The way I feel in the morning reminds me that rest is a vital part of the training cycle.
Transportation and commuting cyclists might think they're exempt from training schedules. In cooperative terrain, over fairly short distances, that's probably true. But as you age you will notice slopes and distances you formerly considered trivial. If you ride a longer average daily distance over bigger hills you can easily fall into a destructive pattern in which you ride at moderately high intensity all the time.
Traffic cycling often feels like a race. Dense traffic feels like a criterium, but even on the open road I find that motorists seem more respectful if I maintain a good cadence and appear strong. That doesn't mean charging every hill in the big ring. That takes a lot out of you and still looks feebly slow to the pilot of a ridiculously over-powered motor vehicle. Just maintain good pressure on the pedals and keep your head up. Day after day, mile after mile, that's enough to sap you by the end of the week if you don't stretch and rest when you get home.
The effect comes on gradually. You might hammer through your thirties and most of your forties on caffeine and over the counter pain meds (or worse), but at some point you will have to accommodate the realities of physiology.
Racers face this fact early in their careers or they have no career. To race successfully, even as field fodder, you can't beat the crap out of yourself all the time and expect to have any pop on race day. My own results were mediocre, but I learned that principle from a member of the US Olympic cycling team for 1980. A few of us in Annapolis were fortunate to ride with Thomas Prehn when he lived there. He taught us right away to avoid the "half fast" pace that breaks you down without the benefit of a well-defined difference between effort and rest.
Unfortunately, the half fast pace can afflict many commuters trying to keep their schedule. On my commute I face the same hills over the same 14.3 miles. Leaving my rural neighborhood I share the road with people who act like they just got home from NASCAR fantasy camp, on a somewhat hilly two-lane road. Three miles of that leads to state highways for about seven miles before density begins to pick up again going into Wolfeboro. The road narrows sharply as the traffic packs into one of three primary feeder routes into town. It's a small town, but it strangles a couple of numbered highways, so traffic in or out of town mixes with frustrated drivers just passing through. It's a place to keep your elbows out and your attitude up.
Going home I add some distance to avoid some tight spots. The longest route makes about a 34-mile day with a really stiff climb on the way home. That route is quite restful, because the nasty climb is on a dirt road through the woods, but it's still a tad over 17 miles with a lot of climbing after a long day on my feet at work.
Standing up for hours after sprinting to work fills my legs with the chemicals of fatigue. I have to carve out a few minutes here and there to stretch a little during the day.
Interestingly, riding the fixed gear bike a couple of days a week seems to help loosen things up. Maybe the fact that it forces the legs to move constantly helps flush out the muscles on the downhills rather than letting them sit idle as they would while coasting on a freewheel bike. Even so, after yesterday's sprint on the rain bike and last night's long zoning board meeting my legs feel like they've been pummeled. Today needs to be a rest day. Ideally I will hit the rollers and then stretch after I get home tonight. Either that or pop 12 ounces of carbohydrate beverage and hit the couch. As long as I elevate my legs it counts as part of training.