Ready to Exercise? Check Your Watch

"One recent study, by the late Thomas Reilly and his colleagues at the Research Institute for Sport and Exercise Sciences at Liverpool John Moores University in England, found that people’s maximum heart rates and sub-maximal heart rates were lower in the morning but that their perception of how hard they were working was the same in the morning as it was later in the day.

Dr. Reilly and his colleague Jim Waterhouse, in a review published this year, also noted that athletes’ best performances, including world records, were typically set in the late afternoon or early evening."

http://www.nytimes.com/2009/12/10/health/nutrition/10best.html