How do we decide whether to walk or run?
Imagine yourself walking on a treadmill that starts at a reasonable pace: say, two and a half miles per hour. Every two minutes, the treadmill increases its speed by 0.2 mph: 2.7 mph, 2.9 mph, 3.1 mph, and so on. If you’re in good physical condition, at some point — usually between about 3.0 and 4.5 mph — you’ll find it more comfortable to start running instead of walking. Different individuals have different thresholds based on their fitness level and other factors, but even taking these things into account, it’s difficult to explain exactly why people start running when they do. Do different people have different thresholds for pain?
Gregory Daniels and Karl Newell paid 12 physically fit college students to walk on a treadmill as it gradually increased in speed. To disguise the real purpose of the study, the students were fitted with fake oxygen consumption meters and cardiographs. They were told to walk, but to begin running as soon as it felt more comfortable. They also rated their physical exertion every two minutes by pointing to a numeric chart on the wall (remember, their mouths were covered with the oxygen consumption meters so they couldn’t talk).
But most importantly, the walkers were also sometimes asked to complete simple addition and subtraction problems. Every 10 seconds, a new tape-recorded problem and answer was played, and the walkers had to raise their right hand to indicate a correct answer and raise their left hand for an incorrect answer. They repeated the experiment four times: two times with no math problems, and once each with easy (single-digit) and hard (double-digit) math problems. Here are the results:
