Stand in front of the weight stack about a foot away from the cable apparatus. Grab the handle with your palm down (reverse grip) and tense the cable a bit so that you can lean back a touch. This is your starting position.
Curl the weight up until your forearm is almost completely vertical. Then, curl back down to the starting position but don't extended your arm completely straight to lockout. Always keep tension in your arm for optimal movement efficiency and muscle development.
Finally, repeat the entire movement for the desired or prescribed number of repetitions and then switch and do the same with your other forearm.
Perform this exercise in a smooth and fluid motion
Don't extended your arms completely on the downward portion of the movement
SPECIAL NOTES & LEVEL of DIFFICULTY VARIATIONS
To increase the level of difficulty, slow down the movement or increase the weight.
This exercise is ideal for beginners because it's fairly low impact on the wrists. The cable motion is smooth and guided making it very easy to get used to.
Once you do this exercise for a while you should be able to handle more advanced forearm exercises that involve the use of dumbbells. Until then, strengthen your forearms and grip by doing this exercise for at least 6 weeks.
Lastly, you will feel soreness in your forearms and wrist for a few days after doing this exercise for the first time. However, this is normal because your wrists and tendons in your forearm need a few sessions to get used to the new movement and pressure placed on them.