I am a recreational rider that rides 100-150 miles per week. I just finished a 70 mile charity ride a few weeks ago where I finished very strong with a personal high average for this distance. I have been very strong since especially at climbing until last week where for no reason I have extremely fatiqued legs and a heartrate that seems to be low for the given levels of exhertion. I feel like I am riding in sand where the pedals are just very heavy. I just had the bike (2005 TCR1 Composite) tuned up with new chain, brakes, etc. and initially thought this was a mechanical issue but now believe its not. I have been told that I could either be overtrained or getting ill both of which I feel are not true. I have had days where I just don't have good legs for no explainable reason, but never a prolonged period of this especially considering how strong I was just prior to this. Does the body go through natural cycles where down performance is a result? If so, how do I get out of this because I have a century ride this weekend? FYI, my weight is optimal, diet good, overall health is good. Any advice would be appreciated because this really has me bummed.