Right before Ramadan, I completed the ‘4-Week Cardio Boost with HIIT’ collection on Apple Fitness+. It consists of 12 high-intensity interval training workouts (HIIT) curated from the Fitness+ library.

The first week consists of three 10-minute sessions and is mainly squats and lunges. Most of the workouts in the collection are variants of squats and lunges. As advised in the collection, I do a new workout from the collection every other day; Monday, Wednesday, and Friday, with breaks on the weekends.

The second week has two 10-minute sessions sandwiching a 20-minute session in the middle of the week and the third week flips it around with a 10-minute session bookended by two 20-minute sessions. Finally, in the fourth week, it’s all 20-minute sessions.

I appreciate how the workout started short and with the basics; squats and lunges. It then builds up by introducing jumps, and challenges between sets. By the end of the first week I got used to squats and lunges, by the end of the second week I’d started to do (some of) the jumps, and by the end of the third week, I’d gotten used to continuing working out between sets.

I like how the last session in the fourth week, like a good end-boss fight, combined everything that I’ve done in the collection so far but makes it completely different. It was a challenge but I knew I could do it.

There were a few bumps in the way. I think introducing burpees in the second session is too soon. If I didn’t learn that doing the modifications — easier movements demonstrated by the trainer on the left — would yield the same result as if I pushed myself doing the unmodified workout but needing longer breaks, I would have dropped out thinking that the collection is too difficult.

Because the collection is a curated playlist of existing workouts in the Fitness+ library, it doesn’t feel as cohesive as the Fitness+ Workout Programs, a feature of Fitness+ that has not seen an update in a long while.

My goal for taking up the collection as a challenge, as it says on the tin, was to improve my cardio fitness. Ever since the Apple Watch could measure my cardio fitness — by monitoring my outdoor walking and running — it has complained that my cardio fitness is lacking.

At the end of the four weeks, I have more confident doing HIIT workouts, the most efficient workout on Fitness+. What I mean is I burn an average of 10 calories every minute of HIIT. A 10-minute session gets me ~100 and a 20-minute session gets me ~200 on the movement ring (Apple’s fitness matrix). In contrast, Yoga burns 5 calories every minute per session, which isn’t great when I am short on time.

Has my cardio health improved? I haven’t had a chance to go for a walk or a run since I completed the collection, so I don’t know. But I do know that I feel better and lighter, my waistline is shrinking and I’m adding more HIIT into my week’s playlist of workouts, even during Ramadan.