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[[File:Paula Radciffe NYC Marathon 2008 cropped.jpg|right|thumb|300px|Paula Radcliffe, the holder of the women's world record for the marathon (2:15:25) has gained much of her improvement through greater Running Economy.]]
[[Running Economy]] is how much energy it takes you to run. The better your economy, the faster and further you can run. Running economy is obviously determined to some extent by biomechanical efficiency. Changes in things like arm movement and the amount of "bounce" can have a direct impact on running economy. However there is some evidence that biochemical changes may have a significant impact on running economy. For instance , slow twitch [[Muscle|muscles]] require less oxygen for the same level of work as fast which muscles do. Running Economy can vary by as much as 30% between runners of a similar [[VO2max|V̇O<sub>2</sub>max]]<ref name="Daniels-1985"/>. The two charts below show the [[VO2max|V̇O<sub>2</sub>max]] and running economy of Paula Radcliffe over a 10 year period<ref name="Jones2006"/>. Over that time Paula Radcliffe's race performance dramatically improved even though her [[VO2max|V̇O<sub>2</sub>max]] did not. This suggests that for elite athletes at least, improvements in running economy are critical.
{| class="wikitable"
|- valign="top"
|[[File:PR Running Economy.jpg|none|thumb|300px|Paula Radcliffe's Running Economy (V̇O<sub>2</sub> consumption at 16 Km/hr, 6:00 min/mile)]]
|}
=Shoes=
The research on how shoes effect running economy is rather confusing, with many apparently contradictory findings in some areas. Some of the problems include:
[[File:Reeves-2014-ShoeMass-RE.jpg|right|thumb|300px|Shoe mass against running economy<ref name="Reeves-2014"/>.Even on a cushioned treadmill, it appears that shoe cushioning can provide an improvement in running economy. The tests were performed at paces corresponding to various percentages of [[VO2max|V̇O<sub>2</sub>max]] (the shapes) and the vertical axis is the change in RE compared with barefoot. ]]
The results of studies that have compared barefoot and shod running (or running in un-cushioned and cushioned shoes) have provided conflicting information. Some studies show that running economy is worse when wearing shoes, with the bulk of the detrimental effect explained by the shoe weight. However, other studies have shown that the cushioning provided by shoes can compensate for the reduction in running economy due to shoe weight, and sometimes the shoes can actually be provide better economy than barefoot. I believe that the key to understanding this conflict lies in the type of running a surface that is used by the study. Not surprisingly, if a study uses a cushioned treadmill, the cushioning provided by the shoe does not confer any additional advantage over the barefoot condition. Of the 11 studies I found, 3 of the 4 studies using cushioned treadmills showed no improvement in running economy for shoe cushioning, while the 4 studies using un-cushioned treadmills and one using a cushioned treadmill showed an improvement for shoe cushioning. There were three studies that did not give sufficient information to determine the type of treadmill, and two showed no improvement while the remainder did. '''I conclude that a well cushioned running shoe can improve Running Economy by an estimated 2-3.5% compared with a weight matched un-cushioned shoe'''. In practice, most shoes will have a beneficial impact on Running Economy due to cushioning and a negative impact due to their weight.
* '''Studies on cushioned treadmills'''. Most studies tend to use cushioned treadmills, as these are the most commonly available.
** A thesis study showed that barefoot is more economic than shoed (New Balance M1500, 344-368g/shoe), but the same as shod when compensating for shoe mass<ref name="Flaherty-1994"/>. The barefoot condition had a greater [[Cadence]] than shod. The treadmill (Marquette model 1900) was cushioned.
** Habitually FFS runners are 2.4% more efficient in minimally shod (FiveFingers with) than cushioned (GEL-Cumulus 10) shoes at 9 min/mile pace and with weights to ensure equal mass<ref name="Perl-2012"/>. This study used a Vision T9250 treadmill that is cushioned, with a reputable reviewer rating as 6.8/10 for cushioning<ref name="treadmilldoctor.com"/>.
