Isolated forearm flexor burn.
Keep your forearms planted. Only the wrists move through the full range.
The wrist curl isolates the flexors on the underside of your forearm, and letting the dumbbells roll all the way down to your fingertips sneaks in finger strength work most lifters never do. With your forearms pinned across your thighs, nothing else can jump in and help. The payoff is grip that holds out longer on deadlifts, rows, and carries.
It extends the range and forces the finger flexors to re-grip the weight under load on every rep. Skip it and you lose half the exercise, the wrist portion alone is a short movement.
Higher reps with strict control suit them best, the range is short and the joint is small. Forearms also recover quickly, so training them several times a week is fair game.
Palms up trains the flexors underneath the forearm, palms down trains the extensors on top. They are two halves of one pair, and training both keeps the wrist balanced.
