Lie flat on a bench or floor with a dumbbell in one hand and your feet firmly planted. Extend your arm straight above your shoulder. Keep your upper arm still as you slowly bend your elbow to lower the dumbbell toward or slightly behind your head. Pause briefly, then extend your arm back to the starting position by contracting your triceps. Maintain controlled movement and switch arms after completing your reps.
Log your dumbbell lying single extension sets in 1RM.fit and watch your estimated 1RM update automatically as you get stronger.