Although it is one of the most important factors determining performance in distance running, running economy is not a well-understood concept. Respected coach and author Pete Pfitzinger, the top American finisher in the 1984 and 1988 Olympic marathons, explains that running economy determines how fast you can run using a given amount of oxygen. If you can run faster than another runner while using the same amount of oxygen, then you are more economical. Running economy varies widely, however, even among elite runners.
As with many aspects of running performance, Pfitzinger explains that genetic differences play a major role in the variation of running economy between runners. In Faster Road Racing: 5K to Half Marathon, the two-time San Francisco Marathon winner details the seven primary influencers of running economy—and how running economy can be significantly improved through training:
- Muscle fiber type. The proportion of slow-twitch to fast-twitch fibers in the muscles is a key factor in a person's running economy. Slow-twitch muscle fibers use oxygen more efficiently, so the most economical runners tend to have a higher proportion of slow-twitch fibers. Although fast-twitch fibers cannot be converted to slow-twitch fibers, Pfitzinger points out that fast-twitch muscle fibers gain more of the characteristics of slow-twitch fibers through endurance training.
- Energy return. During the landing phase of a runner's stride, the muscles and tendons lengthen and store energy, which is then released as the runner pushes off. The ability of the muscles to store and return energy in a springlike action varies among runners and likely contributes to differences in running economy. “Stiffer leg muscles and tendons, like tightly coiled springs, are more effective in doing this,” Pfitzinger clarifies.
- Vertical oscillation. Since both feet are in the air during each running step, a degree of vertical movement is inevitable. Pfitzinger warns that excessive up-and-down movement is a waste of energy. “One adaptation to month and years of endurance training may be to reduce vertical oscillation, thereby developing a more economical stride,” he says. “Over time, relatively bouncy novice runners may develop into more economical veterans.”
- Body proportions. A wide range of biomechanical variables—such as the length of the femur relative to the tibia—may influence running economy, but no single aspect of body proportion is most important. Rather than any individual factor, running economy seems to be related to the complex interaction between many biomechanical variables.
- Flexibility. Pfitzinger admits that the relationship between flexibility and running economy is unclear; some studies find improved economy in less flexible runners while others find it in more flexible runners. “There may be an optimal range of flexibility below which stride length is compromised and above which there is no benefit,” he says. He reveals that leg stiffness appears to be a key element in improving energy return. In other words, excessive flexibility may be counterproductive. Maintaining flexibility while doing specific strengthening exercises to improve leg stiffness might provide full range of motion while maximizing the muscles' ability to store and return energy.
- Running skill. A common misconception in the running world is that coaches can look at a runner and tell whether he or she is efficient or economical. “Most of the differences in running economy between runners occur inside the muscles and are not obvious to even the most experienced coach,” Pfitzinger stresses. Over years of running, however, subtle changes in running technique do seem to lead to small but useful improvements in running economy as running skill improves. Several factors contribute to this, including improved timing of the firing of muscle fibers, the ability to relax opposing muscles, and reduced use of stabilizing muscles—all of which reduce consumption of oxygen.
- Fatigue level. As the muscles fatigue, runners use more oxygen to run at a given pace. This may be caused by reduced energy return and increased use of additional muscle fibers as those muscles fatigue. “This suggests that starting a race with fresher muscles by tapering training for several days may lead to an improvement in running economy during the race,” Pfitzinger concludes.
Coauthored with Running Times senior writer Philip Latter, Faster Road Racing: 5K to Half Marathon offers insights on running the most popular race distances. Runners will find detailed, easy-to-follow training plans for specific race distances so they can make the most of their training time.