SETUP: Sit up straight on a bench (you can use the bench for extra support or not). Take a neutral-grip (palms facing in) on some heavy dumbbells and let your arms extend. Try to keep your chest up & shoulders pinned back throughout this exercise.
REP: Curl the weights up towards your shoulders by squeezing your biceps hard. Grab the weights as if you’re trying to burst them, this will engage your forearms and allow them to assist as much as possible (That’s a great thing, as the target muscles here is the biceps brachialis, the long head of the biceps which snakes down around the forearms, too).
TIP: Don’t worry if you can’t curl the weight up to shoulder level on this exercise. Anything over 90 degrees is a good rep. When the going gets tough, most people can’t get all the way up while keeping their elbows locked in place.