Anthony blogs about productivity and time-of day here. I find it interesting that the time of day folks are the least productive is the time of day I am most likely at the gym. Trust me, I have my highs and lows, but at 2:16 on Monday/Wed/Friday (usually), I'm gearing up for some elliptical action and trying to talk myself out of my fitness program (and then I have to talk myself back in...my internal dialog is exhausting). Just about to head off to the gym now.
You can all roll your eyes and groan as I say what I am about to say, but I think a big part of the problem is that people eat too many processed carbohydrates and refined sugar. I mean, eat what you want, of course, but I have noticed the difference in my energy level since I have changed my diet and the impact having some peanut butter or an orange has on my workout.
I didn't see any mention of food or sleep in the article so I'll consider the survey interesting trivia. But I think we can all come up with reasons why people peter out at those times and what they can do to fix it. Power nap anyone?