Blood Work for Athletes: What to Test, How to Read It, and Why Your Wearable Can't Tell You This

Your Whoop knows your HRV. Your Garmin tracks your VO2 max. Your Apple Watch counts every step. But none of them can tell you why your recovery scores tanked for three weeks straight, or why you cannot put on muscle despite training harder than ever.

Blood work can.

It is the one layer of data your wearable physically cannot measure. And for athletes over 30, it is arguably the most important layer you are ignoring.

The gap in your data stack

Wearables are surface sensors. They read what your body is doing right now. Heart rate. Motion. Skin temperature. Sleep stages. They are reactive tools. They report symptoms.

Blood markers tell you why those symptoms exist. Low HRV for two weeks? Could be overtraining. Could also be low iron, tanked Vitamin D, or subclinical thyroid dysfunction. Your wearable cannot distinguish between those. A blood panel can.

This is especially true for athletes over 40. Hormonal shifts, slower recovery, and nutrient absorption changes mean the gap between “clinically normal” and “optimal for performance” widens every year. Your GP might look at your testosterone result and say “that’s within range.” An athlete looking at the same number through a performance lens might see a reason they are losing muscle despite doing everything right.

What to actually test

Not every blood panel is useful for athletes. The standard panel your GP orders for a check-up is designed to catch disease, not optimise performance. Here is what matters:

Hormones

Free testosterone is the one most athletes over 40 should start with. Total testosterone gets the headlines, but free testosterone is what your muscles actually use. It is the unbound fraction circulating in your bloodstream, available for tissue repair and protein synthesis. If your total T is “normal” but your free T is low, you have your answer for why recovery feels harder than it used to.

SHBG (sex hormone binding globulin) binds testosterone and makes it unavailable. High SHBG with normal total T equals functionally low testosterone. This is common in endurance athletes.

Cortisol tells you about your stress load. Chronically elevated cortisol breaks down muscle, disrupts sleep, and blunts testosterone production. If you are training hard, working full time, and sleeping badly, cortisol is probably the number you need to see first.

Vitamins and minerals

Vitamin D is the single most common deficiency in athletes. Low Vitamin D correlates with lower power output, slower recovery, weaker bone density, and even reduced grey matter volume in the brain (per recent RCT data). If you train indoors in the morning and work from home, you are almost certainly not getting enough sun. Test it. Supplementing 2000 to 4000 IU daily is cheap and effective.

Ferritin (iron stores) is critical for oxygen transport. Low ferritin tanks your endurance before it shows up as clinical anaemia. Female athletes and heavy sweaters are especially vulnerable. If your easy runs feel inexplicably hard, this might be why.

Vitamin B12 and folate support red blood cell production and neurological function. Deficiency causes fatigue that mimics overtraining.

Metabolic markers

HbA1c gives you a 90-day average of blood glucose management. For athletes interested in body composition, this tells you more about your metabolic health than any single fasting glucose reading.

Insulin alongside glucose gives a clearer picture of insulin sensitivity. You can have normal glucose and elevated insulin for years before anything shows up on a standard test.

Inflammation

hs-CRP (high-sensitivity C-reactive protein) is a general inflammation marker. In athletes, chronically elevated hs-CRP can indicate overtraining, poor recovery, or an underlying issue that wearable data alone will never surface.

Lipids

The standard panel (total cholesterol, LDL, HDL, triglycerides) still matters, especially when combined with ApoB which is increasingly considered the best single predictor of cardiovascular risk. Endurance athletes sometimes have paradoxically poor lipid profiles despite being “fit.” Worth checking.

Thyroid

TSH, free T3, and free T4 round out the picture. Subclinical hypothyroidism causes fatigue, weight gain, and cold intolerance that looks exactly like overtraining. Common in women, underdiagnosed in men.

“Normal” is not optimal

This is the critical distinction. Clinical reference ranges on your pathology report are set to catch disease. They define the range where 95% of the general population falls. That population includes sedentary 70-year-olds and teenagers.

If you are training six days a week and trying to perform at your best, “normal” is not your benchmark. You want to know where you sit within that range and whether the number supports what you are trying to do.

Vitamin D at 52 nmol/L is “within range.” Most labs set the lower bound at 50. But performance-focused clinicians target 100 to 150 nmol/L. At 52, you are technically fine. Functionally, you are leaving recovery and bone density on the table.

Free testosterone at the bottom of the reference range might not trigger a flag from your GP, but it explains why you are losing muscle mass at 48 despite hitting the gym five days a week.

How often to test

For most athletes, twice a year is the sweet spot. Once at the start of a training block (baseline) and once mid-season or after a significant change in training load.

If you find something out of range and start supplementing or making changes, retest that specific marker at 8 to 12 weeks to see if the intervention is working.

More frequent than that is unnecessary unless you are managing a specific condition.

What P247 does with your blood work

This is where the data stack comes together.

P247 can now read your blood panel directly. Snap a photo of your pathology results or upload the PDF. The system extracts every marker, flags anything out of range, and gives you a plain-English summary of what matters and what to do about it.

But the real value is not in reading one panel. It is in connecting blood work to everything else. Your wearable data shows you that recovery has been poor for three weeks. Your blood panel shows your Vitamin D is at 48 and your ferritin is borderline. Now you have the full picture. Now you can actually fix it instead of guessing.

Over time, as you upload more panels, you can track trends for any marker. Watch your Vitamin D climb after supplementation. See your testosterone respond to better sleep. Connect the lines between what your blood says and what your wearable shows.

That is the layer nobody else is building.

Getting started

1. Ask your GP for a “comprehensive blood panel” and specifically request free testosterone, Vitamin D, ferritin, hs-CRP, full thyroid (TSH, free T3, free T4), and HbA1c. Most GPs will order these without pushback if you explain you are tracking athletic performance.
2. Get the results (usually 2 to 5 business days).
3. Open P247, go to Data, tap Blood Work, and scan the results with your camera or upload the PDF.
4. Read the summary, check the flagged markers, and follow the recommended action.

That is it. Five minutes to close the biggest gap in your data stack.