Place your forearms along a flat bench, pressed between your thighs. Your hands should be free at the end of the bench.
Holding the bar with palms facing upwards and 10 inches (25 cm) apart, raise and lower the hands as high and low as possible.
Do not follow the common practice of rolling the bar down the fingers between reps. This works the wrist, not the forearms.
If you want to work the lower forearms, place a 6—8-inch (15—20-cm) block underneath the back of the bench to raise the angle.