Introduction
There are various ways to evaluate and measure an individual’s capacity for endurance performance. Along with variables such as lactate threshold, critical power, and VȮ2 max, running economy can influence an individual’s endurance and be a predictor of performance. Running economy can be defined as the energy demand for a given speed or pace.[1] Within the act of running, there are different modes, including uphill running and downhill running. These two modes have significant physiological and biomechanical differences. These differences in running modes could affect an individual’s cardiorespiratory responses and this could cause a change in running economy.[2]
Running Economy
Running economy can be determined by evaluating an individual’s steady-state oxygen consumption at a sub-maximal running pace.[3],[4],[5] Individuals with a good running economy are those that use less energy and less oxygen while running at a given speed.3,[6] Those with similar a VȮ2 max can have up to a 30% difference in running economy and it can be a better indicator of an individual’s endurance performance than that of VȮ2 max.4,5,6 A study by Saunders et al showed that a 5% improvement in running economy correlates to a 3.8% increase in running performance.3
Conley et al looked at the correlation between running economy and running performance of 12 highly trained endurance runners. They evaluated their oxygen uptake during a steady-state submaximal run and a VȮ2 max test. They found that even though these runners had similar VȮ2 max levels, there was still variation in their 10km finish times. The authors concluded that running economy accounted for the variations seen in 10km performance among the runners.[7]
Those with similar a VȮ2 max can have up to a 30% difference in running economy and it can be a better indicator of an individual’s endurance performance than that of VȮ2 max.4,5,6 Elite runners with similar VȮ2 max values tend to have a better running economy.[8]
Running economy is an important measurement for distance runners.6 It can be difficult to measure running economy while individuals are running outside, so it is mostly done in laboratories with portable metabolic devices that measure oxygen uptake.6
Many different factors can influence a person’s running economy and it can vary among runners.8 Several factors that can affect running economy may include physiological components and an individual’s biomechanics.[9],[10] Biomechanical differences could include stride rate and length, ground contact time, and velocity. Changes in heart rate and minute ventilation also have the potential to affect running economy and those with a better running economy are associated with a lower heart rate and minute ventilation.3,6 An increase in these factors has also been shown to decrease running economy.3
Studies have shown that the economy of one mode of exercise cannot accurately predict the economy of another mode of exercise and individuals could have different efficacy levels across modes of exercise.1 Various characteristics can contribute to changes in running economy.6 The differences found in the different running modes of uphill and downhill running could affect an individual’s cardiorespiratory responses leading to changes in running economy.[11]
Uphill and Downhill Running
Uphill and downhill running has significant physiological and biomechanical differences.1 Uphill running uses greater propulsive forces and a majority of the work needed for this is provided by the hip muscles.11,[12] Within the act of uphill running, as the grade increases, there is an increase in step frequency.[13] Uphill running is also associated with a shorter swing phase and a longer stance phase. During uphill running, lower extremity muscles create roughly 28% greater muscle activity, in comparison to level running.13 EMG activity is greater in the gluteus maximus, rectus femoris, and biceps femoris during uphill running.13
Downhill running uses greater braking forces and high amounts of eccentric loading.1 Downhill running includes longer air time and a reduction in step frequency.13 Downhill running is associated with a longer stride length. 13 In downhill running it has been shown that there is lower vertical displacement.13
Downhill running is associated with an increase in negative external work, which is the work that is needed to decelerate an individual’s center of mass.13 At -5°, downhill running is associated with a high impact force, and leg shock increases by 30%.13,[14] Vertical impact force peak also increases by 14%.14
Cardiorespiratory Factors Associated with Uphill and Downhill Running
Respiratory responses during downhill running such as VO2 and minute ventilation are lower when running at the same velocity.[15] Cardiac responses such as heart rate and O2 pulse were also lower in downhill running.15 This may lead to decreases in stroke volume and arteriovenous O2 difference.15 Individuals involved in an uphill and downhill running study were found to have an inverse slow component of VO2 and heart rate during downhill running. 15 This inverse slow component in downhill running may be coming from a decrease in ATP demand associated with downhill running.15
Breathing patterns can vary with downhill and uphill running. Breathing frequency was found to remain the same during uphill and downhill running. 15 However, in downhill running, VO2, heart rate, and minute ventilation were lower compared to uphill running.15 This may be due to downhill running having a superficial minute ventilation pattern.15
Energy Cost of Uphill and Downhill Running
Certain factors may contribute to the energy cost of graded running, or the amount of energy that is used during a specific distance.[16] During uphill running, the energy cost of running may be due to cardiopulmonary factors.16 During downhill running, the energy cost of running is more related to biomechanical factors such as stride rate, contact time, and step frequency.16 Having a higher stride length, lower ground contact time, and a higher step frequency may be correlated with a lower energy cost of running on downhill slopes.16
Conclusion
Running economy can be a predictor of endurance performance. The running economy differences in uphill versus downhill running are due to various factors, including anatomical and biomechanical. The differences found in the different running modes of uphill and downhill running could affect an individual’s cardiorespiratory responses, leading to changes in running economy.11 Future studies should focus on what factors, anatomical/biomechanical, influence an individual’s uphill or downhill running economy. The results of such a study can help determine what type of individual is better suited for uphill or downhill running.
