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JK Speaks: Total Quality Management - Boosting The Economy
by: John Kellogg, AKA JK
September 10, 2007 (JK's birthday)

(Part 1 in a series on Running Economy)

Running economy is a measure of the energy expended by a runner to maintain a given speed and is generally indicated by the amount of oxygen consumed (i.e., the oxygen cost required) to run at a given velocity; in more general terms, the ability to translate energy into performance. When the effort is stabilized at a steady VO2 (oxygen uptake), the aerobic component of the energy demand can be found by measuring the VO2. The lower the VO2 for a steady state pace, the less energy used; hence, the better the running economy of the runner at that speed or pace. For example, if Thomas has a VO2 of 52 ml/kg/min at 6:00 per mile pace (10 mph) and Frank consumes only 47 ml/kg/min at the same pace, Frank has the better economy for that pace. Measurements of economy are taken at speeds below the runner's ventilatory threshold, due to the fact that a pace above the ventilatory threshold does not have a steady VO2. Runners with very large VO2 capacities may consume more oxygen for any given sub-threshold speed, but their running economy may or may not be relatively worse when compared to other runners.

Energy can be lost through chemical conversion of substrate (stored fuel), wasted movement, or other factors. Efficiency is the percentage of chemical energy converted to mechanical work, while running economy refers to energy expenditure vs. velocity (which is not a direct measure of total work). Therefore, mechanical work accomplished and running economy are not necessarily synonymous; if the mechanical work is not translated into forward propulsion (velocity), and energy is squandered, running economy is lower. This may be due to vertical oscillation or excessive knee or ankle flexion (among other wasteful motions), causing a great deal of work to be done with a possibly low VO2, but not a very fast pace to be sustained at that VO2.

Comparisons of running economy between athletes may be done using the measured VO2 at a given pace divided by the runner's maximal VO2 to derive a relative VO2 or % VO2max at which the runner is performing. For example, if the VO2max of the above runners are 75 and 70 ml/kg/min, respectively, Thomas is running at 69.3% VO2max (52/75 x 100%) at 6:00 per mile pace, while Frank is running at 67.1% VO2max (47/70 x 100%) at the same pace. Frank still has the better running economy at 6:00 pace in both absolute and relative terms.

Economy can also be expressed in VO2 required to cover a certain distance in a certain time. If an athlete covers one kilometer in 3 minutes and maintains a VO2 of 60 ml/kg/min in doing so, the running economy exhibited during that segment of the test could be expressed as 3 x 60 = 180 ml/kg/km.

Since glycogen supplies more energy than fatty acids per unit of O2 consumed, it is the preferred energy substrate for aerobically-demanding workloads. Since 5 kilocalories of glycogen substrate are utilized for each liter of O2 consumed, the actual glycogen requirement for a given pace can be estimated. Figuring in the contribution of fatty acids or amino acids would be more problematical, requiring the respiratory exchange ratio to determine the percentages of carbohydrate and fat which are being used as substrate. Nonetheless, bearing in mind that there is a ceiling of roughly 2,000 available kilocalories of skeletal muscle glycogen which can be accessed to produced energy, knowledge of the oxygen uptake (and, by extension, the glycogen requirement) at a steady pace can assist in determining a prudent pace for longer events in which glycogen depletion may be an issue.

Energy requirements can theoretically be estimated at efforts requiring a high anaerobic demand. In measuring lactate produced and O2 saved by glycolysis, energy expenditure is roughly 220 calories per gram of lactate formed. Accurately measuring this would be an invasive process, however, and is impractical, so running economy is conventionally determined by measuring oxygen consumption at speeds below the ventilatory threshold, where the VO2 remains steady long enough to attain accurate and meaningful measurements.

In evaluating treadmill vs. overland running economy, gait patterns are somewhat different, so if measurements are to be taken on treadmills, the test subjects should spend about a week running on the belt prior to taking any measurements of economy. Apparent changes in economy could occur as a result of establishing familiarity with the treadmill and adjusting stride mechanics during the testing period.

Runners who exhibit predominantly slow twitch characteristics generally have better running economy at speeds below the ventilatory threshold. Not surprisingly, running economy (as measured by oxygen uptake) is more important in longer distances (and is a better performance predictor for those distances) than it is for shorter distances. Also, the amount of time accumulated at a given speed over months and years, as long as the effort is not so frequently intense as to invoke wasted motion or tension, has a great bearing on running economy at that particular speed. Elite middle distance runners have exhibited extremely high economy at 4:20 per mile or faster (although the VO2 is not steady very long at that pace), while marathon runners exhibit excellent economy at 5:00 to 6:00 per mile, but each group's economy becomes worse relative to the other group when running at the other's preferred pace. This, of course, is borne out in race performances as well as in measurements of economy.

Determining all the interacting physiological factors which affect running economy, as well as how to improve economy at various speeds, is a tricky proposition. We might as well simply ask, "What makes someone a good runner?" The good news is that running economy can often continue to improve with running experience even if other standard markers such as maximum heart rate, maximal oxygen uptake, pure 100-meter speed, et cetera are not improving or are even declining.

Part 2 will examine some of those trainable physiological characteristics that influence running economy.

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