Forget longevity buzzwords like Zone 2 and VO2 max, a top personal trainer says. Focus on this simple metric.

Source: Business Insider

Harley Pasternak, a celebrity trainer, has worked with clients including Rihanna. Emma McIntyre/Getty Images for Alo YogaTracking metrics like VO2 max and Zone 2 cardio is going mainstream via the longevity crowd. Harley Pasternak, a top trainer, said most of us don't need to track them to improve our health.