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13 Running Terms Every Runner Should Know

Fartlek, VO2 max, proprioception: running jargon may sound like a foreign language, but brushing up on this vocab primer of new and relevant terms will make you a better athlete.


Elastic recoil

This is quite possibly the most important single contributor to running success that almost no runner knows about. Recoil refers to the ability of your connective tissue (e.g., tendons, fascia) to store energy each time it’s stretched and then release that energy as your muscles contract, simultaneously shortening the connective tissue. The best example of this is your Achilles tendon, which is significantly stretched during every stride. Recoil provides up to 50 percent of the propulsive force for each running stride.



A split can mean two different things. First, it can refer to time recorded en route during a race, usually at evenly spaced junctures. For example, if you’re running a 5K, you might want to know your time at the first mile, which would be your “mile split.” Running “even splits” means you maintain the same pace for each split. A “negative split” means you picked up the pace over the final portion of the race.

The second way runners use “split” is when dividing a workout into parts. On distance runs, you might want to check your splits at each mile using a GPS watch. And during an interval workout, you’ll record a split for each repetition. Runners often target specific splits during repetition training as preparation for upcoming races, where they hope to hit the same split times on their way to the full race distance.



Fartlek is Swedish for “speed play.” As a workout, it’s an unstructured blend of multiple paces aimed at challenging both aerobic and anaerobic fitness. After an initial warm-up, runners alternate surges with recovery intervals. The surges can last anywhere from seconds to minutes. As initially conceived, fartlek included long repetitions, sprints, and hills, all with recoveries at easy running pace. But fartlek invites innovation. For example, Coach Joe Rubio of the Asics Aggies recommends runners alternate surges and recovery periods between telephone poles. Other runners prefer predetermined time repetitions over uneven terrain that includes hills, trails, grass, or roads, with the recovery improvised by feel.



The tempo run is probably the most misunderstood workout in running. A tempo run is a sustained running effort lasting 10–40 minutes (sometimes longer for advanced distance runners) at a pace you could maintain for at least an hour. Coach Jack Daniels popularized the workout in his book, Daniels’ Running Formula, in which he described tempo effort as “comfortably hard.” Because tempo stimulates training adaptations that are beneficial for both aerobic energy production and the removal of the detrimental byproducts of anaerobic energy production, tempo is a favorite workout among long-distance runners. Unfortunately, many runners treat a tempo run as a time trial (simulated race), negating many of its benefits while leaving themselves exhausted for their next workout.


VO2 max

This is the maximum amount of oxygen that your body can “consume” in a minute. In other words, it’s the maximum amount of oxygen that your aerobic system is capable of using to create energy. You improve VO2 max by improving your body’s ability to transport oxygen (your cardiovascular system) and to use that oxygen at the cellular level. The higher your VO2 max, the more aerobic energy you can produce.


Running economy

This measures how efficiently you use oxygen at a given running speed. If one runner requires less oxygen to run the same pace as another runner, that first runner is said to have better running economy. It’s analogous to a car getting better gas mileage.



This refers to your brain’s ability to track your body’s position in space and to then adjust your body’s movement accordingly. The brain receives sensory feedback from a network of nerves located in your muscles, ligaments, organs, and inner ear. Proprioceptive decision-making then guides your body through activities that vary from walking a straight line to reaching for your alarm clock in the dark. As a runner, you use proprioception to negotiate uneven terrain, run through soft sand, and land on your foot in a way that minimizes the possibility of a sprained ankle. Proprioceptive training improves posture, stride length, and foot strike, among other aspects of your running.


Age grading

With age grading—important for those over age 40—each runner’s finish time is scored as a percentage of the maximum performance expected at that runner’s age, with 100 percent being the top predicted score. The maximum performance for each age is determined by a curve of all age group world records for the race distance. For example, a 40-year-old man running a 16-minute 5K would earn an 85 percent age grade, but a 50-year-old man running the same time would score 92 percent. A 50-year-old woman would need to run 18:10 to achieve the same 92 percent. Your finish place is determined by your age-graded percentage, which allows runners of different ages to compete against one another.


Repetitions vs. Intervals

Runners use the terms repetitions and intervals interchangeably, although purists will argue that they have different meanings. For most runners, repetition and interval training both refer to workouts in which you run multiple short segments (e.g., 8 x 200 meters, or 3 x 1 mile) at a given pace, separated by recovery periods during which you walk, jog, or just stand around. Technically, the “repetition” is the hard running segment, and the “interval” is the rest between each repetition. Interval training originated in the 1930s (building off similar workouts from the 1920s) as a way to increase stroke volume (how much blood your heart can pump with each beat).



Running “aerobically” means that you’re running at an effort level (pace) that is almost entirely fueled by aerobic energy. Aerobic energy is created within your cells and can’t be produced without oxygen. Of course, aerobic energy production isn’t just for exercise. You are constantly producing aerobic energy. When you’re sitting down, almost all your energy is produced this way. But get this: It’s the same when you run the marathon, during which 99 percent of your energy production is aerobic. Even sprinting uses aerobic energy—up to 20 percent for the 100-meter dash.



Anaerobic energy is created within your cells without using oxygen. (This does not mean that there is no oxygen in your cells; there is always oxygen in your cells.) Anaerobic energy is produced when your body needs energy faster than your aerobic system can produce it. The problem with anaerobic energy production is that it’s short-lived, fizzling out after about a minute at full capacity. That’s perfect for activities like jumping, lifting weights, or sprinting, but not so good for long runs or sports like soccer, biking, and swimming.


Lactic acid

Lactic acid has spent almost a century serving as the boogeyman of running. Long thought to be a by-product of anaerobic energy production, lactic acid was blamed for muscle fatigue and pain during hard running. There’s now evidence, however, that lactic acid is never formed within muscles. Instead, two different substances—lactate and hydrogen ions—are created. Lactate is a fuel that muscles use to create aerobic energy. Hydrogen ions do lead to acidosis, a presumed cause of fatigue, but they aren’t a factor in longer races.



If there’s one science-y term you should know, it’s this. Mitochondria are microscopic structures within your cells that produce all your aerobic energy—and around 90 percent of the energy that you use every day. It’s mitochondria that use the oxygen you breathe. Training increases both the number and size of the mitochondria in your muscle cells. The more mitochondria you have, the more aerobic energy you can produce, allowing you to run farther faster.


Pump Up Your Running Routine

Whether you’re a miler or an ultramarathoner, Build Your Running Body offers more than 150 workouts, based on the latest research in physiology, to help runners improve their times, run longer and more comfortably, and reduce injury. Learn more about the book here.

Excerpt from Build Your Running Body: A Total-Body Fitness Plan for All Distance Runners, from Milers to Ultramarathoners—Run Farther, Faster, and Injury-Free © Pete Magill, Thomas Schwartz, and Melissa Breyer, 2014. Reprinted with permission from the publisher, The Experiment. Available wherever books are sold.

Reader's Digest
Originally Published in Reader's Digest