** A study compared barefoot (BFT), minimally shod (MS), and shod (SH) showed that BFT was 2.6-5.1% more efficient than SH<ref name="MooreJones2014"/>. The study also compared MS at the [[Cadence]] of BFT (165) and the cadence of SH (160), with an improvement only seen at the lower cadence. The participants had no prior barefoot or minimal running experience, and no adjustment was made for shoe mass. However, this study used a Woodway PPS treadmill with the manufacture claim that "Our patented Slat Belt running surface helps absorbs more of the impact than any other treadmill(<ref name="woodway.com"/>)".
** A study comparing barefoot running with the participants using their normal running shoes showed that barefoot condition had a 4.4% improvement in running economy<ref name="Reeves-2014"/>. However, 80% of the change in running economy could be explained by shoe mass. In fact, the slope of the line between shoe mass and running economy predicts that a shoe weighing 9.2oz/260g would have the same running economy has barefoot. The shoes used weighed between 8.5-15oz (239-430g). Interestingly while running economy improved, [[VO2max|V̇O<sub>2</sub>max]] did not. The treadmill used was a WoodWay Pro-XL, a highly cushioned "slatted" treadmill similar to the one noted above.
* Studies on un-cushioned treadmills.
** Running in lightweight (150g/5.3oz, Nike Mayfly) shoes was 2% more efficient than barefoot<ref name="Franz-2012"/>. The study used runners with a midfoot [[Foot Strike]] and an un-cushioned treadmill (Quinton 1860).
** A thesis study showed that running in lightweight shoes (Nike Mayfly) was 3.4% more efficient than weight matched barefoot, and 2.1% more efficient than barefoot<ref name="Wierzbinski-2011"/>. The study used runners with a midfoot [[Foot Strike]] and an un-cushioned treadmill (Quinton 1860). When the weight of the Nike Mayfly shoes was doubled using weights, the running economy was still better than barefoot. The study also added EVA foam to the treadmill surface, but this did not change the running economy of barefoot running. However, the cushioning was added in slabs, and participants noted that the gaps felt "like running on a trail".
** Running barefoot and in Nike 3.0 shoes had no difference in running economy on an un-cushioned treadmill (Quinton 1860)<ref name="Tung-2014"/>. However, adding 10mm of cushioning to the treadmill improved barefoot running economy by 1.9%<ref name="Tung-2014"/>. Using 20mm cushioning made no further improvement over 10mm. The cushioning was provided by EVA foam used in running shoes. (The EVA foam was fairly soft, measuring 52-58 on the Asker Type C scale<ref name="Tung-2014-PC"/>. That's about 27-33 on the Shore A scale.)
** A comparison of barefoot and shoes weighing 150g and 350g showed the same running economy in barefoot and 150g shoes, but 3.6% lower running economy in 350g shoes<ref name="Divert-2008"/>. The treadmill used (ADAL 3D, HEF-Tecmachine) appears to be un-cushioned. This study also showed that compared with barefoot, shoes reduced the total energy required to run (work) without changing V̇O<ref name="Divert-2008"/>, suggesting that barefoot is using more elastic energy, further suggesting that the barefoot condition in this study uses forefoot strike<ref name="Ardigò-1995"/>.
* '''Unknown Treadmill'''. Sadly, many studies don't explicitly state the type of treadmill used.
** Barefoot was 2.0% more economic than shod on a treadmill and 5.7% more economic on an indoor track<ref name="Hanson-2011"/>. However, the type of treadmill and indoor track was not described and may have been cushioned. No indication was given of the type or weight of the shoes used.
** Barefoot was 1.3% more efficient than running in 340g shoes, while Vibram FiveFingers was 2.8% more efficient<ref name="Squadrone-2009"/>. The [[Cadence]] was 91.2 barefoot, 88.3 in FiveFingers, and 86.0 in shoes. While it seems strange that the FiveFingers were more efficient than barefoot, I suspect this is likely to be a statistical anomaly due to the small sample size (8 runners). The runners were all experienced in barefoot running. It is unclear if the [http://www.zebris.de/english/medizin/medizin-kraftverteilungsmessung-fdmt.php?navanchor=1010043 Zebris FDM-T treadmill] is cushioned or not.