[1] Breiner TJ, Ortiz ALR, Kram R. Level, uphill and downhill running economy values are strongly inter-correlated. Eur J Appl Physiol. 2019 Jan;119(1):257-264. doi: 10.1007/s00421-018-4021-x. Epub 2018 Oct 24. PMID: 30357515.
[2] Li, F., Newton, R. U., Shi, Y., Sutton, D., & Ding, H. (2019). Correlation of Eccentric Strength, Reactive Strength, and Leg Stiffness With Running Economy in Well-Trained Distance Runners. Journal of strength and conditioning research, 10.1519/JSC.0000000000003446. Advance online publication.
[3] Saunders PU, Pyne DB, Telford RD, Hawley JA. Factors affecting running economy in trained distance runners. Sports Med. 2004;34(7):465-85. doi: 10.2165/00007256-200434070-00005. PMID: 15233599.Aug;115(8):1725-33. doi: 10.1007/s00421-015-3156-2. Epub 2015 Mar 27. PMID: 25813019.
[4] Daniels, J., & Daniels, N. (1992). Running economy of elite male and elite female runners. Medicine and Science in Sports and Exercise, 24(4), 483–489.
[5] Moore IS. Is There an Economical Running Technique? A Review of Modifiable Biomechanical Factors Affecting Running Economy. Sports Med. 2016;46(6):793-807. doi:10.1007/s40279-016-0474-4
[6] Barnes KR, Kilding AE. Running economy: measurement, norms, and determining factors. Sports Med Open. 2015;1(1):8. doi:10.1186/s40798-015-0007-y
[7] Conley DL, Krahenbuhl GS. Running economy and distance running performance of highly trained athletes. Med Sci Sports Exerc. 1980;12(5):357-360.
[8] Pate RR, Macera CA, Bailey SP, Bartoli WP, Powell KE. Physiological, anthropometric, and training correlates of running economy. Med Sci Sports Exerc. 1992;24(10):1128-1133.
[9] Chen TC, Nosaka K, Tu JH. Changes in running economy following downhill running. J Sports Sci. 2007 Jan 1;25(1):55-63. doi: 10.1080/02640410600718228. PMID: 17127581.
[10] Kubo K, Miyazaki D, Shimoju S, Tsunoda N. Relationship between elastic properties of tendon structures and performance in long distance runners. Eur J Appl Physiol. 2015
[11] Li, F., Newton, R. U., Shi, Y., Sutton, D., & Ding, H. (2019). Correlation of Eccentric Strength, Reactive Strength, and Leg Stiffness With Running Economy in Well-Trained Distance Runners. Journal of strength and conditioning research, 10.1519/JSC.0000000000003446. Advance online publication.
[12] Roberts, T. J., & Belliveau, R. A. (2005). Sources of mechanical power for uphill running in humans. J Exp Biol, 208(Pt 10), 1963-1970. doi:10.1242/jeb.01555
[13] Vernillo, G., Giandolini, M., Edwards, W. B., Morin, J. B., Samozino, P., Horvais, N., & Millet, G. Y. (2017). Biomechanics and Physiology of Uphill and Downhill Running. Sports Med, 47(4), 615-629. doi:10.1007/s40279-016-0605-y
[14] Gottschall, J. S., & Kram, R. (2005). Ground reaction forces during downhill and uphill running. J Biomech, 38(3), 445-452. doi:10.1016/j.jbiomech.2004.04.023
[15] Lemire M, Lonsdorfer-Wolf E, Isner-Horobeti ME, et al. Cardiorespiratory Responses to Downhill Versus Uphill Running in Endurance Athletes. Res Q Exerc Sport. 2018;89(4):511-517. doi:10.1080/02701367.2018.1510172
[16] Lemire M, Remetter R, Hureau TJ, et al. Energy Cost of Running in Well-Trained Athletes: Toward Slope-Dependent Factors. Int J Sports Physiol Perform. 2021;17(3):423-431. Published 2021 Dec 1. doi:10.1123/ijspp.2021-0047
