Pull-Up Bars

Doorway Pull-up Bars

You don't need expensive workout machines or weights to develop upper body strength and definition.  An inexpensive pull-up bar is all you need to strengthen and tone your back, arms, shoulders, chest, abs, and more.  Doorway pull-up bars are a great option because they offer portability, ease of setup, and don't require drilling or screws.
Maintaining proper form is the key to increasing strength when doing pull-ups.  The principle is to use your body's own resistance to create maximum impact where it counts: the pecs, biceps, abs, and obliques.  Pull-up bars are a recommended tool if you are following the P90X workout program.

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There are many variations to the traditional pull-up that can be used to target different muscles.  These variations often involve modifying your grip or hand placement.