This exercise is called the "single-leg, single-arm, Romanian deadlift" and provides a great leg workout. Men's Health gives the details on this exercise, which as well as blitzing your hamstrings, glutes, and lower back, this move will strengthen your core muscles and stabilizer muscles.
Stand holding a dumb-bell in your right hand at arms length in front of your right thigh. Lift your right foot off the floor. Keeping your knee slightly bent and your back flat, push your hips back to lower the weight towards the floor. Try to go as low as you can without rounding your back and bouncing at the bottom. Pause, then push your hips forward to return to the starting position.
Stand side on to a mirror to check your range of movement and to ensure that your back remains flat as you execute this move. Complete your reps on that leg before swapping to the other side to complete your set.
This exercise works the hamstrings, glutes and lower back, as well as the core and stabiliser muscles. We recommend that any exercise programme has some form of deadlift variation incorporated to maintain healthy hamstrings and a strong lower back. Neglecting these muscles can often lead to muscle imbalance and injury.