As someone who has been limited to one hour (lower intensity) rides the past six months, I think I can provide a bit of insight here: Prior to Point 1 there was epic laziness and just work-work-work, hence the lack of activity, and between 1 and 2 I was traveling, and at Point 3 I had the unfortunate pleasure of breaking my hip and elbow, which then starts the 6 months period. So between points 3 and 4 I was bedridden, not allowed to do anything, and within the first two weeks my leg muscles had shrunk by 30% I'd say. Point 4 is about 3 weeks after the accident, where the doctor said I could start with some no-resistance pedaling, every second day. About a week-and-a-half after that I started adding resistance as it was bloody boring. Two rides prior to Point 5 (6 weeks after injury), my doctor gave me a good scolding, as the X-Rays showed that the hip was still fractured. Told me to calm down. Then I had a couple of easier rides, and it was December holidays between Points 5 and 6. After Point 6 I had further X-Rays and the fracture had joined, but was not healed, but I could start adding more resistance, which I immediately did, and rode an hour every single day - until at Point 7, infection landed me in hospital for 3 nights, where again the doctor told me to take it easier. So from Point 8, I started focusing more on my physio, and alternated days between cycling and rehab, until the physio said that I'm not progressing fast enough, and should stick to physio for a week or two. At Point 9 (5 months post injury, clear X-Rays) I moved on to the biokineticst, where we measured a 30% power difference between the left and right legs, and since then I've only been doing strengthening exercises and I've ignored cycling completely. So in summary, having started from zero, an hour each day (I followed an FTP Builder plan on Zwift) really boosted my fitness quickly, but also generated long term fatigue. An hour every second day maintained fitness levels pretty well, but nothing beats a day (or two hours) out on the bike, as the two spikes just prior to point 9 indicate.