** A study using Nike Air shoes showed an average 2.4% improvement in running economy compared with firmer shoes of a similar weight<ref name="Frederick 1986"/>. The improvement in running the economy varied by individual, between 0.5% and 6%, SD=1.8%. No details of the type of treadmill used were recorded.
==Heel Rise (drop)==
=Glycogen depletion & Fat Burning=
Because burning fat requires more oxygen than carbohydrate, the switch to fat burning due to [[Glycogen]] Depletion means more oxygen is required. This does not directly change running economy as the energy required remains similar<ref name="KyrPullinen2000"/>. However, breathing rate becomes higher to supply the required oxygen, and the amount of oxygen extracted in each breath is lower, further driving the breathing rate.
=Running Dynamics (rationalize)Biomechanics=There are a number of biomechanical features of running that are relatively easily measured that may impact Running Economy.* '''Cadence'''. A review of the scientific studies showed consistently that an increased [[Cadence]] reduces shock at the hip, knee, and ankle, vertical oscillation, and ground contact time<ref name="SchubertKempf2013"/>. One study calculated that Cadence is 28% of the variation due to biomechanical differences<ref name="TartarugaBrisswalter2012"/>.
* '''Balance and step width'''. Maintaining side to side balance is estimated to cost 2% of the energy of running<ref name="ArellanoKram2011"/>. This may be due to step width, as increasing step width can reduce running economy by 11%<ref name="Arellano-2011"/>.
[[File:Step Width.jpg|right|thumb|200px|The blue line is the center line of the body and the red line indicates the center of the foot placement. The distance between the two lines is the step width.]]
* '''Arm Swing'''. While it obviously costs energy to swing the arms while running, this arm swing actually improves running economy<ref name="ArellanoKram2011"/><ref name="Arellano-2011"/>, probably by improving balance.
* '''Ground Contact Time'''. In It's a wide range of animals, from a 32g kangaroo rat to a 140Kg pony, the energy cost of running has been shown to be proportional to generally believed that the less time each foot a runner spends in contact with the ground, the more efficient they are. However, the scientific evidence is a little patchy. ** Two studies found that a shorter Ground Contact Time was indeed correlated with better Running Economy<ref name="PaavolainenNummela1999"/><ref name="KramTaylor1990Santos-ConcejeroGranados2013"/>. The energy taken to run is mostly taken with supporting the weight of the body.** Factors related to top Plyometric training for 9 weeks improved 5K times, improved running speed economy and economyreduced Ground Contact Time<ref name="Nummela-2007PaavolainenHakkinen2003"/>*** RE correlated to longer GCT*** GCT measured at 5.8-6.6 m/It's (4:37-4:04)unclear if the reduced Ground Contact Time was part of the improvement in either 5K time or running economy, then 3.3-5but it is suggestive.56 m/s*** RE measured at 3.9 mTwo studies found no relationship between Ground Contact Time and Running Economy<ref name="HeiseMartin2001"/s (6:50)*** GCT differs FFS><ref name="TartarugaBrisswalter2012"/RFS [http://www.ncbi.nlm.nih.gov/pubmed/3891372 http://www>.ncbi.nlm.nih.gov/pubmed/3891372] *** One study showed found that a longer GCT was Ground Contact Time is correlated to a better RERunning Economy, the opposite of what is generally expected<ref name="Nummela-2007"/>. However, but that study measured RW Running Economy at 3.9 m/s (6:50 min/mile), and the correlation with longer GCT Ground Contact Time was only seen at speeds between 5.8-6.6 m/s (4:37-4:04 min/mile), rather radically faster. ** Neuromuscular characteristics and muscle power as determinants Running to exhaustion may increase Ground Contact Time<ref name="FourchetGirard2015"/>. This may not tell us much about Running Economy, but it's possible that Ground Contact Time might be an indirect measure of 5-km running performancefatigue.