In my 20's I swam a mile most mornings ~40 minutes. About 30 minutes into my swim a warm rush of well-being would wash over me. With biking, I don't notice that all-at-once wash, but after my 40 minute commute each way, I feel a less intense "high". I've often wondered if the lower intensity is due to being 25 years older, or that I'm using fewer muscles. I definitely exert less on the way to work, but I push it on the way home and neither produces that "wash" like swimming did, nor do my extended multi-hour rides.