Reference ranges on blood tests are calculated from large population studies. The 'normal' range represents roughly the middle 95% of all people tested — which includes sedentary adults, people with undiagnosed conditions, people who rarely exercise, and people across a huge age spread. When your result falls within that range, your lab report says 'normal'. But normal for a sedentary 55-year-old is not the same as optimal for a 32-year-old who trains five days a week.
Take testosterone as an example
The standard male reference range runs from about 10 to 35 nmol/L. A result of 11 nmol/L would be flagged as 'normal' on a standard report. But most sports medicine physicians and longevity researchers would consider anything below 15–17 nmol/L to be functionally low for an active male — associated with reduced recovery, lower muscle protein synthesis, brain fog, and impaired libido. Your GP would see 11 and say fine. A performance-focused practitioner would see 11 and want to investigate.
Or consider ALT
ALT is a liver enzyme. The standard range tops out at around 56 U/L. If you lift weights four or five times a week, it's entirely normal for your ALT to sit at 60–70 U/L — because ALT is released from muscle cells when they're damaged during training, not just from the liver. A standard blood report would flag this as abnormal. A report calibrated for athletes would note it as expected and suggest retesting 72 hours post-exercise before drawing any conclusions.
Three layers of reference ranges that matter
Standard ranges — population averages. Useful for detecting serious pathology, but too broad to be meaningful for health optimisation. Athlete-adjusted ranges — recalibrated for people under significant physical training load. These account for the normal physiological adaptations that make standard ranges misleading. Optimal ranges — drawn from longevity and performance research. These represent the levels associated with the best health, cognitive, and physical outcomes — not just the absence of disease. When you upload your bloodwork to MarkerX, you can toggle between all three. You'll see not just whether you're 'in range', but whether you're actually optimised. The goal was never just to tell you what's wrong. It's to tell you how much better you could be.