Off-season November to January · Build February to April · Pre-race six to eight weeks before your A-race. Correcting most findings takes eight to twelve weeks, which is why the off-season baseline is the one that matters most.
The panel
| Test | What it tells a triathlete | When | Ask about |
|---|---|---|---|
| Ferritin, serum iron, transferrin saturation, full blood count | Iron stores and oxygen-carrying capacity. Run volume, sweat and, for women, menstruation drain the store long before hemoglobin drops; performance fades in between | OffBuildRace | Your ferritin number, not just “iron is fine.” Many sports physicians consider a level that is normal for a sedentary adult inadequate for an endurance athlete |
| Vitamin D (25-OH) | Bone, muscle and immune function. Indoor winter training lowers it; deficiency travels with stress fractures and illness days | OffBuild | Your level and whether it needs correcting before the build |
| Thyroid: TSH with free T3 and free T4 | Metabolic rate and recovery. Heavy load and under-fueling can lower free T3 while TSH stays in range | OffRace | The free hormones, not TSH alone |
| Men: total and free testosterone, SHBG, LH. Women: estradiol, progesterone, LH/FSH, plus a cycle history | Whether training load and energy availability have suppressed the reproductive axis. In both sexes this is the classic signal of relative energy deficiency in sport (RED-S) | OffRace | Whether the result is read against your training hours and your fueling, not against a sedentary reference range |
| Morning cortisol | Stress-hormone load. A high cortisol-to-testosterone pattern is a recognized overreaching signal | Race | Draw it early morning, rested, not the day after a hard session |
| hs-CRP | Inflammation. Separates normal training stress from something that is not resolving | OffRace | Draw at least 48 hours after your last hard session |
| Creatine kinase (CK) | Muscle breakdown. Useful as a trend against load, meaningless the morning after a brick | Build | Timing: 48 hours after hard work |
| Fasting glucose, fasting insulin, HbA1c | Metabolic health. A strong aerobic engine can hide poor fuel handling for years, and mid-race gut trouble sometimes starts here | Off | Fasting insulin specifically; it moves years before glucose |
| Lipid panel with ApoB | Cardiovascular risk. Endurance training does not exempt anyone, and masters athletes are the group most surprised by this result | Off | ApoB, not just LDL |
| Magnesium, B12, folate | Cramping, fatigue and red-cell production. Commonly low in high-volume athletes on restricted diets | Off | Whether your diet, not a supplement, should fix a low result |
| DEXA body composition | Lean mass, fat mass, visceral fat and bone density. Low bone density in a triathlete is a RED-S flag, not a footnote | Off | Bone density, especially if you are a woman or have had a stress fracture |
| VO2 max or lactate threshold test | Capacity and the intensities your zones should actually sit at | Off | Whether your training zones were set from a test or a formula |
Red flags: test now, not next season
- Pace or power falling for four or more weeks with consistent training
- A cycle that has become irregular or stopped since volume went up
- Waking between 2 and 4 a.m. most nights
- A stress fracture, or two in two years
- Three or more colds or illnesses in a season
- Resting heart rate up and HRV down for two weeks running
- Libido, mood or motivation gone flat with no life explanation
Bring to the visit
- Your race calendar and the A-race date
- Eight weeks of training log: hours, intensity, brick and long sessions
- Wearable export or screenshots: HRV, resting heart rate, sleep
- Every prior blood result you can find
- Your full supplement and medication list, including anything from a shop
- For women: cycle history for the last six months
- What you eat per hour on the bike and run, honestly
- The events you race and whether they are USADA-tested
Timing that makes the panel worth drawing
- Rested. No hard session for 48 hours before a draw; CK, CRP and cortisol are otherwise a picture of Tuesday’s brick, not of you.
- Fasted and early. Glucose, insulin, lipids and cortisol want a morning, fasted draw.
- Same conditions each time. A trend is only a trend if the draws are comparable.
- Twelve weeks before it matters. Iron and vitamin D take that long to correct. An off-season panel gives you the build; a pre-race panel only tells you what you are racing with.
The Season Check
Everything on this page, read by a physician who understands training load, with a written plan your coach can use. Aether Medicine, Philadelphia, PA.
Book a Season CheckFor Dr. Christian’s review before publication. The panel and its timing are written from the general sports medicine literature (IOC RED-S consensus statements; iron deficiency in endurance athletes; overreaching markers). No numeric targets are given on purpose; if you want to publish a ferritin or vitamin D target for endurance athletes, add it here with the source. Confirm the panel matches what the Season Check actually orders, and whether Aether offers IV iron, which changes the “ask about” line for ferritin.
This checklist is educational and does not constitute medical advice. Athletes subject to anti-doping rules are responsible for their own compliance and should consult their governing body before starting any medication or supplement.