Anchor a resistance band to a high point and stand facing it with feet shoulder-width apart. Grasp the band with an underhand (palms-up) grip and pull it down toward your chest by driving your elbows down and back while keeping your torso stable. Squeeze your back muscles at the bottom, then slowly let the band return to the start position with control, maintaining tension throughout the movement.
Log your band underhand pulldown sets in 1RM.fit and watch your estimated 1RM update automatically as you get stronger.