Focus on using your lats to move the weight rather than your biceps. Your forearms should only serve to hold the weight, not move the weight.
Squeeze your lats in at the bottom of the exercise and pause for a count of 1-2 to get the most out of this exercise.
Instructions
Set up for the reverse grip lat pull down by attaching a wide grip bar to the machine, selecting the weight you want to use and adjusting the thigh pad.
While standing, grasp the bar with an underhand grip (palms facing up) at wider than shoulder width apart.
Holding the bar, sit down on the machine. This should take the weight off the stack.
Keeping your back straight, eyes facing forward, and without leaning back, slowly pull the bar down to your upper chest. Do not let the bar touch your chest.
Pause, and then slowly lower the weight back to the starting position. Do not let the weight touch the stack.