Is Barefoot Running More Economical?

We were intrigued by the recent study of Hanson et al. [6] which reported that running in shoes (shod) requires greater rates of oxygen consumption (V˙O₂) than running barefoot. Compared to running barefoot, they reported 2.0% greater V˙O₂ for running shod on a treadmill. This difference was not statistically significant on its own, which is overall consistent with the literature [1] [2] [3] [4] [7] [8]. Only 2 [2] [3] of now 7 studies that have compared barefoot and shod running on treadmills have found a statistically significant difference in V˙O₂. One novel aspect of Hanson et al. is that they also compared shod and barefoot running overground. V˙O₂ for shod running was 5.7% greater than barefoot running. 5.7% is the greatest difference in V˙O₂ ever reported for barefoot vs. shod running. Hanson et al. did not find any special metabolic benefit for running overground in shoes. But, they suggest that barefoot running overground confers some special metabolic benefit.

An alternative explanation for the 5.7% difference could be that there was some systematic error in Hanson et al.’s experimental procedures. We believe that there was a problem with the way that they controlled overground running speed. Hansen et al. used the Nike+ system (Nike, Inc., Beaverton, OR) which determines running speed by detecting each instant of footstrike and toe-off using an accelerometer [5]. By subtracting the time of footstrike from the time of toe-off, the system calculates contact time, t_c (s). Velocity, v (m/s) can be determined knowing the horizontal distance that the body moves forward during the contact time, L_c (m) using the equation v=L_c/t_c. The Nike+ calibration procedure involves a timed 400 m run, which establishes v and the device measures the average t_c to calculate an individual’s L_c. The Nike+ system assumes that L_c for a given individual (and across conditions) does not change much at all for a range of level running speeds. We are not questioning the accuracy of the Nike+ system itself. Here, we inquire as to the possibility that Hanson et al. calibrated the Nike+ system during shod running and then utilized the same calibration to enforce speed during barefoot running. If so, a systematic bias in running speed would have been introduced in this study. Specifically, overground barefoot running speed would have been slower than for shod running. This is because t_c is systematically shorter when people run barefoot [2] [8].

For example, Squadrone and Gallozzi [8] found that at 3.33 m/s, t_c during barefoot running was significantly shorter than shod running (0.245 s vs. 0.255 s, p<0.05). Consider if Squadrone and Gallozzi had studied overground running and calibrated the Nike+ system during shod running only and then used the same calibration to control speed during barefoot running. The Nike+ system would display 3.33 m/s but the subject would actually be running barefoot at ~3.20 m/s (a 3.9% error). If a similar procedure had been followed in the study of Divert et al. [2], those authors would have unintentionally compared shod running at 3.61 m/s to barefoot running at 3.33 m/s (a 7.7% error). We are not in any way questioning the results of these earlier studies [2] [8]. Instead, we are concerned that the procedures of Hanson et al. may have incurred a systematic error in the speed of overground running such that their subjects ran between 3.9% and 7.7% slower barefoot compared to shod. Certainly, a slower ­running speed would explain, if not negate, the unexpectedly large 5.7% difference in V˙O₂ reported by Hanson et al. during overground running. If this oversight did occur, the overground data would be invalidated. With only the perfectly valid treadmill data, Hanson et al. would have concluded that barefoot running is not more economical than shod running, consistent with the majority of prior research.

• References

• 1 Burkett LN, Kohrt WM, Buchbinder R. Effects of shoes and foot orthotics on ˙VO2 and selected frontal plane knee kinematics. Med Sci Sports Exerc 1985; 17: 158-163
• 2 Divert C, Mornieux G, Freychat P, Baly L, Mayer F, Belli A. Barefoot-shod running differences: shoe or mass effect. Int J Sports Med 2008; 29: 512-518
• 3 Flaherty RF. Running economy and kinematic differences among running with the foot shod, with the foot bare, and with the bare foot equated for weight [Thesis]. Springfield (MA): Springfield College 1994; 106
• 4 Frederick EC, Clarke TE, Larsen JL, Cooper LB. The effect of shoe cushioning on the oxygen demands on running. In: Nigg BM, Kerr BA. eds. Biomechanical Aspects of Sports Shoes and Playing Surfaces. Calgary: University of Calgary; 1983: 107-114
• 5 Gaudet PJ, Blackadar TP, Oliver SR. Measuring foot contact time and foot loft time of a person in locomotion. U.S. Patent 6,052,654. April 18, 2000;
• 6 Hanson NJ, Berg K, Deka P, Meendering JR, Ryan C. Oxygen cost of running barefoot vs. running shod. Int J Sports Med 2011; 32: 401-406
• 7 Pugh LGCE. Oxygen intake in track and treadmill running with observations on the effect of air resistance. J Physiol 1970; 207: 823-835
• 8 Squadrone R, Gallozzi C. Biomechanical and physiological comparison of barefoot and two shod conditions in experienced barefoot runners. J Sports Med Phys Fitness 2009; 49: 6-13