Time management and balancing energy levels

Time management is a big issue for many of us. I've spent a fair bit of time trying to get better at it.

I read Covey and Merrill's First Things First, which I thought was pretty solid, if perhaps a bit abstract and heavyweight. Probably it's main point is that you have to focus on what counts rather than what is urgent.

(I've also heard quite good things about David Allen's Getting Things Done, though I haven't read it.)

I'd say I'm not bad at it now, but I realised that I'm lacking a good understanding of something that is crucial to time management - balancing your energy levels. You can easily get worn out and not be very productive. So you need to take time out to refresh and recuperate.

That's pretty obvious. But isn't so obvious how to, in practice, actually do it effectively. So yes, if you rush through things that can drain your energy, but then if you're totally relaxed and take as much time as you want, you won't be so productive - so the question is, where is the sweet spot?

Or take exercise as an example. They say that exercise gives you more energy. But how much exercise should you do? (And are some types of exercise more effective in this regard than others?) What is the sweet spot, so you end up having the most amount of productive time for getting things done?

The key point is that you really need to have a good understanding of the factors that effect your energy levels, and how they do so, and how much they do so, so that you can effectively manage them.

Of course, the details would vary from person to person but I suspect there's enough common ground there to at least weed out common, and ineffective, misconceptions about balancing energy levels. If there's not a book on this already -- and I haven't seen one -- there's an opportunity for one to be written. Ditto for personal consultants on this -- like a type of personal trainer for managing your energy levels.