Ah, the plank . Some version of it is used in virtually every type of fitness program, from CrossFit to calisthenics to yoga to pilates, and for good reason. As a core exercise, it’s hard to beat, because it trains all the muscles — from your shoulders to your glutes — to work together to support your body. It’s good for improving your posture, balance, and overall fitness.Once you’re able to hold a plank for a full minute while maintaining your form, you might be tempted to go even longer. But don’t. Eventually, some muscles will give out sooner than others, which will lead to imbalances — and likely, undue strain on your neck and shoulders.What's an even better way to boost the benefits of the plank? Variations. Challenge your whole body by adding movement in your limbs while keeping the core strong. This way, you’ll be training your muscles to work together, which is what they have to do in everyday life. Don’t hold any one version for more than one minute, but feel free to do multiple sets, resting for 30 seconds to a minute between them.We’ll kick things off with a refresher on your basic plank, but keep clicking for the moves you can (and should) do to challenge yourself.