Sit down on a bench and place your forearms and elbows on your legs. Your wrists should be past your knees. You should be holding the dumbbells with your palms up. This is your starting position.
Curl the dumbbells up as far as the natural range of motion in your wrists allows. Then, curl the weight back down as low as you comfortably can. Finally, repeat this entire movement for the desired or prescribed number of repetitions.
Perform this exercise in a smooth and fluid motion
Don't curl the dumbbells down too fast as this may result in injury; always be in control of the weight
SPECIAL NOTES & LEVEL of DIFFICULTY VARIATIONS
To increase the level of difficulty, slow down the movement or use heavier dumbbells.
This exercise is not for beginners. It's the type of exercise you work up to after doing more basic forearm exercises (ones that do not involve dumbbells).
The great thing about this exercise is that it will build your forearm muscles fairly quick. Also, your gripping strength will increase as well. If you feel some discomfort in your wrists while performing this exercise you may need to warm your wrists up more prior to doing this exercise. It could also mean that you are using dumbbells that are too heavy.