The classic biceps exercise. Load the bar with enough weight to do 8 to 12 repetitions, after a warm-up. For the working sets, approach muscle failure but don’t reach it until the final set, then on the final set you can even go beyond failure by including some forced repetitions (one, two or three, with the help of a training partner) or negative reps.
Only use the biceps for this exercise, and DON’T LET YOUR ELBOWS COME AWAY FROM YOUR SIDES otherwise the shoulders will get involved in the movement. You also have to keep your body upright. NEVER ARCH THE LOWER BACK as this takes the stress off the biceps and can cause pain or discomfort in the lumbar and sacral areas of the spine, which could lead to injury.
Returning the bar from the end position back to the starting point should be done in a controlled manner. Don’t just let it drop or bounce it back up against your body to start the movement for the next rep.
Bar curls have several variants, with the most important one being Z bar curls. The curvature of the Z bar is designed to suit your grip, which allows you to keep your wrists in a better anatomical position and (according to some) enables you to use a slightly heavier load without changing the dynamics of the exercise.
Some athletes also do curls with a straight bar or a Z bar in a seated position, supporting the load on their quads so they only perform the upper part of the movement, which enables them to really squeeze the strongest part of the muscle. It should go without saying that you must be very careful on the negative or eccentric part of the movement, and lower it in a controlled manner to avoid bouncing or rebounds.