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Types of exercises
Isotonic, isometric and plyometric exercises
These terms combine the prefix "iso" (meaning "same") with "tonic" (strength)
and "metric" (distance). In "isotonic" exercises the force applied to the muscle
does not change, and in "isometric" exercises the length of the muscle does not
change.
Weight training is primarily an isotonic form of exercise, because the muscles
are used to push or pull weighted objects. 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.
However, some exercises are not strictly isotonic because the force on the
muscle varies as the joint moves through its range of motion, even though the
force of the exercise remains constant.
Some forms of weight training use isometric contractions to further stress the
muscles after or during a period of isotonic exercise. In this case the muscles
flex and hold a stationary position, and no movement of a load takes place.
Another form of training that often uses weights has a different goal.
Plyometric exercises 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 a resistance. The resistance involved is
often a weighted object such as a medicine ball, but can also be the body itself
as in jumping exercises. Plyometrics is used to develop explosive speed, and
focuses on power instead of maximal strength, and may be used to improve the
effectiveness of a boxer's punch, for example, or to increase the vertical
jumping ability of a basketball player.
Isolation exercises versus compound exercises
The leg extension is an isolation exercise.An isolation exercise is one where
the movement is restricted to one joint. For example, the leg extension is an
isolation exercise for the quadriceps. The other muscle groups are only
minimally involved—they just help the individual maintain a stable posture—and
movement occurs only around the knee joint. Other examples are the
straight-legged deadlift (hip extension) and the dumbbell/barbell curl (elbow
flexion).
Compound exercises work several muscle groups at once, and include movement
around two or more joints. For example, in the leg press movement occurs around
the hip, knee and ankle joints. This exercise is primarily used to develop the
quadriceps, but it also involves the hamstrings, glutes and calves.
Compound exercises are generally similar to the ways that people naturally push,
pull and lift objects, whereas isolation exercises often feel a little
unnatural.
The leg press is a compound exercise.Each type of exercise has its uses.
Compound exercises build the basic strength that is needed to perform everyday
pushing, pulling and lifting activities. Isolation exercises are useful for
"rounding out" a routine, by directly exercising muscle groups that cannot be
fully exercised in the compound exercises.
The type of exercise performed also depends on the individual's goals. Those who
seek to increase their performance in sports would focus mostly on compound
exercises, with isolation exercises being used to strengthen just those muscles
that are holding the athlete back. Similarly, a powerlifter would focus on the
specific compound exercises that are performed at powerlifting competitions.
However, those who seek to improve the look of their body without necessarily
maximizing their strength gains (including bodybuilders) would put more of an
emphasis on isolation exercises.
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