Isolate your lats with wide grip chin-ups

Isolate your lats with wide grip chin-ups

The biceps assist in just about every back exercise. While your latissimus dorsi pull your arms to your body, your biceps bend your arms at the elbow. Sometimes, especially when first starting, it can be difficult to get a good back workout because your biceps, being a small muscle group, will give out before your back does.

If you have the upper-body strength, try using a wide grip for your chin-ups to target your lats. Grip the bar as wide as necessary so that when your arms are bent at 90 degree angles they are out at your sides, not in front of you. This usually equals out to twice shoulder width. By widening your grip, you allow your arms to travel only in the frontal plane. This minimizes bicep involvement by reducing the amount the biceps must contract before the lats are fully contracted.

There is nothing wrong with allowing your biceps to assist the movement, especially once your lats are tired out and need some help. After my sets of wide grip chin-ups with a pronated hand position (meaning my hands, when above my head, are facing forward), I always switch to a narrow, hands-supinated grip (hands facing back towards me) to get an extra set or two I otherwise couldn't. By mixing up something as simple as the width of your grip and the direction of your hands, you can hit muscles from different angles and get a more intense workout.

Note: Some people make a distinction between chin-ups and pull-ups, but most don't. They are usually interchangeable.
--------------------------------

Extensive bodybuilding.com article on pull-ups
Grass Roots Project article on the importance of bodyweight exercise