Planks are super-effective in targeting the core, not just for stomach toning, but for better posture too – if you spend a lot of your working day sitting at a desk, building your strength in the plank position is a great way to keep your lower back healthy.br br An easy at-home exercise, all you need is the space to lie down (just don't get too comfy!) – watch the video for our trainer Nick's top tips for planking safely.br br Watch next – more workouts with Nick and SandyMumsnet!br br UPPER-BODY: br br LOWER-BODY: br BINGO WING BLAST: br Get more fitness tips from Nick at www.nickfinney.co.uk | Follow Nick on Twitter at @finneyfitnessbr Mumsnet is the UK's biggest online network for parents. Join the conversation at www.mumsnet.