There are two general types of weight-training exercises.
COMPOUND movements involve two or more joints, and therefore two
or more muscles. ISOLATION movements use only one joint and
therefore only one muscle (or one muscle group). If you
weight-train regularly, you probably do both kinds of exercises.
Each type has its own advantages:

- COMPOUND MOVEMENTS are often considered more " efficient"
because they work several muscles at the same time. These
exercises strengthen the smaller, supporting muscles in addition
to the larger targeted muscles. Examples of compound exercises:
Bench press (uses shoulder and elbow joints) squats (hip and
knee joints).

-ISOLATION MOVEMENTS are good for sculpting, or defining, a
specific muscle you wish to tone. These exercises may also be
better for areas where the tendons have been injured. Examples of
isolation exercises: Reverse flye (shoulder joints) leg
extension (knee joint).