Phil Heath's Workout Tips - Exercise 3 - Machine Tricep Dips: Another great exercise for the triceps, using the machine helps to focus lots of attention on all heads of the triceps. To begin the exercise, push down and stretch before holding for one count at the bottom of the movement, squeezing the muscle as you do so before slowly letting the weight come back up. As this exercise is a compound movement, avoid the use of momentum or hunching over as this begins to bring in more of the chest. Aim for 3-4 sets of 15 reps with 60-90 seconds rest in between sets.
For smaller muscle groups such as the triceps, aim for higher rep ranges to avoid putting excess strain on the joints. Phil Heath - Mr Olympia & Nick Jones - World Bodybuilding Champion