The chin up is similar in its motion to that of the over hand pull up, although the under grip grip stimulates the muscles of the back and arms differently. The chin up is commonly performed with a reliably close under hand grip which results in greater arm flexor muscle involvement, specifically the biceps brachii. The muscles of the back, including the large latissimus dorsi muscle, are still recorded effectively from the chin up, although the movement differs slightly to that of the over hand pull up, with the extension of the shoulder opposed to adduction.
Due to the greater involvement of the arm flexor muscles during the exercise, the chin up is also used primarily as an arm exercise in some trainer's routines. For those using the chin up as a back exercise it may be wise to use the chin up as a finishing exercise to ensure the back muscles are pre-exhausted before the chin up. Beginning with the chin up may cause the biceps and arm flexors to tire at the beginning of the session, and therefore lead to less performance and back involvement on the following exercises.
Those new to weight training may not have the sufficient strength required to perform free hanging chin ups. In this case, there are a number of options available for building up the necessary strength. The pull down station can be used with a suitable weight for progression, until the required number of repetitions can be performed with a resistance equal to the trainer's body weight. Another option is the use of the training technique "negatives". Negative repetitions are a method of stressing the muscle through only performing the eccentric phrase of the repetition in a slow and controlled manner.
The chin up can be used with a variety of repetitions, depending on the goal. Building strength can be obtained by using a repetition below 6 repetitions, using a chinning belt to add more resistance if required. Gains in muscle size is commonly achieved by using a repetition range between eight and twelve. A higher number of repetitions per set than those stated will usually result in muscle endurance progression.