Running Economy

On my 5-mile run around Lake Miramar in San Diego today, I thought about economy.

Jason Lake Miramar

People use different amounts of oxygen when running at the same submaximal speeds, and this difference explains why runners with the same VO2max do not cross the finish line together in races. This difference in oxygen use is called running economy—the volume of oxygen (VO2) that muscles consume to run at submaximal speeds. For example, when someone runs at a 10-minute mile or 9-minute mile or 8-minute mile pace, there is a specific amount of oxygen he’ll consume every minute (which gets higher the faster the pace) to maintain each of those paces. While VO2max explains what happens at the upper limit of oxygen use, running economy explains what happens at levels below that upper limit.

To understand why running economy is so important, imagine that Jason and Jack have the same VO2max, but Jason uses 70 percent of that VO2max and Jack uses 80 percent while running at an 8-minute-per-mile pace. The pace feels easier for Jason because he’s working at a lower percentage of his maximum to maintain the pace. In other words, Jason is more economical. If Jason were to run at 80 percent of his VO2max just like Jack, he’d be running faster than Jack. Therefore, Jason can run at a faster pace before feeling the same amount of fatigue as Jack. With the same VO2max and better running economy, Jason would almost surely beat Jack in a race.

Although VO2max gets most of the attention among runners, running economy is more important—it exerts a much greater influence on someone’s ability to run successfully because most of the time the person is running at a submaximal pace.

It’s difficult to determine how economical a person is because finding out exactly how much oxygen he or she uses to run at specific paces takes some sophisticated laboratory equipment. Unless the person is lightweight, an experienced runner, and was born with a lot of slow-twitch muscle fibers and mitochondria, he or she is probably not very economical. Only very talented runners are economical from the time they start running. But running economy is very responsive to training because running builds more mitochondria, makes a person a smoother runner, and helps him or her lose weight.

Running economy is influenced by many internal and external characteristics. The internal characteristics include:

Running mechanics influence economy because any unnecessary movements (and therefore unnecessary muscle contractions) increase the amount of oxygen the body consumes to maintain the pace. The more optimal the mechanics—including proper foot placement on the ground with just the right amount of pronation to absorb shock upon landing, correct arm swing, minimal vertical movement (bouncing) of the center of mass, and so on—the more economical the runner will be.

Muscle fiber recruitment. The less muscle that’s recruited to run at the desired pace, the better. Any extra muscle activity reduces economy because more muscle activity means more oxygen is being used.

Number of slow-twitch muscle fibers. Slow-twitch fibers are made for aerobic activities like running. They’re much more efficient than fast-twitch muscle fibers, which are made for sprinting.

Amount of mitochondria. More mitochondria means more aerobic factories to spread around the work, which improves economy.

Body weight. The less someone weighs, especially from the waist down and even more so from the knee down, the less work the body does to transport the person’s weight when he runs. Slim legs are more economical because they require less energy to lift off the ground. Adding weight, particularly at the end of a long lever, requires more energy to move the lever and makes the work harder.

Ability of tendons to store and use elastic energy. Like a rubber band when stretched, the Achilles tendon, which connects the calf muscle to the heel bone, stores energy when the foot lands on the ground and gives back that energy at push-off, helping to propel us forward. Long, thin Achilles tendons are good at storing energy with each step. They make the legs work like springs, which is very economical.

The external characteristics include:

Training is the biggest external factor that affects running economy. Increasing weekly mileage, adding faster-paced running to a base of mileage, and strength training all improve running economy.

Shoe weight. Lightweight shoes that still provide enough cushioning improve running economy.

Running into the wind decreases economy because there is more air resistance to overcome.

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