If you’ve been getting more serious about running, you’ve probably heard the term “VO2 max” thrown around. “VO2 max is a tested value of aerobic capacity,” says Dr. Jamey Plunk, an endurance athlete and professor of exercise and sport science at the University of Mary Hardin-Baylor. “If a runner wants to run faster aerobically, he must increase his VO2 max. VO2 max is not a reflection of a runner’s sprint speed, but endurance speed.” And since running faster, for longer, is pretty much the goal for endurance athletes, VO2 max is the key to becoming a better distance runner. The good news is, it’s not rocket science—a little hard work and well-executed training can do the trick, and might just earn you your next PR.
A Crash Course on VO2 Max
Essentially, the higher your VO2 max, the more efficiently your heart and lungs deliver oxygenated blood to your working muscles, and the more efficiently you’re able to extract that oxygen to generate fuel for movement. If your VO2 max is poor, it won’t take long before your lungs and legs start to burn and you reach your anaerobic threshold. According to Plunk, that’s the point where you no longer have enough oxygen to continue pushing yourself at the same speed or intensity. Inevitably, you’ll have to slow down to catch your breath.
On the other hand, if you have an excellent VO2 max, you can sustain faster speeds for longer, or slightly slower speeds for much longer. You’re a more efficient aerobic athlete, which ultimately pays off in an endurance race. “In events lasting longer than two hours, like a marathon, you’re able to run faster while relying primarily on fats as fuel rather than carbs,” Plunk says.
Why Burning Fat Instead of Carbs Matters
The higher the percentage of your VO2 max that you reach during training or an event, the more you rely on carbohydrates—specifically, glycogen—as a fuel source to sustain exercise. And because glycogen is a limited fuel source—Plunk says stores last only about two hours without in-race supplementation—when you run out, you “bonk,” or hit the proverbial wall, and have no choice but to slow substantially.
Fat, on the other hand, is different. “Fat is virtually an unlimited fuel source,” Plunk says. “So in theory, if you increase your VO2 max, you can run at the same pace as before while using mostly fat as your fuel source instead of carbohydrates, enabling you to run much longer without hitting the wall. Or, you can run faster while still running at a lower percentage of your VO2 max.” In other words, if you’re a half-marathon runner, improving your VO2 max would enable you to run the same half-marathon distance at a faster pace with improved performance, or would help you run even farther while maintaining your typical half-marathon speed. It’s a clear improvement in running and nutrient economy.
How to Train
“Intervals are by far the most efficient way to increase your VO2 max,” Plunk says. “Could be fartlek runs [more on that later], tempo runs, track intervals, or even hill repeats.” That said, there are a few rules to abide by:
- Each individual effort needs to last a minimum of two minutes—this is the point at which the aerobic system “takes over” from the anaerobic system. If you want to improve your aerobic capacity, you need to train your aerobic system. Super-short intervals, such as 100-meter dashes followed by rest, won’t do the trick.
- For faster gains in VO2 max, you need to increase the intensity of your intervals.
- Limit interval training workouts to two workouts per week.
Try Fartlek Training
Fartlek training is one of the most natural ways to put interval training to work because it’s less structured. Fartlek means “speed play” in Swedish, and it’s essentially a way to incorporate intervals into a longer training run, where throughout your run you vary your pace between faster and slower speeds. For instance, you might run a block as fast as you can, then slow to a jog until you feel recovered before picking your pace back up again.
As an alternative, you could time your intervals, jogging for a minute, running for a minute, then sprinting as long as you can before slowing back down to a more-sustainable jog. You continue to tax your aerobic system because you never stop to rest completely, but you continuously test your anaerobic threshold by increasing your intensity to the level of your threshold, then decreasing it to a sustainable intensity. Thirty to 40 minutes of this type of speed play can do wonders for your VO2 max.
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