If you're under pressure to get more done, the worst thing you can do is work longer hours. That's the message in this month's Harvard Business Review, where Tony Schwartz says the key to productivity is managing your energy, not your time.

Schwartz is the president and founder of The Energy Project in New York and a co-author of The Power of Full Engagement (Free Press, 2003). He told Kathleen Melymuka how to do more high quality work in less time and get your life back in the process.

You write that working longer hours isn't the solution to the increasing pressure many of us feel at work. Why?

Because the fundamental mistake that organizations make with their people is to treat them as machines -- indeed as computers. Companies make the assumption that people can operate for very long periods at high speeds running multiple programs at the same time. In fact, human beings are not designed to be linear, but rather to pulse -- to move between expenditure of energy and renewal of energy. When we establish that rhythm, we're most productive and most sustaining. Instead, we've begun mistaking activity for productivity. "More" has become the measure of success. The more things we do, the more tasks we juggle, the more hours we work, the more we're rewarded. But the real measure should be the quality of our output -- the value we add at the end of the day. We've lost sight of that.

What's the alternative when you've got deadlines that don't move?

Managing energy rather than time is more efficient. Here's an example: When I wrote a book about this work, I had a very, very tight deadline -- three months. I had written three books before and none had taken less than a year. But rather than working more hours, I actually worked fewer. I worked in four 90-minute "sprints" a day and I didn't allow myself to be interrupted during those work periods. In between each work period, I fully disengaged for 20 to 30 minutes -- and by that I don't mean I surfed the Web or answered e-mail. Instead, I either had something to eat with my family, took a run or spent time reading the newspaper. I was vastly more efficient when I was working because I wasn't interrupted. And when I wasn't working, I was truly refueling. I wrote the book in 90 days working half the number of hours each day that I had for previous books.

Tell me about the four main dimensions of energy.

The first level is physical. That's the core energy any human needs to get out of bed in the morning and do what he needs to do. Corporations typically haven't considered that business-relevant. But if a person doesn't have sufficient physical energy, there's no way she can think at her best, manage her emotions effectively and or feel any passion about what she's doing. The keys are pretty simple: eating frequently and nutritiously in small portions, working out regularly, sleeping sufficiently and taking at least short breaks every 90 to 120 minutes during the work day. If you've got those nailed, you're in great shape. The problem is that virtually no one we work with does have those nailed.

What might, I, a typical IT worker, be doing wrong in that area?

I think IT workers may be among the most challenged about taking care of themselves physically, because they so often get addicted to their computers. They fail to change channels. The more time you spend in front of that screen -- continuous time -- the more depleted you get. It's critical during the day to physically move, disengage, eat, have a conversation about something other than work, get outside.

How do emotions play into energy?

We learned from our years of work with elite athletes that they all feel the same way when they're performing at their best: optimistic, focused, happy, calm. In short, positive emotions serve performance. If you're not feeling positive emotions, you can't perform at your best. Negative emotions engage the sympathetic nervous system: fight or flight. Thinking and focus degrade, and because all emotions are contagious, negative ones drag the people around you down, too.