The value of CrossFit for runners has been hotly debated the past couple of years. Is CrossFit a good supplement to running? A replacement for running? A small study conducted in Alabama provides some useful real-world information on what happens physiologically during a CrossFit workout.

Nine adults who had been doing regular CrossFit sessions for at least three months did a popular CrossFit workout known as "Cindy." It consists of doing a set of 5 pull-ups, 10 push-ups, and 15 air squats, and repeating that set as many times as possible within 20 minutes.

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During the workout, the exercisers reached an average intensity of 63% of VO2max, a measure of aerobic output. The American College of Sports Medicine classifies workouts done at an intensity between 64% and 90% of VO2max as "vigorous intensity." In running terms, working out at around 65% of VO2max corresponds with steady running, neither a jog nor a harder effort like a tempo run or track workout.

During the 20-minute workout, the exercisers burned an average of 260 calories. Using the general guideline of 100 calories burned per mile, this roughly corresponds to running 2.5 miles in 20 minutes, or averaging 8:00 per mile for 20 minutes.

This study suggests that this CrossFit workout gives reasonably fit adults who are accustomed to that mode of training a decent 20-minute workout.

That's not the same, however, as saying that it's equivalent to a steady 20-minute run. If you're training to run faster, the specificity of your workouts becomes more important than for people aiming for general fitness. If you're one such runner, consider workouts like the above CrossFit session more a supplement to your running than a replacement.

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In addition, as Runner's World editor-at-large Amby Burfootpointed out earlier this week, impressive-looking calorie-burning totals for short, high-intensity workouts need to be put in context. You might burn more calories doing 20 minutes of intense CrossFit work than in running easily for 20 minutes, but you can probably burn more total calories from easy running, simply because you can sustain the activity for longer.

The study's findings will be presented later this month at the annual meeting of the American College of Sports Medicine.

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Scott Douglas Scott is a veteran running, fitness, and health journalist who has held senior editorial positions at Runner’s World and Running Times.

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