Our expert says:
Recovery rate is quite an important component of getting fitter, so don't despair, something is working!
But seeing to the thyroid possibility is certainly something worth doing, that will at the very least either confirm or disprove a possibility.
Dealing with the next issue, the fact that you don't feel fitter, were you running 1 hour when you began training? Because that's a massive amount to start with. So would I be guessing wrongly if I suggested that when you started, you probably would not have been able to run for 1 hour? If that's true, then you have gotten fitter, by quite a margin.
The other thing that jumps out is that you are running quite fast - 6 min/km is no mean feat, and I again would like to see if that's the speed you ran at when you began, because it's pretty impressive if it's true. Is it possible that you just haven't picked up that you are fitter because you have increased the running duration or speed unconsciously so that exercise feels just the same as before, even though it's not? That does tend to happen sometimes...
But I think have your thyroid checked out and then just give it some time and let's see how it goes now that you have reached a level of training that is reasonably good. What you do next is see for example if you can get that 30 minutes run to 12km/h, obviously over some weeks, not all in one go.
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