This test might be the best way to track fitness and longevity

FITNESS is full of numbers meant to help you become faster and stronger. There’s your mile run time, your resting heart rate and measures of strength and flexibility. But perhaps the gold standard is VO2 max.

A handful of years ago, the test – which tracks how much oxygen your body absorbs – was an obscure tool mainly used by elite athletes. Today, it’s touted by fitness professionals and wellness experts like Peter Attia as being a useful measure for all exercisers.

But getting an accurate number requires an expensive and exhausting lab evaluation. And estimates provided by wearable devices might not tell you much. So how useful is it to invest time and money in the full work-up, and how important is knowing your VO2 max?