I need to strengthen my lower back. I’m just finding it aches mainly as a result of lying down, sitting on chairs, sitting on floor(prolonged inactivity would sum it up). I also race go karts where you use the back(& backside)a lot when driving & a strong back definitely helps. Mid 40’s, 180cms & just on 80kgs. I mainly weight train at the gym & haven’t focused much on back/core which I’d like to now. Any suggestions on what might suit(machine or free)would be appreciated.