The delta is the difference between, represented mathematically with this symbol: Δ. A river delta is the place where the flow of fresh water meets a body of stagnant or slower moving water. Sediment builds up there, silt. It’s a fertile place, normally.
There is a significant delta between my running fitness and my cycling fitness. That they are different things is a bit cruel, but various activities tax our musculature in different ways. Fitness, generally, is the dynamic between heart, lung and muscle. How does the flow of blood carry nutrients, like glycogen, to the muscles to do work? How efficiently? For how long? What paths have been formed and how wide are they? Which part of the muscle is strong, and which is not as strong?
It’s all different, cycling, running, skiing, hiking, climbing. When you focus on one you increase the delta between it and the others. Sediments accrue.
I think the thing that was shocking for me about my adventure in New Hampshire a few weeks back was just how wide the delta was between my running and riding. A month before I’d run 30 miles in 24 hours, and found it easy. My heart and lungs are/were strong, and yet I didn’t have enough pedal strokes in my legs to make 100km on the bike easy.
On some level this is discouraging, having a lot of fitness but not being able to transfer it to all the stuff you want to do. On the other hand, it’s a good reminder that no matter how fit you are, you always live in the delta somewhere. Maybe that’s ok. No. Definitely it is.
I have, in my life, gone through periods where I focused on just one sport, and I enjoyed that and I learned a lot. But life is short and my appetite for movement is limitless. I have friends chasing all these things in all the ways, and if I want to spend good time with them I have to chase after, the jack-of-all-trades, master-of-none.
It’s tempting to see that as a negative, but let me tell you this. No matter how much time I have devoted to any one sport, I have never yet mastered a thing. Anyway, it’s all the same. The differences are superficial. The delta is the fertile spot. Everything grows there.