I'm on my fifth day of biking every day.
I decided at the end of July to start at the beginning of August so that it would be easy to count how many days I've biked, to keep up my resolution. I thought of starting this for several months this year, thinking of how to slide into it easily. Then I realized the months were slipping by without my starting it, and the summer when it's easier to start was slipping by. Conclusion: Start whether it seems easy or not, like my life depends on it. I'll figure out whether it was exactly the right decision later on, instead of letting that worry prevent me from starting when it will very likely be a good decision in hindsight.
An interesting incident from the second day:
I went too many miles too fast, because I was excited by exploring a new bike path and didn't want to wait until I was in shape to go that far. I thought I "bonked" on the way back. The "bonk" may have been a combination of a number of types of exhaustion: dehydration, hypothermia* from having clothes wet with sweat as the day cooled into evening, low blood sugar, out-of-breath**, sore muscles, and sleepiness. The overall effect was that my pedaling was not just weak as in normal tiring, I started feeling like maybe I should just take up walking instead of biking. I felt a desire to sit down and rest at the very next park bench by the path.
When I sat down, my perception of the situation went from a narrow focus on getting somewhere, to realizing how incredibly tired I was and how much I needed to rest and to catch my breath, to resting and taking in some calm, to waking up to the need to get home and my sensitivity to perception and awareness being enhanced. Except my ability to bike wasn't enhanced. I felt weak enough that I didn't pedal at all downhill, and discovered more subtle downhills than I was aware of on previous rides. When I did try to pedal it was like going weak in the knees, not being able to put much force in, and although I didn't feel dizzy, when I went over bumps the bike shook almost out of control. Because of those effects, I walked up every hill and across every road crossing for the rest of the way back, more like stumbling, for safety's sake, not knowing how much more damage I might do to myself in that unusual state. Plus it was dark, since the ride was taking a lot longer than I had planned.
And yet, I liked the experience overall, for the effect of enhancement of perception and enjoyment, which continued for a couple of hours afterwards.
What I learned from the fifth day:
Even if your muscles are sore, that does not mean you can't get out there and bike a useful amount. When I'd had sort legs all day and felt sure it wouldn't be a good idea to go very far, I was able to go a mile away easily, and come back with plenty of energy. The spinning seemed to work the soreness out of my legs by increasing the circulation, so my legs weren't sore afterwards.
In conclusion: Why biking?
The overall reason for biking although it isn't natural, is that civilization judges us for whether we walk or run (or stand or sit) and makes it difficult physically, with pavements and traffic, to choose walking or running by instinct. Bicycling lets a body get out there and let loose any amount of energy it feels like, whether it would count as walking or jogging or sprinting uphill if on foot. You can't tell very well how much energy you're putting into it, unless you have a bike computer that measures that, because even if you can estimate how fast you're pedaling and with how much force, to multiply to estimate power, those quantities are constantly changing, and your perception of them changes as you get excited or tired. It's a good thing that you can't tell how much energy, because it lets you just take out energy that's otherwise pent up in the constraints and self-consciousness of civilization. Taking out energy as your body desires helps your whole nervous and physical system adapt better to living.
Notes added August 8:
* Instead of hypothermia, I may have experienced increased core temperature, which sports medicine says may lead to muscle relaxation and changes in neurotransmitters. (See Runner's High: Is It for Real? at MedicineNet.com and 20 Proven Health Benefits of Exercise at Health24.com, benefit number 5: Exercise is an excellent de-stressor.)
** Instead of out-of-breath, I may have experienced hyperventilation, because of breathing more in anticipation of out-of-breath.