My running HR is vastly different in the morning vs. the afternoon. When I roll out of the rack at 6:00 am and throw on my running shoes and head out, I can fly and stay aerobic. But when I run in the afternoons/evenings, my aerobic running pace is substantially slower. Running the same splits, my HR is between 12-18 BPM faster in the afternoons. Tempature and distance do not seem to matter. The “morning effect” stays with me even if I’m going long. Caffiene doesn’t seem to have a significant effect either way. Needless to say, I do all of my aerobic running in the morning.
Am I alone on this or is it common? Does anyone have an explanation for it?