For guys who lift regularly, the top part of their shoulder muscle (trapezius) works differently when doing overhead presses — it doesn’t ramp up much with kettlebells and doesn’t respond as strongly to heavier weights, which might mean it’s more about keeping things stable than powering the movement.

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 shoulder presses sitting down with a kettlebell instead of a dumbbell that weighs the same, their shoulder and back muscles seem to work a bit harder — maybe because of how the kettlebell is shaped and balanced.

When guys who lift weights do the lowering part of a shoulder press, using a kettlebell makes the front shoulder muscle work harder than using a barbell — probably because the kettlebell is less stable and harder to control.

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.

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.