Running Science

by Owen Anderson

  Conclusion

  VO2max is a terrible predictor of performance among experienced runners with similar training backgrounds and has been linked with an inadequate theory of fatigue during running. However, individuals who improve their maximal aerobic capacities often enjoy significant gains in performance. A limitation on neural output seems to be the key factor which caps O2max. Overall, scientific research strongly supports the idea that high-intensity training, rather than high-volume work, produces the greatest improvement in O2max. Specific training techniques for optimizing O2max are outlined in chapter 24.

  Chapter 8

  Running Economy

  Unlike O2max, running economy is a very strong predictor of distance-running capacity.1 Scientific research reveals that running economy can sometimes account for almost two-thirds of the variation in 10K performances in a group of well-trained runners.2 Each 1 percent improvement in economy achieved during training is linked with about a 0.4 to 0.7 percent upgrade in competitive-performance time.3 Improvements in economy of almost 7 percent have been reported after as little as 6 weeks of training in highly fit distance runners, which could lead to a greater than 4 percent enhancement of performance.3

  Defining Running Economy

  Running economy is the oxygen cost of running at a specific speed; it is usually expressed in milliliters of oxygen consumed per kilogram of body weight per minute (ml • kg-1 • min-1). Runners with good running economy use less oxygen to run at a specific velocity compared with runners with less optimal economy. When runners with similar O2max values are compared, runners with better economy will move along at a lower percentage of O2max at any given submaximal speed. Economy is usually assessed in a laboratory setting with an athlete running on a treadmill while attached to a device that carefully monitors the oxygen content of the air coming out of the runner’s lungs. The difference between the oxygen content of incoming and outgoing air over the course of 1 minute is the runner’s economy.

  Why does economy have such a strong impact on performance? The percentage of O2max associated with a specific running speed is one way of expressing a runner’s economy: A runner with great economy will tend to work at lower percentages of O2max for various speeds than a runner who requires lots of oxygen and therefore has poor economy.

  The percentage of O2max associated with a particular velocity has a strong effect on how long that speed can be sustained. When well-trained ultra-runners move along at an intensity of about 67 percent of O2max, for example, they can often sustain the speed for up to 85 kilometers (53 mi) before fatigue induces a drop in pace or complete exhaustion. When fit runners cruise along at approximately 82 percent of O2max, they can complete a marathon before slowing the pace or stopping. At 94 percent of O2max, most highly fit runners can run no farther than 5K before slowing the pace.4 Therefore, if two runners competed against each other, starting at the same pace, but one runner’s oxygen-consumption rate was 82 percent of O2max while the second runner’s oxygen-consumption rate was 94 percent of O2max, the first runner could continue on for more than 26 miles, but the second runner would have to stop after just 3 miles.

  Therefore, being able to run in a quality way at a lower percentage of O2max prolongs endurance, which is why good economy is advantageous for endurance runners.

  Factors Affecting Running Economy

  The factors that affect running economy can be divided primarily into two categories: extrinsic and intrinsic.5 Knowledge of these factors can be extremely beneficial to coaches and runners. Manipulation of extrinsic factors can enhance running economy during workouts and therefore improve training quality by enhancing the speed and length of a session. Understanding the intrinsic factors leads to the creation of the best running and strengthening workouts for enhancing economy—the sessions that can optimize intrinsic economy variables. For example, ground-contact time is an intrinsic economy factor: shorter ground-contact times are linked with better running economy. Thus, coaches and runners can carry out specific drills and running routines that abbreviate ground contact and thereby promote superior economy.

  Extrinsic Factors

  Extrinsic factors that act on running economy include the effects of the environment; running surfaces; and running equipment, primarily shoes and orthotics. Increases in ambient temperature tend to enhance economy initially by moderately raising core body temperature, which increases the mechanical efficiency of the muscles. As running in the heat continues, however, further advances in core temperature spike sweat-gland activity and induce hyperventilation, which can increase the oxygen cost of running and hurt economy.6 Running into a headwind thwarts economy, while running with the wind improves it.7 Running on an incline hampers economy compared with running at the same speed on level ground,7 while downslope running upgrades economy and leads to a lower rate of oxygen consumption.8, 9 Running in shoes that contain orthotics worsens economy; running barefoot enhances economy when compared with running in shoes, even in runners who have not practiced running barefoot.10 Running on springy surfaces tends to increase economy, but running on hard, stiff surfaces can increase oxygen cost and thus may have a negative impact on economy.11

  Intrinsic Factors

  When extrinsic factors are constant, intrinsic factors—including genetic, anthropometric, kinetic, and kinematic factors—can produce considerable variation in running economy: Exercise scientists have discovered a 20 to 30 percent range in the rate of oxygen consumption associated with a particular velocity in trained endurance runners.12, 13 Some of this variation is associated with genetic factors (see discussion in chapter 2). The often-researched angiotensin-converting enzyme (ACE) gene appears to play a role. Anthropometric variables account for a significant portion of the variance, too. Research suggests that whole-body leanness, small calf circumference, and unusually long shank length (i.e., the part of the leg between the knee and foot) are associated with increased running economy.14 In contrast, having relatively large feet tends to hurt running economy,4 although some researchers contend that having feet slightly larger than normal actually promotes better stability during foot contact with the ground and thus enhances economy.

