After his narrow victory in the next to the last stage of the Tour de France, Tour champion Alberto Contador commented that he had not been feeling too good, had not slept well, and had a stomach ache. In fact, he'd had physical struggles over the entire 2,200 mile race. He commented to reporters, "Cycling is not like mathematics." He might have added, "because our bodies, no matter how well trained or fed, are unpredictable and complex."
Some days when you go out exercise or compete, you feel and perform just the way you hoped. You've got the groove. But sometimes you don't. You're not sick or injured, you just start into your run or ride or lifting routine and your strength or energy just isn't there. Don't feel bad - this happens to elite athletes as often as it does to the rest of us.
Sometimes you know the cause. Yesterday I did a kettlebell workout and jumps, leaving my legs tired (the squats were a killer). Today I went for a post-work trail run, with temperatures in the mid-90s under a blazing sun. Ttwenty steps up the trail, I knew each step would be tough going.
Just as often you don't know why your bio has no rhythm. Maybe you haven't recovered enough from your last exercise session (which is what happened to me) so the glycogen levels are low and your system is busy repairing micro-tears in your muscles. You haven't allowed adequate time for recovery. Or maybe you have some stress at work or in your life that is running you down. Or you are not eating nutritious food.
It's very normal to have days like this every now and then. Just because you don't feel your best doesn't mean you shouldn't proceed with your workout. You might start feeling better after your warm-up. Even if you never feel great that day, you still get the benefits from the exercise. Years ago I read an interesting book called Maximum Performance by a UCLA physiologist who had worked with many elite Olympic athletes. Once he did a survey of people who had set world records, asking how they felt minutes before their event that day. Surprisingly, many complained that they had trouble sleeping the night before, had indigestion, and felt weak. Yet, like Contador, they won.
However, you want to be on alert if this lethargy or "just ain't got it feeling" occurs on several consecutive days. You might be over-training. A good way to find out is to know your normal resting pulse in the morning an hour after you've gotten out of bed when you've been feeling good. If it starts drifting up over a period of days, say 4-6 beats more per minute, you know you've been pushing too hard and need to take more time off before your next workout or lower the intensity of it. An exercise journal is useful to see if something is changing and what might be the cause.
Most times on days when you don't feel so great but go ahead and continue your workout, you're glad you did.
Even if you're slow and struggle, you still feel better afterwards. Exercise is a drug with very positive side effects.