Your muscles respond in different ways to specific forms of exercise. Changing the amount of tension applied to the muscle, the speed of the movement or the exercise range of motion can develop muscle strength, power or size. Isometric movements can be used to sustain strength or develop power while isotonic movements, like weight training, can improve muscle strength and definition.
Isometric Exercise
Dr. Edward Laskowski of the Mayo Clinic notes muscles do not change length during isometric movements. These exercises are not effective at building muscle strength since the participant is not moving his muscles against tension through a range of motion. Since isometric movements help maintain strength and do not involve joint movement, individuals requiring rehabilitation might perform these exercises to avoid painful movements.
Isotonic
Isotonic exercises cause muscles to change length while contracting, causing movement of a body part. The two categories of isotonic contraction are concentric and eccentric movements. The concentric portion of an exercise causes the muscles to shorten while contracting. Eccentric movements involve the muscle lengthening upon being contracted.
Examples
Examples of isometric movements involve gripping a baseball bat or tennis racket. Your muscles contract to stabilize the bat or racket yet there is no movement in the joints of the hand or change in length of the contracting muscle. An example of an isotonic concentric movement is bending your elbow during a biceps curl, fully extending your arm and the biceps muscles. One example of an eccentric movement is kicking a football, where the hamstrings muscle lengthens to counterbalance the concentric contraction in the quadriceps muscle.
Considerations
Individuals with high blood pressure should avoid isometric exercises as the movements can cause a dangerous spike in blood pressure. Eccentric contractions place great tension on muscles and are commonly involved in sports-related injuries. Before starting an isometric or isotonic exercise regimen consult your physician.
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