Stand facing a cable machine with a high pulley and attach a straight bar. Grasp the bar with an underhand (palms-up) grip shoulder-width apart. Keep feet shoulder-width, core braced, and elbows close to your sides. Pull the bar down toward your chest by engaging your lats, squeezing at the bottom. Pause briefly, then slowly return to the starting position under control.
Log your cable underhand pulldown sets in 1RM.fit and watch your estimated 1RM update automatically as you get stronger.