What are DEXA, VO2 max and RMR tests?

A plain-English guide to the three most popular body and fitness tests and what you get for the money.

DEXA (DXA) body composition scan

DEXA stands for dual-energy X-ray absorptiometry. You lie on an open table for roughly 7–10 minutes while a low-dose X-ray arm passes over you. The scan separates your weight into fat mass, lean (muscle) mass and bone, region by region (arms, legs, trunk), and most providers also estimate visceral fat, the fat around your organs. People use it to track fat loss vs. muscle loss, for example during a cut, a training block or GLP-1 weight-loss medication.

• Radiation: very low. Providers commonly compare it to a fraction of a day's natural background radiation.
• Prep: usually no exercise beforehand, light fasting, metal-free clothes.
• Body composition vs. bone density: a fitness "body comp" DEXA is not the same as a diagnostic hip/spine bone-density exam. If you need an osteoporosis assessment, ask your doctor.

VO2 max test

A VO2 max test measures the maximum amount of oxygen your body can use during hard exercise. You wear a mask while running on a treadmill or riding a bike as the intensity ramps up, typically for 8–15 minutes. Results include your VO2 max (ml/kg/min), your aerobic and anaerobic thresholds, and personalised heart-rate training zones. VO2 max is one of the strongest fitness markers linked to long-term health.

RMR (resting metabolic rate) test

An RMR test measures how many calories you burn at rest by analysing your breath while you sit or lie quietly for 10–20 minutes, usually after fasting. Instead of guessing from an online formula, you get a measured baseline for planning nutrition, plus (on many machines) whether you're burning mostly fat or carbohydrate at rest.

What should I pay?

See our DEXA, VO2 max and RMR price indexes. Bundles of two or three tests in one visit are often 10–25% cheaper than booking separately, and many labs offer first-visit discounts.