CNN posted an interesting article the other day, which I'll link below. They basically tested running and cycling indoors vs outdoors, to see which was "better", where better is defined as burning more calories, getting injured less, etc. The results were interesting because they line up with my intuition. I've always disliked running on treadmills; it's boring, and I feel like I get a lot more sore. From yoga I know the dangers of repetitive motions; every step on a treadmill is the same, and it "burns out" certain muscle groups. Conversely, I've always enjoyed riding outdoors but I feel like I don't get very good exercise that way. Indoors, in a spin class for example, I sweat like a pig, but outdoors I often can't keep a consistent cadence because of real-world things like stop lights. Of course, riding outdoors is amazing and fun and I do it because it's very rewarding, but in terms of sheer exercise, I feel like I need to go at least 50% harder outdoors, which is exactly what this article found. It's a really interesting article, and I highly recommend reading it if you're interested in the topic. One concrete takeaway for me is that I don't commute by bicycle for exercise as much as I used to. I feel like it's a better use of my time to drive, and then hit up a spin class. Of course there's other excellent reasons to ride a bike, like reducing pollution. But for places far away, it's just a better use of my time to drive.
http://www.cnn.com/2016/04/07/health/treadmills-bikes-indoors-versus-outdoors/index.html