Planned to go about 35 miles, continuing north along the river for a few more miles and then climbing out of the valley and into the country side .... but it was pretty apparent at 13 miles that the previous 6 days caught up to me. Couldn’t figure out why the legs felt so bad until Mark asked about other rides lately. Oh. Yeah. Every other day this week. So ended up cutting short the test of the new 27.5 x 1.9 wheels/tire combo. The hope was to get them on pavement too and see how that works. Anyway decided to stay on the flat and return to Riley’s Lock via towpath, the dreaded and usually avoided out-and-back. Fortunately able to draft behind Mark, else it would have been quite the death march. Legs were just .... dead. Cardio was fine; contact points fine; everything else fine. Except for the legs.