Stand upright holding a pair of medium-weight dumbbells or kettlebells in each hand, arms at your sides, with your knees slightly bent.
Keeping your arms straight, knees slightly bent, with your core engaged, slowly bend at your hips (not your waist) and lower the weights as far as possible without rounding your back, which should remain straight.
Now squeeze your glutes to slowly pull yourself up (don't use your back).