Attach a single handle to a low pulley on a cable machine. Stand facing the machine and grab the handle with one hand using an underhand (supinated) grip. Keep your elbow close to your torso and your upper arm stationary. Curl the handle upward toward your shoulder by bending your elbow, squeezing your bicep at the top. Pause briefly, then slowly lower the handle back to the starting position with full control. Complete all reps on one arm before switching.
Log your cable one arm curl sets in 1RM.fit and watch your estimated 1RM update automatically as you get stronger.