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.
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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.
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.