Control of Muscle Tension
1. describe the different types of muscle contractions
2. explain the mechanics of muscle contraction
3. identify and explain the factors contributing to muscle tension
The skeleton is a lever and fulcrum system. The contraction of the muscle is the effort.
The fulcrum is the joint and the load is the weight of another body part.
Types of muscle contractions:
There are concentric isotonic, eccentric isotonic and isometric muscle contractions. With
concentric isotonic contractions, the muscle shortens in length and the joint angle
decreases (picking a book up). During eccentric isotonic muscle contraction the muscle
length lengthens (lowering a book down). Finally with isometric contractions the muscle
length does not change (holding a book straight out).
The velocity of muscle contraction is inversely proportional to the load. This implies that
a large force cannot be exerted in a very rapid movement (as in powerlifting), that the
greatest velocities are attained under conditions of low loading, and that the intermediate
values of force and velocity depend on the maximal isometric force.
Each muscle fiber is innervated by one motor neuron. All nerve impulses are identical.
The force of muscle fiber contraction does vary; a muscle fiber is capable of producing a
much greater force than the one that results from a single action potential. The total force
of tension that a single muscle cell can produce depends mainly on the rate at which
nerve impulses arrive at the neuromuscular junction (frequency of stimulation).
Maximum tension is also affected by the amount of stretch before contraction and by
nutrient (calcium) and oxygen availability. The total tension a whole muscle can produce
depends on the number of muscle fibers that are contracting in unison (number of cross
• The length tension relationship states that, the forcefulness of muscle contraction
depends on the length of the sarcomeres within a muscle during contraction.
Maximum tension occurs when the resting sarcomere length is 2.02.4nano m. A
muscle fiber develops its greatest tension when there is an optimal zone of
overlap between thick and thin filaments.
• Motor Units. Even though each skeletal muscle fiber has only a si