Lie on the floor with a dumbbell placed between your feet (hold the ‘bell’ of the dumbbell between the middle of your feet). Start with your feet close to the ground and from here lift the dumbbell, by bending your knees and contracting your hamstrings.Once you get to just over a 90º bend in your knees, lower the dumbbell back down to starting position. Complete your reps slowly, and make sure you always have a firm hold on the dumbbell.