Muscle Contraction and Gravity
Muscle Contraction and Gravity
There are three types of muscle contraction:
● Concentric - isotonic
● Eccentric - isotonic
● Isometric
Concentric - the muscle increases in tension as the length of the muscle decreases
● Concentric contractions are shortening contractions
● Concentric contractions perform the function of the muscle or are agonist/assisting
Eccentric - as the muscle lengthens it allows the motion to occur by successively relaxing groups
of muscle fibers
● A lengthening contraction
● Performed by the antagonist of the muscle producing the movement
● Acts to slow the motion but is not relaxing
Isometric - when a muscle contracts against a weight which it cannot move or lift
● The tension or tone in its fibers increases but the muscle length remains the same
● Little or no visible movement occurs at the joint involved
Isotonic - contraction with movement at joint but tone remains relatively same. Tension changes
at different points in the joint range
Iso = same
Tonic = tone
Concentric and eccentric work together with normal movement along with stabilizers to produce
smooth controlled motion
Role of Gravity in Muscle Function
Gravity is one of the major forces the muscles must react to during joint motion. The role of
gravity changes depending on the position of the body and/or body part involved, the motion
being performed and the muscle being evaluated.
Anti-gravity (gravity resisted or AG) exercises
● Body part is lifted against the force of gravity
● A type of resistive exercise
Example: in the erect position elbow flexion is an anti-gravity motion so the muscle performing
that motion (biceps) is performing an anti-gravity contraction by lifting the forearm and hand
against gravity
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Muscle Contraction and Gravity
Gravity-assisted (GA) exercises
● Movement of a body part is assisted or helped by gravity
● Less work is required by the muscle since gravity is helping
● Patient positioning will determine the assistance given the muscle
Example: in the erect position elbow extension is a gravity-assisted motion so the muscle
performing that motion (triceps) is assisted by gravity with little or no muscular work required by
that muscle
Gravity-eliminated (GE) exercises
Movement of a body part is neither hindered by or assisted by gravity
Gravity has no effect on the performance of the muscle
Most movements in the transverse plane are gravity-eliminated
Example: in the supine position hip abduction is a gravity-eliminated motion so that muscle
which performs hip abduction (gluteus medius) is neither helped nor resisted by gravity
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