Performing kettlebells curls while holding an eccentric isometric squat produces incredible levels of tension in the biceps, particularly in the top position.
Rather than leaning back at the top of the movement (a common tendency to subconsciously release tension from the biceps), the squat forces you to stay slightly leaned over. This slightly angled position, combined with the hanging nature of the kettlebells, provides continuous levels of significant tension, creating occlusion and cellular swelling.
The rigid squat position leaves little room for using momentum to help lift the weight. You have to rely solely on smooth yet forceful contractions to complete the movement. Two to three sets of 6-10 controlled reps will nail the biceps without unnecessarily fatiguing the lower body.
As an added bonus, this exercise improves lower body mobility, hip mechanics, and squatting technique. You'll have to spread the knees and unlock the hips to fit the kettlebells between your legs.