Rode to Hudson for the start, not sure which C loop is chosen, but put the one in from the Assabet River Bicycles website, not the one on the NVP link. Picked up the route on South Acton andd West Acton road going into Hudson. Joined the C group, and it turned out my Garmin stopped the route after I had paused it, because it had thought that the ride was finished. Also, when I started riding again, the RPM cadence did not read. Not sure why not, it has new batteries in it. I was worried at the start whether I could keep up with the group of about 12 people, including some young people and three or four women, but fortunately they regrouped occasionally and I was really not far behind, or I was toward the end of the group and never lost contact except for once, going up Liberty Square Road. Got my heart rate up over 150 which is pretty good for me! My back and butt hurt a little, but not too bad, I really enjoyed going fast, in an informal pace line, I tried to keep up. I peeled off at the South Acton West Acton road intersection with Taylor Road, where I had joined the route in the first place. Pretty tired at home. It was hot and humid earlier in the day, but was cooling off a little and getting a little drier too. Sunny, so I had put on some sunscreen. Amazingly, my average speed for the 19.5 miles I rode with the group was 17.8 mph! At about 1,000 feet of elevation too, which is not too shabby.