When strong male lifters do overhead presses, using a kettlebell makes the forearm muscles work harder than using a barbell — probably because the kettlebell wobbles more and is harder to grip.

When male athletes do overhead presses, using a kettlebell makes their lower back muscles work harder than when using a barbell — probably because the kettlebell is less stable and wobblier.

When male athletes lower a kettlebell during a shoulder press, their upper trap muscles work harder than when using a barbell—probably because the kettlebell wobbles more and needs more control.

When guys who lift weights do a shoulder press with a kettlebell instead of a barbell, their butt muscles work way harder to keep them stable.

Using a heavier kettlebell during shoulder presses activates key shoulder-blade muscles way more than a light dumbbell — up to 72% more, according to this claim.

When guys lift weights overhead using a shaky bar with weights swinging off it, their core and shoulder muscles have to work harder than when using a regular, steady bar.