*** 3In a wide range of animals, from a 32g kangaroo rat to a 140Kg pony, the energy cost of running has been shown to be proportional to the time each foot spends in contact with the ground<ref name="KramTaylor1990"/>. This suggests that the energy taken to run is mostly taken with supporting the weight of the body.67 m·s – 7:18*** 4'''Vertical Oscillation'''. It seems obvious that greater Vertical Oscillation is going to be less efficient, but the research is not there to support this. One study noted "The intuitive perception is that oscillation is adversely related to economy" but found no supporting research<ref name="Anderson1996"/>.17 m·s 6:26*** CV Greater vertical impulse on a force plate related to lower RE but noted exceptions to this seem common<ref name= 4"HeiseMartin2001"/>.5, 6:00*** FurthermoreIn 16 national level runners, REtrack2 correlated greater Vertical Oscillation was associated with improved Running Economy, the mean CT opposite of what would be expected<ref name="TartarugaBrisswalter2012"/>. The study found that Vertical Oscillation accounted for 7% of constant velocity laps during the 5K (r variation due to biomechanical differences. ** A 1997 study found elite runners have less Vertical Oscillation than sub-elite runners<ref name= 0"CavanaghPollock1977"/>.64, P ** Running with exaggerated Vertical Oscillation reduces Running Economy< 0ref name=" Tseh2008"/>.001)This suggests that it's possible to use excessive bounce to intentionally compromise your running, and might indicate that some runners could have a problematic level of Vertical Oscillation, but there is no clear evidence to indicate that's the case. *** REtread A study of 31 runners found that there was measured as a steadynon-state oxygen uptake (V·O2significant relationship between increased Vertical Oscillation and reduced Running Economy, U mL·kg-'''0with the most economic runners having a Vertical Oscillation of 9.1cm and the least economic having 9.6cm<ref name="Cavanagh1987"/>.75'''·min-1) (38)*** Longer GCT has greater VO2 cost (poorer RE)Running to exhaustion may increase Vertical Oscillation<ref name="FourchetGirard2015"/>, which might make Vertical Oscillation a metric for evaluating fatigue.** Explosive-strength training improves 5-km Vertical Oscillation tends to decrease with increased Cadence<ref name="HalvorsenEriksson2012"/>. This makes perfect sense from a simplistic model of running , as a higher cadence means that each stride is shorter, so less time by improving running economy and muscle poweris spent in the air where the runner is in a ballistic curve. This relationship can confuse the analysis of Running Economy, as it's easy to attribute changes in Cadence to Vertical Oscillation, or Ground Contact Time.*** Interesting – explosive training improves REFeedback to reduce Vertical Oscillation resulted in impaired Running Economy<ref name="HalvorsenEriksson2012"/>. The study used real-time feedback to encourage runners to reduce their Vertical Oscillation, decreases GCTbut the study lasted a relatively short time. It's possible that the impaired Running Economy was a result of the initial change in biomechanics rather than indicating that reduced Vertical Oscillation is actually a bad thing. Of course, but control group has increased GCTthe other interpretation is that there is an optimal level of Vertical Oscillation and attempting to reduce it is actually a bad thing.* '''Foot strike. '''It's often assumed that a forefoot landing is more efficient than a rear foot landing, but there's no clear evidence to support that.** No A study found that while there was no difference in running economyRunning Economy between different foot strike types, but there was a higher work for FFS produced with Forefoot Strike, suggesting more elastic storage<ref name="Ardigò-1995"/>.** No difference between FFS/MFS A study looked at runners with different foot strike patterns and RFS except for compared them running with their habitual RFS doing FFS had a lower economystride and intentionally modifying to an alternative foot strike<ref name="GruberUmberger2013"/>. The study found no differences with the exception of rear foot strike runners changing to a forefoot strike.** Subelite RFS is Sub-elite rear foot strike runners are more economic than MFS. Cadence midfoot strike, and while a cadence was the same, but contact time greater in RFSthe rearfoot runners had a higher Ground Contact Time<ref name="Ogueta-Alday-2014"/>.=Body weight and fat percentage (intro)=The relationships between body weight, body fat, and running economy are not what you might expect.
* '''Body Mass'''. Greater body mass is associated with better running economy<ref name="Bourdin-1993"/><ref name="Bergh-1991"/>. This may be because larger individuals can store more elastic energy on each step to reduce their energy consumption<ref name="Taboga-2012"/>.
