Isotonic And Plyometric Exercises
These terms combine the prefix “iso” (meaning “same”) with “tonic” (strength) and “plio” (more) with “metric” (distance). In “isotonic” exercises the force applied to the muscle does not change (while the length of the muscle decreases or increases) while in “plyometric” exercises the length of the muscle stretches and contracts rapidly to increase the power output of a muscle.
Weight training is primarily an isotonic form of exercise, as the force produced by the muscle to push or pull weighted objects should not change (though in practice the force produced does decrease as muscles fatigue). Any object can be used for weight training, but dumbbells, barbells, and other specialised equipment are normally used because they can be adjusted to specific weights and are easily gripped. Many exercises are not strictly isotonic because the force on the muscle varies as the joint moves through its range of motion. Movements can become easier or harder depending on the angle of muscular force relative to gravity; for example, a standard biceps curl becomes easier as the hand approaches the shoulder as more of the load is taken by the structure of the elbow. Certain machines such as the Nautilus involve special adaptations to keep resistance constant irrespective of the joint angle.
Plyometrics exploit the stretch-shortening cycle of muscles to enhance the myotatic (stretch) reflex. This involves rapid alternation of lengthening and shortening of muscle fibers against resistance. The resistance involved is often a weighted object such as a medicine ball or sandbag, but can also be the body itself as in jumping exercises or the body with a weight vest that allows movement with resistance. Plyometrics is used to develop explosive speed, and focuses on maximal power instead of maximal strength by compressing the force of muscular contraction into as short a period as possible, and may be used to improve the effectiveness of a boxer’s punch, or to increase the vertical jumping ability of a basketball player. Care must be taken when performing plyometric exercises because they inflict greater stress upon the involved joints and tendons than other forms of exercise.