Ok, I think I officially hit the tired phase. Having done this a few times now, I know it will pass. But right now it's like my body is saying "Whoa! OK, I've put up with the extra activity for several days straight now and I'm thinking we should take a break." Which I will not, of course, and my body will adjust to the increased demands. But until then, my limbs feel heavy and in the middle of the day I see I've done 70 push ups and I think "oh no, is that all?".