March 31, 2009 -- When your gym teacher told you to run a mile, you wondered whether it was better to go fast and get it over with or go slow and try to conserve energy. Which approach would make you more tired?
The answer to this riddle, according to a new study, is that each person has an optimal pace in which they can cover the greatest distance using the least amount of energy. This information, interesting to runners and trainers, also offers clues about evolution.
For the study, nine participants ran on a treadmill at six different speeds. Researchers measured each participant's metabolic rate at every speed, using a device that provided a breath-by-breath analysis of oxygen consumed and carbon dioxide produced. Participants ran at all six speeds on five different days during a three-week period.
The optimal speed for women was typically slower than for men. The women averaged an optimal speed of 6.5 miles per hour (about a 9-minute mile), and males averaged an optimal speed of about 8.3 miles per hour (about a 7-minute mile). Researchers said the difference likely had to do with height and weight -- the men were typically taller with longer legs -- than with other gender differences.
The slowest speeds, about 4.5 miles per hour (a 13-minute mile), were the least metabolically efficient. This could be because walking very fast and running very slow can be physically awkward.
Researchers view this research as important to understanding evolution. As humans have become taller and longer limbed, they have become more efficient runners and walkers. When they had shorter legs and less defined waists, more like apes, their bodies may not have been as suited for hunting.