BPR
Blood tests by group

Blood tests for endurance: running, cycling, swimming

Long hours of training change your iron, your vitamin D and how you recover. A few markers, compared with your own baseline, show where you stand.

See the testsDownload the guide (PDF)
A woman tying her trainers in a park before a run

Why it makes sense at this stage

What the research supports, with the source of each point at the bottom of the page.

  1. 01

    Low iron is the most common problem in endurance sport, and it comes before anaemia

    About 15 to 35% of female and 5 to 11% of male athletes are low in iron. In elite runners and triathletes followed for six years, 60% of the female triathletes had at least one episode. Ferritin shows your stores.[1, 2, 3]

  2. 02

    Endurance training itself moves your iron

    Exercise loses iron through sweat, the gut, the urine and the breakdown of red cells. The inflammation after hard sessions raises hepcidin, a hormone that cuts how much iron you absorb.[4]

  3. 03

    Not eating enough for your training shows in the blood

    The IOC lists low T3, low testosterone in men and raised cholesterol among the signs of not eating enough for your training. Endurance is the sport where training volume weighs most.[5, 6]

  4. 04

    UK winters and indoor training lower vitamin D

    In a review of 2,313 athletes, 56% had low vitamin D; the risk was higher in the UK, in winter and early spring, and in indoor sport, such as pool swimming. In a UK study, 62% of professional athletes not taking supplements were under 50 nmol/L in winter.[7, 8]

  5. 05

    In cycling, urea follows training load better than CK

    In simulated training camps, cycling fatigue showed in urea, while CK was the marker for strength and team sport. Both only mean something against your own baseline.[9, 10]

The tests and why

What usually makes sense for this group. Your GP can tell you what fits your own case.

Ferritin, with iron and transferrin saturation

Your iron stores. Iron deficiency is common in endurance athletes and can be there before haemoglobin falls.[1, 2, 3, 4]

When to repeat: About twice a year, and before a big training block or altitude; after treatment, as your GP advises.

Full blood count

Haemoglobin and red cells. Training expands blood plasma, so haemoglobin can read slightly low in trained athletes without true anaemia.[3, 11]

When to repeat: With your ferritin.

High-sensitivity CRP

Inflammation. A long race or a hard session raises it for a short time and can push ferritin up, so it helps read your iron result.[12, 13]

When to repeat: With your ferritin.

Vitamin D, 25(OH)D

Your vitamin D level. Winter, early spring and indoor training, such as pool swimming, raise the chance of a low result.[7, 8, 14, 15]

When to repeat: Late autumn or winter; after supplements, as your GP advises.

Urea and CK

Load and recovery. In endurance training urea follows fatigue best; both only mean something against your own baseline.[9, 10, 16]

When to repeat: As a series, at the same time of day and the same point in your training week.

Free T3, testosterone (men) and cholesterol

The IOC lists low T3, low testosterone in men and raised cholesterol among the signs of not eating enough for your training. No single test confirms it; the pattern is something to take to your GP.[5, 6]

When to repeat: If you have signs such as tiredness, falling performance, a bone stress injury or missed periods, as your GP advises.

B12 and folate (vegan, vegetarian or restrictive diet)

Vegan and vegetarian diets, or cutting out food groups, raise the risk of low B12.[17]

When to repeat: If your diet changes, or as your GP advises.

What a blood test can and cannot do

It can

  • Show your iron stores before haemoglobin falls
  • Show your vitamin D after winter and indoor training
  • Give you a baseline to compare each training block with

It cannot

  • Find or rule out REDs or overtraining: no single test does that
  • Make you faster: raising ferritin helped only when it was very low
  • Decide on iron tablets: that is your GP's call, after a measured deficiency

Tests that cover these markers

Not sure which one? The guided check-up suggests a starting point in a few questions.

Find your check-up

Prices are in the app, once you have an account.

What to do with your result

Your result arrives in your account, with reference ranges. A value outside the range, or a symptom with a normal result, is a conversation with your GP: treatment and supplements are their call. Repeat the same test later to compare.

Take the guide with you

The reasons, the tests and every reference, in a few pages. Free to download, no email needed.

