When not chasing PRs, I often think about how to help endurance athletes build bodies that perform and last. Endurance training is one of the most powerful longevity interventions, but only if your metabolic foundation supports the demand. Here's the essential biomarkers that I would recommend endurance athletes testing 1-2x per year for tracking their long-term health.

The Non-Negotiables:

Complete Blood Count (CBC)
This is your baseline hematological profile; it screens for anemia and early nutrient deficiencies. Here is a great article on how to interpret your CBC results as a runner.
Iron Panel ⚡

Ferritin
Serum iron
TIBC/transferrin
Transferrin saturation

Iron deficiency hits ~12% of athletes and decreases VO2max before anemia even appears. It's the #1 nutritional deficiency in the US, according to this article.

Iron can be a double-edged sword (i.e. too much iron can cause toxicity), so instead of jumping right into supplementation, it's good to talk with your doctor to find the cause and increase intake of iron through diet first.

Hack: Add high-sensitivity C-Reactive Protein (hs-CRP) to the same draw. Ferritin can rise with inflammation, so you need hs-CRP to interpret it correctly.

Comprehensive Metabolic Panel
Kidney function, liver enzymes, electrolytes. Essential for anyone in chronic training stress.
Vitamin D (25-OH)
Critical for bone health, immunity, recovery and even mood. Test this if you train mostly indoors, live at high latitude (lacking sunlight), or have darker skin.

Optional but nice to have:

Lipid panel
HbA1c / fasting glucose
Thyroid panel (TSH, free T3, free T4)
B12 + folate
DEXA scan (for bone density)

For Female Athletes:

Track menstrual regularity, libido, energy, and symptoms; don't ignore any red flags. Remember that hormonal optimization = performance optimization 💚