibers can not compress any farther to produce a contraction. The ideal length tension relationship results in maximum force. This is characterized by a slightly stretched muscle in which the thick and thin filaments overlap, permitting an optimal muscle contraction.