There’s no ifs or buts about it — at 53 years old, Jennifer Aniston is in seriously great shape. Yet unlike some other celebrities, she appears to keep her workout routine refreshingly simple — a lot of yoga, Pilates, and her 15-15-15 method. No stranger to celebrity workouts or weird and wonderful exercise challenges, I headed to the gym to give it a go. Read on to find out what happened. Of course, it goes without saying that what works for Jen might not work for you. If you’re looking for a personalized fitness plan, or you’d like to check if your form is correct during certain exercises, it’s worth chatting to a personal trainer. If you're thinking of completely overhauling your fitness routine, it's also worth chatting to your doctor. Looking for more workout inspiration? Here’s what happened when I did 100 dead bugs a day for a week , when I added planks to my morning routine , and when I tried Chris Hemsworth’s 800-rep challenge . The 15-15-15 method is far more simple than it sounds. In an interview with InStyle , the Friends actress said, “I had an injury last fall and I was only able to do Pilates, which I absolutely love. But I was missing that kind of sweat when you just go for it. I'm going back to my 15-15-15. ” The method consists of 15 minutes of cycling on an exercise bike, 15 minutes on the elliptical machine, and 15 minutes on the treadmill. All together, you’re getting 45 minutes of cardio without getting bored. Plus, you’re targeting slightly different muscles on each machine. Check out our treadmill vs elliptical comparison here, and our treadmill vs exercise bike face off here. To find out more, I set aside 45 minutes of my day to head down to the gym and try out all three machines. I’m normally a runner, clocking around 20 miles a week, and am currently training for a half marathon, so more often than not, I’ll head out on a run rather than step on the bike or elliptical. That said, I was intrigued to mix things up. It might sound obvious, but unless you have one of the best equipped home gyms out there, this is probably one you’re going to want to head to the gym for. We’ve found the best gym trials that’ll allow you to hit the gym for free here. We’ve also got the best exercise bikes and the best treadmills if you are looking to add a cardio machine to your home. So, what lessons did I learn after the 45 minutes? First, the time flew by. 15 minutes is just long enough to really push yourself on each machine, without getting bored or feeling overly exhausted. I warmed up on my jog to the gym, so when I jumped on the bike I was able to do faster sprints in the final 15 seconds of each minute. I then jumped on the elliptical, which definitely felt more chill after my 15 minutes of spinning, but still, the low-impact jogging was enjoyable. Plus, one of the benefits of using the elliptical machine is that you’re using your upper body at the same time. It wouldn’t be my cardio machine of choice in the future, but it was a nice break and still let me keep my heart rate up. Finally, I hopped on the treadmill and jogged for the final 15 minutes. Again, I realized that Jen is onto something with these short, sharp bursts — I never got to the point where I was watching the clock tick by, which normally happens to me when running on the treadmill. I finished the workout in a great mood, feeling like I’d really worked up a sweat, but also that the 45-minutes had passed really quickly. It also reminded me that I need to spend more time cross training to mix up my workout routine — a running coach once told me that your heart and lungs don’t know that you’re on an exercise bike rather than a 400m track and that there are some serious benefits to adding some low-impact cardio to a training plan. Hats off to Jen, this was a fun one that I’ll definitely be trying again. .