I thought about riding year-round, but I don't enjoy riding when the temperature is below freezing. And I loathe riding on the trainer.
So I go to spin classes two or three times a week in the winter, and I find I'm able to start pretty well when I start riding again. Note entry on riding my age twice in February (in Arizona, not in Toronto), which included one almost-metric-century.
Come spring, I usually abandon the gym completely, but this year I have decided to focus on weights a couple of times a week instead. It's time to move some of the weight around if I can't actually get rid of it.
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Zero gallons to the mile