The Tune-Up
Your bike gets a tune-up at the end of the season. Your body deserves the same.
A baseline blood panel is that tune-up, and the off-season is the right window for it. You’re rested, training is light, and if something’s off, there’s time to fix it.
Two markers worth asking your doctor about:
Ferritin (your iron stores). It often runs low in endurance athletes, especially women.
Vitamin D. It slides through the winter. North of about 35° latitude, roughly a line from Memphis to Charlotte, the winter sun is too weak to make much of it.
Deficiencies can pass for “just tired.”
Baseline is the key word. Lab ranges are built from the general population, and trained bodies don’t always fit them. Endurance training expands your plasma volume, which can make hemoglobin read low. A hard ride can push muscle enzymes above “normal” for days. Neither is necessarily a problem, but you only know that if you know what normal looks like for you.
Now the trap. Reference ranges are drawn around the middle 95% of healthy people. Run a 20-marker panel, and the odds that at least one number comes back flagged are roughly two in three, even if you’re healthy. More markers don’t mean more answers, either. In one study of 50 elite athletes complaining of fatigue, a standard blood panel changed the doctor’s diagnosis in just one case.
A flagged number can become an obsession: the new supplement, the retest, the diet overhaul, the retest after that, all chasing a marker that may never have mattered. Better numbers don’t automatically make a healthier rider.
A few tips:
Test rested. Go in the morning, well hydrated. Skip hard or long rides the day before, and skip heavy lifting for two or three days.
Don’t supplement first. Starting iron or vitamin D before you test muddies the baseline, and too much of either can do harm.
Interpret results with your doctor. A forum and an AI chatbot are the wrong places for this.
Retest when something changes, like unexplained fatigue or a stalled season.
Get the baseline, then double down on the fundamentals: sleep, good food, consistent training.
See you next week,
Steve
Explore more
Blood Work for Cyclists: Why You Need It (PezCycling News). A sports dietitian’s guide to iron, vitamin D and timing your test.
Blood Tests for Cyclists: Which Tests Actually Matter? (Roadman Cycling). The case for testing with a question in mind.
How Coaches Can Use Blood Testing for Better Endurance Training (TrainingPeaks). Iron, vitamins and how often to retest.
Are You Iron Deficient? Are You Sure? (Dr. Stacy Sims). Why active women are at higher risk, and what to know before supplementing.