  Other Factors

  The costs of supporting body weight, exerting stabilizing force, and producing propulsive force, all done while a foot is on the ground, determine the energy and thus oxygen costs of running, and these costs can vary widely among runners.15 Scientific research reveals that runners who exhibit greater-than-usual vertical motion (i.e., more up-and-down movement of the body) during running tend to have poor economy, suggesting that directing propulsive forces vertically rather than horizontally leads to excessive rates of oxygen consumption.16

  Shorter Ground-Contact Times

  Shorter ground-contact times have also been linked with enhanced economy.17, 18 A reduction in contact time implies better control of the foot, ankle, leg, and entire body whenever a foot is on the ground during gait; time is not being wasted on the correction of nonproductive motions, so contact time decreases. Better control implies a lower need for muscular action to correct suboptimal movements and thus a reduced oxygen cost associated with ground contact.

  Shorter contact time also implies that propulsive force is being supplied by the elastic springback of stretched muscles and connective tissues rather than by active work of the muscles. Elastic springback is very economical—it requires no oxygen! It is also explosive, thus fostering quick ground contacts. Training methods designed to abbreviate ground-contact time are described in chapters 16, 25, and 28.

  Leg Stiffness

  Scientific studies reveal that economy and ground-contact time are both functions of the springiness of the legs.19 As the leg springs become slightly stiffer, economy tends to improve because more propulsive force can be created as a result of elastic recoil of the springs, not because of active, oxygen-consuming muscle contractions. As the leg springs stiffen, the leg becomes less sloppy and less collapsible during contact, permitting shorter
, more explosive contact with the ground. Thus, runners with enhanced leg stiffness will tend to have good economy and short ground-contact times, too. Runners with suboptimal stiffness will tend to have poor economy and longer ground-contact times. When running is viewed through this springiness prism, the oxygen cost of running will always be linked to contact time: As ground-contact time expands, oxygen cost increases; as ground-contact time falls, oxygen cost goes down, too.

  Although leg stiffness is often viewed in a negative light, research strongly supports the idea that reasonably increased stiffness is linked with good economy. One study looked at 11 measures of trunk and lower-limb flexibility in 100 subjects and found that the tightest (i.e., those with greatest leg stiffness) third of the runners had superior economy compared with the loosest third.20 Another inquiry carried out with 19 well-trained, subelite, male distance runners discovered that inflexibility in the hip and calf regions of the legs was associated with enhanced running economy.21 The mechanism underlying these somewhat surprising findings may simply be that tighter leg springs compared with looser, limper springs do a better job of storing and releasing energy, decreasing the need for active muscular contractions and thereby lowering oxygen cost.

  Step Length

  Other aspects of running form can influence economy, with research suggesting that a more acute (i.e., closed) knee angle during the swing phase of the gait cycle and a smaller amplitude (i.e., range) of arm motion are associated with enhanced economy.22 Step length during running can have a significant impact on economy, with research suggesting that steps that are too long can hurt economy more than steps that are too short.23 This is possibly because longer steps can produce a braking effect that increases ground-contact time and necessitates extra muscular-force production, and thus oxygen usage, to counter the braking action.

  Some research suggests that the step lengths naturally adopted by runners optimize economy,23 but it is difficult to interpret such inquiries. The basic problem is that runners may indeed select step lengths associated with the lowest oxygen costs of running, but it is also possible that they gradually become more coordinated and therefore more economical at the step lengths that are freely chosen—and less coordinated and economical at the step lengths that are not selected. Had a different step length been chosen during the early stages of a runner’s training, it might have become even more economical than the favored one.

  Certainly, there is no assurance that one’s freely chosen step length (FCSL) is automatically best for economy. In one investigation carried out with nine distance runners, researchers noted that FCSL was about 10 percent longer than the step length associated with optimal economy.24 This study provided hope for coaches and runners who believe that tinkering with running form and mechanics can lead to enhanced economy. Three weeks of training using optimal step length supported by combined audio and visual feedback gradually reduced step length and brought the oxygen cost of running under control. However, it would be risky for the average runner to change step length based on the recommendation of a coach or running peer without actual oxygen-cost measurements showing that the new stride length is indeed more economical.

