I have been training for a 50 mile ride coming up on the 30th of april. I started in feb. and have 420 miles in so far. This week I feel realy week and the rides that I usualy do feel harder. my times and average speeds are down. At the beginning of each ride this week My legs felt spent right off the starting block. Do I need to take some time off the bike? I have two weeks untill the big day. How should I use them?