Heels on the ball, curl it in for sneaky-hard hamstrings.
Keep your hips lifted as you curl, don't let them drop when the ball comes in.
This makes the hamstrings do their two jobs at once, holding your hips bridged in the air while curling the ball in with your heels, which is exactly the double duty that makes it so much harder than it looks. There is no machine pad doing the stabilising for you, every inch of the roll is your hamstrings against a ball that wants to escape sideways. It is arguably the best hamstring exercise you can do with no weights at all.
Because they are working at both ends, holding the bridge and curling the ball, often in a shortened position they rarely train. Ease in with fewer reps and a slower tempo, the cramping settles as they adapt.
The machine isolates the curl and lets you load progressively, the ball adds the hip-extension hold and stability demand for free. If you train at home the ball version covers hamstrings remarkably well on its own.
Squeeze your glutes hard before the ball moves and think about lifting your hips higher as your knees bend. Hips dropping is the number one cheat, and it turns a hamstring exercise into a rest.
