Set up in front of the cable machine by positioning yourself about a foot away from the apparatus. Grab the straight short bar with your palms down (reverse grip) at shoulder width apart. Tense the cable a little bit and lean back just a touch. This is your starting position.
Curl the weight up all the way until your forearms are almost completely vertical. Then, curl back down to the starting position but make sure you keep tension in your arms by not extending them completely straight. You should always keep tension in your arms/biceps for optimal movement efficiency and muscle development.
Repeat this entire movement for the desired or prescribed number of repetitions.
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 a great exercise for beginners because it's fairly low impact on the wrist joints. One thing to point out here is that you will need to have a stronger grip the heavier you go with the weight. Thus, in the beginning you may want to select a lower weight until your gripping strength increases.
The good news is that gripping strength increases fairly quick. Also, forearm muscles are relatively easy to build-up. Once you do this exercise for a while we suggest moving on to more advanced forearm exercises that involve the use of dumbbells (see complete list of forearm exercises).