Back Extensions work your lower back, with a particular focus on the erector spinae, as group of muscles which work to straighten and rotate the back. You will also be working your neck muscles and some stabilising muscles, such as the multifidus. Working your back is really important, especially when you do lots of core work as your lower back is actually part of your core! This exercise will also help to correct any rounding in your back.
For this exercise we will start lying on our front, facing down towards the floor with our fingertips to temples. Exhale and lift your head and chest up, away from the floor, pause at the top and then come back down in a controlled manner. We are aiming to keep our feet in contact with the floor so that our back continues to work and we do not let our strong glutes and hamstrings take the workload.
To progress this exercise, at the top of the movement you can extend your arms out in front of you and bring them back in before coming back down. This will lengthen the time for which you are holding the position increasing your 'time under tension' and will increase the workload for your lower back due to the increased weight ahead of you.