Trail Tips

Should You Celebrate Your Watch’s V02 Max Numbers?

Are the watch estimates correct? And how much do they matter?

Lock Icon

Become a member to unlock this story and receive other great perks.

Already have an Outside Account? Sign in

Outside+ Logo

All Access
15% off New Year Sale
$7.02 / month*

  • A $500 value with everything in the Print + Digital Plan plus 25+ benefits including:
  • Member-only content on all 17 publications in the Outside network like Outside, SKI, Backpacker, Clean Eating, and more
  • Today’s Plan training platform with customized programs
  • Gaia GPS Premium with hundreds of maps and global trail recommendations, a $39.99 value
  • Download your personal race photos from FinisherPix* for one race (up to a $100 value).
  • Get up to $30 off your next race and $30 off race fees every year you are a member through AthleteReg*
  • Exclusive discounts on gear, travel, and more
  • Annual subscription to Outside magazine
Join Outside+
Trail Runner Magazine

Print + Digital
50% Off New Year Sale
$2.00 / month*

  • Annual subscription to Trail Runner magazine
  • Access to all member-exclusive content on TrailRunnerMag.com
  • Ad-free access to TrailRunnerMag.com
Join Trail Runner

*Outside memberships are billed annually. Print subscriptions available to U.S. residents only. You may cancel your membership at anytime, but no refunds will be issued for payments already made. Upon cancellation, you will have access to your membership through the end of your paid year. More Details

My watch just gave me an updated VO2 max number—should I celebrate?

—Gruia, San Jose, California

VO2 max for a runner is similar to the distance a golfer can hit on the driving range. It’s a component of success, but it’s not the whole story. No matter what, never put too much stock in a single metric related to your running fitness (or anything else). Life is always more complex than that.

Are the watch estimates correct? First, it’s helpful to think about what VO2 max is: maximum aerobic capacity, corresponding to the oxygen uptake peak during a period of intense exercise (usually an effort an athlete can sustain for 7 to 11 minutes, but with individual variance). Your watch is not directly measuring oxygen uptake, instead it’s approximating how much oxygen it thinks you use based on heart rate, pace, weight and other variables. It’s kind of like using a shadow of a tree to tell you how tall the tree is. That may work, but you need to have precise input variables like the angle of the sun and distance to the tree. Even then there may be some variance from actually measuring the tree.

RELATED: What You Need to Know About VO2 Max

Studies indicate that the shadow-drawings might not be that accurate. Three presentations summarized in the Medicine & Science in Sport and Exercise journal found statistically significant differences between watch VO2 max predictions and actual VO2 max. Some over-predicted, some under-predicted, some did both. Accuracy is further diminished if using optical wrist sensors rather than chest straps, which studies indicate are not fully reliable to measure heart rate across the population.

When thinking about what your watch is telling you, remember the old saying: “even a broken clock is right twice a day.” On top of that, even if the VO2 max number is correct, there’s no reason for it to inform your training approach. Training based on VO2 max changes is largely ineffective since VO2 max is primarily a genetic variable with most significant changes taking place when an athlete starts out. After that, further improvements are explained by other variables like running economy.

RELATED: The Body Doesn’t Know Miles, It Knows Stress

In conclusion, I fully support celebrating if your watch is telling you a fun story you want to hear. We can all use more celebration in our lives. But if the watch is being a jerk, assume that it’s a stupid, inaccurate jerk and pay attention to other performance metrics like changes in effort and increased joy while running uphill.

David Roche partners with runners of all abilities through his coaching service, Some Work, All Play. With Megan Roche, M.D., he hosts the Some Work, All Play podcast on running (and other things), and they wrote a book called The Happy Runner.