Perfect Running Pace Revealed

So Livescience.com posted an article regarding a study at the University of Wisconsin - Maryland regarding running efficiency in terms of calories per kilometer. While the article and study is interesting of it's own, the author makes a rather grand statement to present his slant on the study:

"The most interesting finding: At slower speeds, about 4.5 mph (13 min/mile), the metabolic efficiency was at its lowest. Steudel explains that at this speed, halfway between a walk and a jog, the runner's gait can be awkward and unnatural."

This entry has quickly permeated the net, primarily due to the wording of the article and the way it's being perceived. As an example, one comment on the article reads as:

"posted 03/30/2009 08:18:18 AM

gid wrote:

I'm wondering, is walking at 4.5 (with a low metabolic efficiency) good for losing fat? am I right to assume that low metabolic efficiency means that more energy is expended per hour and per kilo? "

Similar comments appeared on Diggs and Running Ahead along the same lines, mostly of form like "they must have used elites in the study, because a 7:13 pace is very hard to me to maintain", that sort of stuff.

This is where you, as the reader, need to look closely at what's being said. The Running Ahead link is of particular interest as it presents graphs used in the study. These graphs show the data from the 9 subjects, each with a Y axis presenting energy consumption as calories per kilometer, and the X axis as pace as meters per second. Viewing them as is, you can't help but think "it must be easier to run at that faster pace than a slower pace". And...you would be wrong.

It's a quick an easy conversion to change the graphs to show energy consumption per minute (instead of per kilometer). The conversion is straight forward:

(CaloriesPerKilometer * PaceAsMetersPerSecond) / 16.667

for each point.

I picked the second graph entry for an example, applied the conversion and my values came out roughly as:

2.0 m/s = 10.3 calories/minute
2.4 m/s = 11.7 calories/minute
3.0 m/s = 13.5 calories/minute
4.0 m/s = 16.7 calories/minute
4.5 m/s = 20.4 calories/minute

The lowest energy consumption is where you would normally expect it, at the slowest pace (2.0 m/s). In comparison, the study graph shows the lowest calories/kilometer (~73 cal/k) occurred at a much higher 3.7 meters per second, about the average for the males in the subject.

To look at the original graph, you would think this subject would find it easiest to run at 3.7 m/s. However, they will be consuming about 15 calories/minute at that pace (and sucking in all the oxygen to burn it), while slower paces, as we would normally expect, consume energy at a slower pace (and thus you breath easier too).

What you can notice is the sizeable jump in energy consumption per minute once you pass that noted 'sweet spot' of 3.7 m/s. From 2.0 to 3.0 m/s (increase of 1.0), your rate goes up by 3.2 calories per minute. Same from 3.0 to 4.0 (increase of 1.0), about 3.2 calories per minute. However, go from 4.0 to 4.5 (only 0.5), energy consumption goes up 3.7 calories per minute, more than twice the increase rate than below the 'sweet spot'. It get worse from there, the curves from the original study are parabolic so the energy demands per minute will increase dramatically as pace goes up beyond that point.

What this all means, don't be fooled into thinking there's a magic and quick pace where running becomes remarkably easy and you'll become a highly efficient running machine. Sure, you'll use less energy over a given distance, but the barrier for most runners sits at the energy consumption rate per minute, not per mile (or kilometer), because that's what dictates how hard the effort feels and how hard you have to breathe to keep up.

The article misleads the reader into thinking something that's not true.