Proper execution of any strength exercise is important to decrease the risk of injury. Seemingly small changes in technique can alter the effectiveness and purpose of an exercise. Although the basic execution is the same for the chest and triceps dip, the body position is slightly different, which changes the target muscles.
For both exercises, you suspend your body between dip bars with your arms fully extended. Elbows are bent, pointing directly behind you, to lower your body toward the floor. The movement stops when your elbows are at a 90-degree angle. The exercise concludes as you press back up. What differentiates the triceps dip from the chest dip is the angle of the body. For the triceps dip, maintain a vertical body position throughout the exercise, but for the chest dip, lean forward about 30 degrees.
The triceps dip targets the triceps, a group of three muscle heads on the back of the upper arm, which are responsible for straightening the elbows. The chest muscles assist during the exercise. Leaning forward during the dip exercise shifts the emphasis to the chest muscles, making them the primary movers and the triceps the secondary movers. The front shoulders assist in both versions of the dip exercise.
Parallel dip bars offer only one grip width, but some dip bars offer different grip options. Non-parallel dip bars widen at one end and other bars flip out, offering a narrow and wide grip. Shift the muscle emphasis of the dip exercise by changing your grip. A wide grip -- past shoulder-width -- emphasizes the chest, while a closer grip emphasizes the triceps. Your grip should not exceed the width of your elbows when they are at a 90-degree bend as this decreases the range of motion and the effectiveness of the exercise.
The dip exercises places the shoulder joints in a precarious, unsupported position with a high load. This biomechanically disadvantageous position increases the risk of shoulder injury. To reduce your risk, limit the range of motion; do not lower your torso past a 90-degree bend in the elbows. If you have shoulder problems, choose an alternative exercise.