  High O2max

  Somewhat surprisingly, having a high O2max increases the likelihood that a runner will have subpar economy; excellent economy is rarely linked with a high O2max.25 The mechanisms underlying this disconnect are not entirely clear, but a highly fit runner with large calves and big feet would tend to have a high O2max because of the extra oxygen expenditure associated with placing massive weights at the ends of the leg pendulums; that runner would also have poor running economy. A well-trained runner with small calves and feet might have more difficulty driving O2max up to a lofty plateau yet could enjoy good running economy. Anthropometric characteristics may make it difficult for optimal O2max and economy to occur together.

  Impact of Training on Running Economy

  In individual runners, running economy can improve or worsen over time. The following five forms of training seem to have the strongest, most positive impact on this crucial variable:

  Tapering. Reducing the quantity and quality of training over a period of 4 to 21 days can have a major impact on running economy. One study found that a 7-day taper that contained a core of high-intensity training improved 5K performances by 3 percent and running economy by 6 percent in a group of well-trained endurance runners.26

  Hill training. Research indicates that hill training can have a very strong effect on running economy. In a classic study carried out at the Karolinska Institutet in Stockholm, Sweden, the addition of twice-a-week hill workouts to a 12-week training regimen boosted running economy by about 3 percent. Chapter 15 outlines hill-training techniques that promote economy.27

  Strength training. There is convincing evidence that strength training can enhance economy in endurance runners. In a study carried out at the University of New Hampshire, six experienced female distance runners added upper- and lower-body strength workouts to their regular running programs during a 10-week training period, while six other female runners avoided resistance training and continued their usual running patterns for 10 weeks.28 The strength training led to a 4 percent improvement in economy that was not matched by the control subjects. Different types of strength training promote economy in different ways and with varying magnitudes of response (see chapters 13, 14, and 23).

  Explosive work. Explosive training (i.e., combining reps of fast running with high-speed strengthening movements, including hops, jumps, and bounding drills) is also great for economy. Research carried out by Leena Paavolainen, Heikki Rusko, and their colleagues at the Finnish Research Institute for Olympic Sports has linked 9 weeks of explosive training with an 8 percent gain in economy at a 5K running pace, the largest gain ever described in published research.29 A separate investigation carried out by Rob Spurrs and his colleagues from the Human Movement Department at the University of Technology in Sydney, Australia, found that 6 weeks of explosive drills with 15 total explosive workouts enhanced running economy by 4 to 7 percent and upgraded 3K performance time by almost 3 percent.3 (See chapters 25 and 28 for more details about explosive training as an economy enhancer.)

  Pace-specific training. Running carried out at a specified tempo is believed to enhance running economy at the chosen training speed. Indeed, research suggests that runners who bias their training toward running long miles at moderate tempos tend to become economical at moderate speeds, while runners who train at very quick paces tend to enhance their economy at faster speeds.30 Critics of this research have suggested that it is not the training per se that elicits greater economy. They contend it is possible that runners who are already economical at high speeds tend to gravitate to high-speed events like the middle distances, while competitors who are naturally economical at slower speeds tend to take up the longer competitive distances. However, research tells us that training tends to improve economy the most at the specific speed(s) that are actually used during training.31 This has important implications for the overall construction of a training plan. For example, 5K runners should include a significant amount of training at the goal 5K pace in order to optimize economy at their desired intensity, and marathoners should insert segments paced at their marathon goal speeds into their long runs. More details about speed-specific training for economy enhancement is provided in chapter 25.

  Hill training is a proven way to enhance economy.

  Conclusion

  Running economy is a critically important performance variable; both experienced and inexperienced runners can enhance running economy in a relatively short period using extrinsic and intrinsic factors. With regard to extrinsic factors, runners can improve economy instantly by shifting to barefoot running, or at least by running in truly minimal shoes. Knowledge of the importance of extrinsic factors can upgrade performance. For example, runners who are aware that downhill running lowers oxygen cost (i.e., improves economy) can speed up significantly during downhill por
tions of their race courses without augmenting their oxygen consumption rate and overall sense of effort, thus gaining an advantage over competitors who are less aware of this fact.

  Using the five key training techniques that enhance running economy—tapering, explosive work, hill training, strength training, and pace-specific effort—initiates significant upgrades in intrinsic running economy factors. Proper methods for using the five techniques are outlined fully in chapter 25.

  Chapter 9

  Minimum Velocity for Maximal Aerobic Capacity (vO2 max)

  As mentioned in chapter 7, O2max is a surprisingly poor predictor of performance. Although a runner who improves his or her O2max from 60 ml • kg-1 • min-1 to 66 ml • kg-1 • min-1 can anticipate a 10 percent improvement in performance, a runner with a O2max of 66 ml • kg-1 • min-1 is not necessarily 10 percent faster than an athlete with a O2max of 60 ml • kg-1 • min-1, nor is there any assurance that the runner with the higher O2max would out-compete the runner with the lower aerobic capacity in a 5K, 10K, or marathon. There is a significant chance that the competitor with the lower O2max would win.