Start in a traditional plank position - shoulders over the hands and your weight on only the toes.
Make sure your core muscles are tight.
Then bring your right knee forward under your chest, with your toes just off the ground. Go then back to your basic plank. Change legs, before left knee forward.
Keep changing legs and start picking up the pace until it feels a bit like running in place in a plank position.
Continue to "run" in the plank position for 30 seconds to 1 minute.
