Lab Work for Athletes: What PTs Should Care About
Dec 1
A few weeks ago, an athlete came to me frustrated.
Training was dialed. Nutrition was solid. Sleep—on point.
But performance? Flat. Slow recovery, lingering soreness, random fatigue.
He’d already seen his doctor. “My labs are normal,” he said.
Here’s the thing: normal doesn’t always mean optimal.
Especially for athletes.
When you’re pushing your body to adapt, recover, and perform, you’re playing at the edges of physiology. A “normal” lab range (built around the average sedentary person) isn’t necessarily the range that supports peak performance.
So, what do I actually care about when I look at lab work as a performance physical therapist?
1. Ferritin — The Oxygen Carrier’s Best Friend
Ferritin reflects how much iron your body has stored. Even if your hemoglobin looks fine, low ferritin can tank your endurance and recovery.
A study in the Journal of Sports Science & Medicine (2019) found that athletes with ferritin below 30 ng/mL reported more fatigue and slower adaptation to training, even when other labs were “normal.”
Low ferritin = low oxygen efficiency = sluggish sessions.
What to look for:
Men: ideally 50–150 ng/mL
Women: ideally 40–100 ng/mL
If it’s below 30, it’s time to dig deeper.
2. Vitamin D — The Silent Performance Hormone
We think of vitamin D as a “bone vitamin,” but it’s really a hormone that affects muscle recovery, inflammation, and even injury risk.
A review in Sports Health (2020) showed that athletes with vitamin D insufficiency (<30 ng/mL) had higher rates of muscle strain and stress fractures.
Here in South Florida, that surprises people—sun everywhere, right? But most of my athletes train early or late, wear sunscreen, and don’t actually get consistent UV exposure.
3. Testosterone and Cortisol — The Recovery Ratio
Testosterone helps rebuild tissue. Cortisol breaks it down. It’s not about chasing “high T” or “low cortisol”—it’s about balance.
When cortisol stays elevated (from stress, underfueling, or overtraining), even perfect rehab plans stall. You can’t build when your body thinks it’s surviving.
A study in the Journal of Strength and Conditioning Research (2021) found that an imbalanced T:C ratio correlated with slower muscular recovery and decreased training output.
4. B12 and Folate — The Energy Producers
Low B12 or folate means sluggish red blood cell production, which means sluggish oxygen delivery. Vegans, vegetarians, and endurance athletes are especially at risk.
You’ll often see “normal” ranges of B12 above 200 pg/mL—but for optimal performance, aim for >500 pg/mL.
5. Inflammation Markers — The Hidden Drain
High-sensitivity CRP (C-reactive protein) tells you how inflamed your system is.
Chronic inflammation—even mild—can delay tissue repair and blunt training gains (Frontiers in Physiology, 2021).
The Big Picture
When labs come back “normal,” don’t stop there.
Look for patterns—how recovery, mood, sleep, and soreness align with what’s on paper.
Because performance isn’t about being in range.
It’s about being in rhythm.
Takeaway:
If you’re training hard but not recovering well, your answer might not be in your program—it might be in your bloodwork. Ask your PT or doctor to look beyond normal.
References:
Dellavalle, D. M., & Haas, J. D. (2019). Iron status in athletes: Effect of diet and training. Journal of Sports Science & Medicine, 18(1), 97–106.
Owens, D. J., et al. (2020). Vitamin D and the athlete: Current perspectives and new challenges. Sports Health, 12(5), 451–458.
Hackney, A. C., et al. (2021). Hormonal regulation and training adaptation in athletes. Journal of Strength and Conditioning Research, 35(9), 2468–2477.
Martens, P., et al. (2021). Inflammation and recovery in athletes. Frontiers in Physiology, 12, 720–732.
Woolf, K., et al. (2018). Nutritional deficiencies and performance: The role of B vitamins.Current Sports Medicine Reports, 17(5), 172–178.