Over the last three years, I’ve regularly commuted by bike - thirteen kilometers each way pre-pandemic, now I’m down to five each - and until recently, it’s gone smoothly. To my surprise (especially since I have no stamina running) I didn’t much mind the thirteen km on my heavy three-gear commuter bike and didn’t even blink at the five.
And then I got my saddle, which was way too low, adjusted at my LBS one or two weeks ago, and ever since, I suck. I don't feel like there's much of a difference in how I'm pedaling, my speed is about the same or even slightly better, but the spikes in heart rate and feeling of pressure on my chest that make me a terrible runner come sneaking up on me on a sustained but not all that heavy climb. I don’t think it’s anything serious - I’m in my mid-twenties, don’t smoke, and heart disease doesn’t run in the family - but I do wonder why my stamina tanked so hard and how I get it back. Is it just that I’m using different muscles/using my muscles differently now and need to get used to it?