Tarzan pull-ups are very similar to close-grip pull-ups in that the hands are placed very close to each other on the bar. However, instead of both palms facing away or towards the body, in a Tarzan pull-up, both palms face opposite directions.
Stand under the bar and grip it with the palm facing towards the body. Then, place the other hand at the base of the hand already on the bar with the palm facing away from the body (similar to how a baseball bat would be gripped). As with any other pull-up variation, arms will start at full extension, and you must tighten your core.
From this bottom position, pull upwards towards one side of the bar until the bar touches the trapezius (between the shoulder and neck), maintaining a neutral spine.
Lower your body until the arms are fully extended again. At this point, the movement can be repeated, pulling to the same side of the bar. You can also pull towards the other side of the bar and alternate.
The Tarzan pull-up is unique in that depending on which hand is closer to the body and which side of the bar the pull-up is performed on, the stimulus provided will differ. Like the close-grip pull-up, the latissimus dorsi and rhomboids will play a significant role with the Tarzan pull-up.
One advantage of this variation is the use of the neutral grip position. It eases tension on the forearm muscles and is excellent for those who may experience wrist pain.
While full ROM is vital for all pull-up variations, with the Tarzan pull-up, partial ROM really defeats the purpose of the movement. So it is important to allow full extension of the arms at the bottom of the movement and to pull up until the bar touches the trapezius.