Start standing with your feet hip-width apart. Hold a dumbbell in each hand in front of your hips with your palms facing your body. Draw your shoulder blades down and back, and engage your core and pelvic floor. Bend your knees slightly. This is your starting position.
Hinge forward from your hips to lower the dumbbells along the front of your legs, stopping halfway down your shins (or as low as is comfortable). You should feel tension in your hamstrings (the backs of your legs). Ensure that you maintain a straight back and that you keep your neck straight in line with your spine rather than looking up or down.
Then, using your glutes and hamstrings, reverse the movement to lift your torso and return to the starting position. That's one rep.