It's 3pm and your eyes are drooping and productivity cratering. What do you do?

For some a cup of coffee is the obvious solution, but experts warn that caffeine later in the day can lead to sleep difficulties. You could try chocolate for a quick jolt, but as we all know there some pretty obvious nutritional downsides to that plan as well.

So are you doomed to jangly nerves, excessive calories or a miserably exhausted afternoon? Nope, says a helpful new study published in the journal Physiology and Behavior. The research identified a simple intervention that manages to beat that old-stand-by, caffeine, for boosting focus and motivation.

And here's the best part: it's absolutely free, dead easy, and requires no special equipment.

Step your way to more afternoon energy

The study had a straightforward premise. The researchers recruited a group of chronically sleep-deprived college students (all of whom described themselves as typically getting less than 6.5 hours a night) and offered them one of two possible mid-day energy boosts. One group took 50 milligrams of caffeine, about as much of the stimulant as a can of soda. Another simply walked up and down stairs for 10 minutes at a moderate pace. (A third group acted as a control.)

What was the result of this head-to-head match-up of possible pick-me-ups? A battery of cognitive tests and subjective reports of motivation showed that caffeine actually did little to energize the flagging students. However, those who took a few minutes to patrol the stairways did show a moderate but significant boost in energy and motivation. This dead simple and always available exercise was the clear winner.

No excuse not to give it a try

As Patrick J. O'Connor, study co-author and professor of kinesiology at the University of Georgia points out, the simplicity of this science-backed solution to the afternoon slump means you have no excuse not to give it a try.

"Office workers can go outside and walk, but weather can be less than ideal. It has never rained on me while walking the stairs," he joked, adding that "you may not have time to go for a swim, but you might have ten minutes to walk up and down the stairs."