The reference range printed next to your result is not a target. It is a population statistic: roughly the central 95% of values from the people that lab has drawn blood from, a group that skews older, sicker, and far more sedentary than you. “Normal” means “statistically unremarkable for that population,” which is a different claim from “optimal for a person who trains five days a week.” Athletes sit outside those ranges constantly, in both directions, sometimes because something is wrong and often because training itself moved the number.
Reading your own bloodwork well means knowing which is which, and then bringing that context to a clinician instead of either panicking at a flagged value or shrugging off a real one.
What training does to your labs
Creatinine runs high in muscular people. It is a waste product of muscle metabolism, produced in proportion to how much muscle you carry. Because eGFR, the standard kidney function estimate, is computed from creatinine, a lifter’s kidneys routinely look worse on paper than they are. Run your numbers through the GFR calculator to see how the equation works, and know that cystatin C is the muscle-independent cross-check a clinician can order.
Liver enzymes and CK spike after hard sessions. AST and ALT are not liver-exclusive; skeletal muscle releases them when it is damaged, which is what hard training is. Creatine kinase can rise ten-fold after a heavy leg day and stay elevated for days. A panel drawn the morning after squats can look like liver disease in a perfectly healthy person. This is the single most common athlete bloodwork false alarm, and it is entirely avoidable by timing the draw.
Ferritin is the classic endurance deficiency. Iron losses through sweat, foot-strike hemolysis and gut losses add up, especially in runners and menstruating athletes, and low iron stores blunt aerobic adaptation long before anemia shows up in hemoglobin. The trap is that ferritin is also an inflammation marker: test during a brutal training block and inflammation can prop a genuinely low value up into the normal range. Pairing it with hs-CRP and full iron studies is how you see through that.
Hormones move with training load. Testosterone dips and cortisol climbs during periods of heavy accumulated load and under-fueling; both drift back with recovery. A single low testosterone reading in the middle of a hard block is a data point about the block at least as much as about you.
Lipids improve with training, mostly. Consistent endurance work reliably raises HDL and lowers triglycerides. But a very hard recent block, rapid weight loss, or a low-carb experiment can transiently shift LDL, which is another argument for testing in a stable, recovered window rather than mid-experiment.
The panel worth tracking over time
| Marker | Why an athlete tracks it |
|---|---|
| Ferritin + iron studies | Iron stores gate aerobic adaptation; the most common fixable endurance deficiency |
| Vitamin D | Muscle function, bone, immunity; commonly low in indoor athletes and northern winters |
| hs-CRP | Baseline inflammation, and the decoder for a falsely normal ferritin |
| Fasting glucose + HbA1c | Metabolic health over months, not one morning |
| Lipid panel | Long-run cardiovascular risk; responds to training within months |
| Thyroid (TSH, free T4) | Energy, recovery and unexplained performance drops; can shift with chronic under-fueling |
| Testosterone | Tracks accumulated training stress and fueling adequacy over time |
| CBC + metabolic panel | The basics: hemoglobin, electrolytes, kidney and liver context for everything above |
The list is deliberately boring. Exotic markers are fun, but a two-year trend line on ferritin, vitamin D and HbA1c under consistent conditions tells you more than any single deluxe panel ever will.
How to test so the numbers are comparable
- 1
Standardize the conditions
Morning, fasted 10 to 12 hours, water allowed and encouraged, since dehydration concentrates half the panel. Same conditions every single time; a trend line is only as good as its worst point.
- 2
Take 48 to 72 hours easy before the draw
No hard sessions in the 2 to 3 days before. This is what keeps AST, ALT, CK and inflammatory markers from photobombing the results. Easy walking or a genuinely light spin is fine.
- 3
Use the same lab where possible
Different labs use different assays and different reference ranges. A value that looks like it moved 15% may just have moved buildings. Same lab, same time of day, removes that noise.
- 4
Track trends, not single values
One flagged result is a question, not a conclusion. Your ferritin going 60, 45, 31 over a year of increasing mileage is a story worth acting on even though every value passed the lab’s floor; a single 31 in isolation is nearly uninterpretable.
- 5
Bring the training context to your doctor
Tell them what you lift, how much you run, and when your last hard session was. A creatinine of 1.4 means something different in a 90 kg lifter than in a sedentary patient, and your clinician can only make that adjustment if they know which one you are.
The mindset that makes bloodwork useful
Treat your blood like you treat your training log: a longitudinal record of you versus you, sampled under repeatable conditions, interpreted with context. The lab’s range answers “is this person statistically unusual?” Your trend line, read together with a clinician who knows you train, answers the question you actually care about: is my body absorbing this training, or quietly paying for it.