The hammer curl is an exercise which is primarily targeted towards hitting the brachioradialis, a hard-to-hit muscle which is part of the biceps, but, as anyone who has tried them before will know, they also significantly work the forearms because of the disadvantaged vertical grip of the bar.
Dumbbells are our weapon of choice for hammer curls. The movement is very simple. Holding a dumbbell in each hand, arms by your side, palms inward, simply curl both dumbbells up to your shoulders, giving a squeeze at the top, and then slowly lower. The elbows should be kept tucked by the side throughout the movement.
The movement can also be performed singularly, one arm at a time, also known as ‘alternating’. The movement is exactly the same, but one arm does a repetition, and then another does one. Doing it this way gives your arms slightly more time to rest, which may either be beneficial or detrimental to your goals. So I suggest incorporating both methods of hammer curl for the best results.
Many bodybuilders would have it that performing hammer curls, which help to build the brachioradialis also help to ‘lengthen’ the bicep muscle, which is particularly useful for lifters with ‘short biceps.’
While I certainly don’t believe it’s possibly to lengthen bicep muscles – as this would involve shortening tendons – I do believe hammer curls it helps to give the bicep a much more full and complete look, making hammer curls very useful indeed.