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As the name implies, a
single-joint movement involves motion at only one joint. A good example
is the preacher curl workout. When performed correctly, this
bodybuilding exercise isolates
the biceps by anchoring the entire body, allowing movement at only the
elbow joint. A single-joint movement can be thought of as an isolation
movement. Such movements typically concentrate on one particular muscle
or muscle group and are frequently used for enhancing definition and
developing striations.
Multiple-joint
movements, as you may have guessed, involve motion of more than one
joint and more than one muscle group. Multi joint movements are
considered the "mass builders" in bodybuilding because they usually involve larger muscle
groups and using heavier weights during the bodybuilding workout session.
The squat
workout is a classic
example. Motion at 3 joints is required to execute this exercise
properly. Muscles of the hamstrings, buttocks and lower back contract to
extend the hip joint as the weight is raised from the squatting position
to standing upright. Simultaneously, the quadriceps contract to
extend the knee joint and straighten the legs, and the calves are
involved in extension of the ankle joint (plantar flexion). With all
this muscle activation happening at once, you can understand why doing
heavy squats makes you feel like you've been run over by a bus.
When considering the
joint movement(s) of a given exercise, keep in mind that performing
single-joint movements becomes increasingly difficult as the target
muscle group nears the torso. Distal muscle groups (biceps, triceps,
calves, etc) are easier to isolate than proximal ones, such as those of
the chest or back.
Exercises for the
chest muscle, with certain exceptions, are predominantly multi joint movements.
Most are pressing movements, requiring extensions of the elbow and
contraction of the triceps. Single joint movements of the back,
especially the latissimus dorsi, are even rarer. Contraction of the
latissimus dorsi relies primarily on pulling movements. As you pull the
weight closer to the body; the biceps muscle contract to bend the elbow.
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