Last year I had completed 57 weeks in a row of very steady cardio, ultimately culminating in my two proudest bike rides, both imperial centuries.
This year I had worse luck, spending 13 weeks off the bike (with no extra cardio). 6 weeks were due to laziness in winter, 3 were due to a knee injury in April, and 4 were due to being hit by a car in July/August. I'm now back on the bike beginning my 5th week in a row tomorrow, but my endurance is gone. Last year this weekend I did my first 100 mile ride, having done a few metrics before it. This year, anything over 40 miles puts me in a weird place. I start feeling bad, my body starts swelling, my muscles lose power. I just feel utterly exhausted. Even this mornings 35 mile ride had me feeling like death the last few miles.
My theory is that the 57 weeks of solid cardio last year had built up a nice base, something which I am lacking this year due to almost 3 whole months with no cardio for the year so far. Is this expected? There's a metric century in 2 weeks that I really want to try, but at this point I'm having some serious reservations about it.
I should note that my speed is at an all-time high. Last year I was lucky to average 12mph for an entire month, this year I'm on track to hit 2 months in a row at 15.0mph. It's only my endurance that seems lacking.