* '''Body Fat'''. Perhaps surprisingly, obese individuals have similar running economy as leaner individuals<ref name="Taboga-2012"/>. Remember that running economy is energy used divided by weight. So the heavier you are, the more energy required overall, and more body fat results in a lower power output. So being overweight reduces your fitness (aerobic capacity) but not your running economy.
=DOMS=
[[Delayed Onset Muscle Soreness]] reduces running economy<ref name="BraunDutto2003"/><ref name="Smith-1992"/>. This matches most runners experience, as it's tough to run with DOMS. My personal suspicion is that DOMS damages the muscle fibers that are used first, and these fibers are the most trained and the most efficient.
=Flexibility=
[[File:Standing External Hip Rotation.jpg|right|thumb|200px|Greater Standing External Hip Rotation reduces running economy.]]
* '''Stretching Programs'''. Most studies show that [[Stretching]] programs do not reduce running economy<ref name="Nelson-2001"/><ref name="Godges-1993"/>.
* '''Stretching before running'''. One study<ref name="Wilson-2010"/> has shown that stretching directly before running reduces performance and running economy, but most studies indicate no impact<ref name="AllisonBailey2008"/><ref name="Hayes-2007"/>, even though the stretching impairs other muscular functioning. (One study on subjects with limited hip range of motion showed that stretching before running improved running economy<ref name="Godges-1989"/>, but the subjects were only tested with 4 minutes of running, and a steady state requires 4-15 minutes<ref name="Morgan-1989"/>).
=Gender =
Women may improve their running economy in response to training more effectively than men<ref name="Bourdin-1993"/>.
=Framework for Factors Effecting Running Economy=
[[File:Factors affecting running economy.jpg|none|thumb|500px|A schematic of the factors effecting running economy<ref name="Saunders-2004"/>.]]
=NotesConcerns with Measuring Running Economy=Most studies use Oxygen use as a proxy for energy use, but this is not always accurate<ref name="FletcherEsau2009"/>. Measuring Running Economy is reasonably repeatable, with a CV Coefficient of Variability of ~1-2%, though these variation variations are sufficient to cause issues in determining changes in economy due to different situations<ref name="Morgan-1994"/>.
=References=
<references>
<ref name="GuLi2013">Effect of Shoes' Heel Height on the Energy Cost during Jogging, Y.D. Gu and Z.Y. Li, Research Journal of Applied Sciences, Engineering and Technology July 15, 2013</ref>
<ref name="Brown2013">The Acute Effect of Heel to Toe Drop on Running Economy. Brown, Harrison and Silva, Robert (2013). Undergraduate thesis, Fort Lewis College</ref>
<ref name="HeiseMartin2001">Gary D. Heise, Philip E. Martin, Are variations in running economy in humans associated with ground reaction force characteristics?, European Journal of Applied Physiology, volume 84, issue 5, 2001, pages 438–442, ISSN [http://www.worldcat.org/issn/1439-6319 1439-6319], doi [http://dx.doi.org/10.1007/s004210100394 10.1007/s004210100394]</ref>
<ref name="Anderson1996">Tim Anderson, Biomechanics and Running Economy, Sports Medicine, volume 22, issue 2, 1996, pages 76–89, ISSN [http://www.worldcat.org/issn/0112-1642 0112-1642], doi [http://dx.doi.org/10.2165/00007256-199622020-00003 10.2165/00007256-199622020-00003]</ref>