Guide in English (PDF) Guide in Portuguese (PDF)

See also

References

  1. 1.Sim M, Garvican-Lewis LA, Cox GR, et al. Iron considerations for the athlete: a narrative review. Eur J Appl Physiol. 2019;119:1463-1478. doi:10.1007/s00421-019-04157-y PMID 31055680.
  2. 2.Coates A, Mountjoy M, Burr J. Incidence of Iron Deficiency and Iron Deficient Anemia in Elite Runners and Triathletes. Clin J Sport Med. 2017;27:493-498. doi:10.1097/JSM.0000000000000390 PMID 27606953.
  3. 3.Clénin G, Cordes M, Huber A, et al. Iron deficiency in sports - definition, influence on performance and therapy. Swiss Med Wkly. 2015;145:w14196. doi:10.4414/smw.2015.14196 PMID 26512429.
  4. 4.Peeling P, Dawson B, Goodman C, Landers G, Trinder D. Athletic induced iron deficiency: new insights into the role of inflammation, cytokines and hormones. Eur J Appl Physiol. 2008;103:381-391. doi:10.1007/s00421-008-0726-6 PMID 18365240.
  5. 5.Mountjoy M, Ackerman KE, Bailey DM, et al. 2023 International Olympic Committee's (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs). Br J Sports Med. 2023;57:1073-1097. doi:10.1136/bjsports-2023-106994 PMID 37752011.
  6. 6.Stellingwerff T, Mountjoy M, McCluskey WT, et al. Review of the scientific rationale, development and validation of the International Olympic Committee Relative Energy Deficiency in Sport Clinical Assessment Tool: V.2 (IOC REDs CAT2). Br J Sports Med. 2023;57:1109-1118. doi:10.1136/bjsports-2023-106914 PMID 37752002.
  7. 7.Farrokhyar F, Tabasinejad R, Dao D, et al. Prevalence of vitamin D inadequacy in athletes: a systematic-review and meta-analysis. Sports Med. 2015;45:365-378. doi:10.1007/s40279-014-0267-6 PMID 25277808.
  8. 8.Close GL, Russell J, Cobley JN, et al. Assessment of vitamin D concentration in non-supplemented professional athletes and healthy adults during the winter months in the UK: implications for skeletal muscle function. J Sports Sci. 2013;31:344-353. doi:10.1080/02640414.2012.733822 PMID 23083379.
  9. 9.Hecksteden A, Skorski S, Schwindling S, et al. Blood-Borne Markers of Fatigue in Competitive Athletes - Results from Simulated Training Camps. PLoS One. 2016;11:e0148810. doi:10.1371/journal.pone.0148810 PMID 26891051.
  10. 10.Hecksteden A, Pitsch W, Julian R, et al. A New Method to Individualize Monitoring of Muscle Recovery in Athletes. Int J Sports Physiol Perform. 2017;12:1137-1142. doi:10.1123/ijspp.2016-0120 PMID 27967274.
  11. 11.Mairbäurl H. Red blood cells in sports: effects of exercise and training on oxygen supply by red blood cells. Front Physiol. 2013;4:332. doi:10.3389/fphys.2013.00332 PMID 24273518.
  12. 12.Kasapis C, Thompson PD. The effects of physical activity on serum C-reactive protein and inflammatory markers: a systematic review. J Am Coll Cardiol. 2005;45:1563-1569. doi:10.1016/j.jacc.2004.12.077 PMID 15893167.
  13. 13.Pedlar CR, Brugnara C, Bruinvels G, Burden R. Iron balance and iron supplementation for the female athlete: A practical approach. Eur J Sport Sci. 2018;18:295-305. doi:10.1080/17461391.2017.1416178 PMID 29280410.
  14. 14.Scientific Advisory Committee on Nutrition. Vitamin D and Health. Public Health England. 2016. www.gov.uk/government/publications/sacn-vitamin-d-and-health-report
  15. 15.Farrokhyar F, Sivakumar G, Savage K, et al. Effects of Vitamin D Supplementation on Serum 25-Hydroxyvitamin D Concentrations and Physical Performance in Athletes: A Systematic Review and Meta-analysis of Randomized Controlled Trials. Sports Med. 2017;47:2323-2339. doi:10.1007/s40279-017-0749-4 PMID 28577257.
  16. 16.Haller N, Behringer M, Reichel T, et al. Blood-Based Biomarkers for Managing Workload in Athletes: Considerations and Recommendations for Evidence-Based Use of Established Biomarkers. Sports Med. 2023;53:1315-1333. doi:10.1007/s40279-023-01836-x PMID 37204619.
  17. 17.Rogerson D. Vegan diets: practical advice for athletes and exercisers. J Int Soc Sports Nutr. 2017;14:36. doi:10.1186/s12970-017-0192-9 PMID 28924423.

General information, not personal medical advice. Talk to your GP about your own situation. Questions: write to [email protected] or message us in the app.