After turning 40, Complement's CMO Michael knew he wanted to improve his fitness.

Only instead of relying on hours at the gym, he committed to short, 15-minute high-intensity workouts 3-4 times per week.

This simple workout has lead him to be in the best shape of his life:

Here's Michael's advice:

The idea is to push as hard as possible during the 45 seconds that you're working, taking full advantage of the 15-second breaks. You'll be sweating bullets at the end if you're pushing hard enough.

I usually pick 7 different exercises, but you could also repeat a few. Here are some of my go-to's:

• • Push-ups
  • Sit-up variations (or other core/ab exercises)
  • Jump squats (or other lower-body exercises)
  • Handstand against the wall
  • Bicep curls with resistance bands
  • Down-dog pushups or another core exercise
  • Burpees or mountain climbers

But this is a choose your own adventure style workout. You can do the entire thing with no equipment (straight bodyweight), or choose exercises that use bands or kettlebells.

All you need is a Tabata timer, which you can download in the app store for free (like this one).

There's no wrong way to do it as long as it's high-intensity, safe, and fun.