<ref name="TartarugaBrisswalter2012">Marcus Peikriszwili Tartaruga, Jeanick Brisswalter, Leonardo Alexandre Peyré-Tartaruga, Aluísio Otávio Vargas Ávila, Cristine Lima Alberton, Marcelo Coertjens, Eduardo Lusa Cadore, Carlos Leandro Tiggemann, Eduardo Marczwski Silva, Luiz Fernando Martins Kruel, The Relationship Between Running Economy and Biomechanical Variables in Distance Runners, Research Quarterly for Exercise and Sport, volume 83, issue 3, 2012, pages 367–375, ISSN [http://www.worldcat.org/issn/0270-1367 0270-1367], doi [http://dx.doi.org/10.1080/02701367.2012.10599870 10.1080/02701367.2012.10599870]</ref>
<ref name="CavanaghPollock1977">Peter R. Cavanagh, Michael L. Pollock, Jean Landa, A BIOMECHANICAL COMPARISON OF ELITE AND GOOD DISTANCE RUNNERS, Annals of the New York Academy of Sciences, volume 301, issue 1 The Marathon, 1977, pages 328–345, ISSN [http://www.worldcat.org/issn/0077-8923 0077-8923], doi [http://dx.doi.org/10.1111/j.1749-6632.1977.tb38211.x 10.1111/j.1749-6632.1977.tb38211.x]</ref>
<ref name="Cavanagh1987">Relationship between distance running mechanics, running economy, and performance. / Williams, K. R.; Cavanagh, P. R. In: Journal of Applied Physiology, Vol. 63, No. 3, 1987, p. 1236-1245.</ref>
<ref name=" Tseh2008">author Tseh W, Caputo JL, Morgan DW, Influence of gait manipulation on running economy in female distance runners., J Sports Sci Med, 2008, volume 7, issue 1, pages 91-5, PMID [http://www.ncbi.nlm.nih.gov/pubmed/24150139 24150139], 3763358 !!pmc!! </ref>
<ref name="FourchetGirard2015">François Fourchet, Olivier Girard, Luke Kelly, Cosmin Horobeanu, Grégoire P. Millet, Changes in leg spring behaviour, plantar loading and foot mobility magnitude induced by an exhaustive treadmill run in adolescent middle-distance runners, Journal of Science and Medicine in Sport, volume 18, issue 2, 2015, pages 199–203, ISSN [http://www.worldcat.org/issn/14402440 14402440], doi [http://dx.doi.org/10.1016/j.jsams.2014.01.007 10.1016/j.jsams.2014.01.007]</ref>
<ref name="HalvorsenEriksson2012">Kjartan Halvorsen, Martin Eriksson, Lennart Gullstrand, Acute Effects of Reducing Vertical Displacement and Step Frequency on Running Economy, Journal of Strength and Conditioning Research, volume 26, issue 8, 2012, pages 2065–2070, ISSN [http://www.worldcat.org/issn/1064-8011 1064-8011], doi [http://dx.doi.org/10.1519/JSC.0b013e318239f87f 10.1519/JSC.0b013e318239f87f]</ref>
<ref name="PaavolainenNummela1999">Leena M. Paavolainen, Ari T. Nummela, Heikki K. Rusko, Neuromuscular characteristics and muscle power as determinants of 5-km running performance, Medicine & Science in Sports & Exercise, volume 31, issue 1, 1999, pages 124–130, ISSN [http://www.worldcat.org/issn/0195-9131 0195-9131], doi [http://dx.doi.org/10.1097/00005768-199901000-00020 10.1097/00005768-199901000-00020]</ref>
<ref name="PaavolainenHakkinen2003">L. Paavolainen, K. Hakkinen, I. Hamalainen, A. Nummela, H. Rusko, Explosive-strength training improves 5-km running time by improving running economy and muscle power, Scandinavian Journal of Medicine and Science in Sports, volume 13, issue 4, 2003, pages 272–272, ISSN [http://www.worldcat.org/issn/0905-7188 0905-7188], doi [http://dx.doi.org/10.1034/j.1600-0838.2003.00340.x 10.1034/j.1600-0838.2003.00340.x]</ref>
<ref name="Santos-ConcejeroGranados2013">Jordan Santos-Concejero, Cristina Granados, Jon Irazusta, Iraia Bidaurrazaga-Letona, Jon Zabala-Lili, Nicholas Tam, Susana Gil, DIFFERENCES IN GROUND CONTACT TIME EXPLAIN THE LESS EFFICIENT RUNNING ECONOMY IN NORTH AFRICAN RUNNERS, Biology of Sport, volume 30, issue 3, 2013, pages 181–187, ISSN [http://www.worldcat.org/issn/0860-021X 0860-021X], doi [http://dx.doi.org/10.5604/20831862.1059170 10.5604/20831862.1059170]</ref>
</references>
