Last two times I've done an audax, the following week has seen a big lift in speed (about 3kph average over the week), with 3 days later as a peak. I set my commute PB on the wednesday after my only 300, and after this weekend's 200, today I went the fastest I've been since then.
My sense is that when I ride with "proper cyclists" they do silly things like ride in the big ring, and stand up when going up hills. I have to go into my reserves just to stay on their back wheel, so it briefly teaches me to ignore my body shouting "stop it you are hurting me".
Is it a common thing? Does anyone else feel stronger after a 200 or 300? Any idea on the mechanism and how I can keep it going?