When you're working against a busy schedule, it can be hard to squeeze in time for lunch some days, let alone get to the gym. But if you're serious about making fitness a priority and you've got 20 minutes to spare, this bodyweight exercise routine—developed by certified military physical training specialist Mark Lauren—will help you get in shape, even if you're crunched for time.

Here are five of Lauren's favourite moves from his book, You Are Your Own Gym, along with variations to give yourself a bit of a challenge.