Training tells you what your body can do today.
Blood work gives you more information about what may be affecting that performance underneath: oxygen delivery, glucose control, organ function, inflammation, nutrient status and hormones.
It isn’t a replacement for good training, sensible nutrition or enough sleep. It is another source of useful information.
You do not need to chase every possible test. You need the right markers, taken for a reason, then interpreted properly.
1. Start with the basic picture
A sensible blood panel can help identify issues that are easy to mistake for poor motivation or inadequate training.
Persistent fatigue may be linked to poor sleep. It may also involve iron deficiency, thyroid dysfunction, anaemia, uncontrolled blood glucose or another health issue.
Poor recovery may be a programming problem. It may also be affected by low energy availability, inflammation, illness or an underlying medical condition.
Blood work does not explain everything. It can help reduce guesswork.
Here is the short version.
| Marker | Broadly helps assess | Why it may matter for training, recovery or general health |
|---|---|---|
| Full blood count | Red blood cells, haemoglobin, white blood cells, platelets | Can add context to fatigue, breathlessness, illness, recovery or unexplained drops in performance |
| Lipids | Cholesterol and triglycerides | Useful for long-term cardiovascular health, even when day-to-day training feels normal |
| HbA1c / glucose | Blood glucose regulation over time or at a single point | Can affect energy, appetite, body composition and consistency across training sessions |
| Iron / ferritin | Iron status and stored iron | Relevant to oxygen transport, fatigue, concentration, exercise tolerance and recovery |
| Thyroid | Metabolic regulation and energy use | Can help explain persistent fatigue, feeling cold, slower recovery or reduced exercise tolerance |
| Testosterone | Hormonal status linked to muscle, libido, wellbeing and red blood cell production | May affect training response and general wellbeing, but still needs proper clinical interpretation |
| Vitamin D | Bone health, muscle function, immune support | Can matter for general health, training tolerance and injury risk where deficiency is significant |
| hs-CRP | Inflammation signal | Can support wider health and cardiovascular risk discussions, but is only useful in context |
| Kidney function | Fluid balance, waste removal, electrolytes | Relevant to hydration, medication use, supplement use and overall recovery support |
| Liver function | Markers involved in nutrient processing, metabolism and general organ function | Useful when considering training load, alcohol intake, medication, supplements and overall health |
This table is a guide, not a diagnosis. It helps you see what each marker is broadly used for. It does not replace a clinician’s interpretation.
The NHS overview of blood tests explains that different tests are used to check general health, investigate symptoms and monitor existing conditions. That is the useful starting point.
2. Full blood count: oxygen, immunity and fatigue
A full blood count, or FBC, measures several types of blood cells.
The key markers include:
- Haemoglobin and red blood cell measures.
- White blood cells.
- Platelets.
- Red blood cell size and related indices.
Haemoglobin carries oxygen from your lungs to your working muscles. During training, your muscles need oxygen to produce energy, particularly during longer sets, conditioning work and repeated efforts.
If haemoglobin is low, you may notice fatigue, breathlessness, poor exercise tolerance or a higher perceived effort. Iron deficiency is one possible cause, although there are others.
White blood cells are part of the immune system. Abnormal results may reflect infection, inflammation, medication effects or other conditions. Platelets are involved in blood clotting.
This is not a performance score. A high red blood cell count is not automatically better, and a small change may reflect hydration, altitude, training status or individual variation.
The practical point is simple: if your energy has changed without a clear reason, an FBC can be part of a proper investigation.
3. Lipids: cardiovascular health matters to training
A lipid profile usually includes total cholesterol, HDL cholesterol, non-HDL or LDL cholesterol and triglycerides.
Cholesterol has important functions. Your body uses it to build cell membranes and make certain hormones. The issue is not whether you have cholesterol. The issue is the amount and type of lipoproteins carrying it through your bloodstream.
Excess LDL and non-HDL cholesterol can contribute to fatty build-up in artery walls over time. High triglycerides can be associated with insulin resistance, excess alcohol intake, diet, genetics and other health factors.
You may feel completely normal while these markers are elevated. That is why routine checks matter.
The British Heart Foundation explains that high cholesterol often has no symptoms, but can increase the risk of cardiovascular disease, heart attack and stroke.
Training is one part of improving cardiovascular health. So are nutrition, body composition, smoking status, alcohol intake, blood pressure and medication where appropriate.
Not every client needs the same target. Your age, medical history, family history and existing conditions affect how results should be interpreted.
4. HbA1c and glucose: how you handle fuel
Glucose is a major fuel source for the brain and working muscles.
HbA1c estimates your average blood glucose exposure over roughly the previous two to three months. It does this by measuring the amount of glucose attached to haemoglobin.
That makes it different from a single fasting glucose reading, which is only a snapshot.
Poor glucose regulation can affect energy, appetite, body composition and long-term cardiovascular health. It may also contribute to inconsistent training performance. You may feel fine during one session and struggle during another, depending on sleep, food intake, stress and activity.
The NHS notes that type 2 diabetes can develop without obvious symptoms. That matters because waiting until you feel unwell is not a reliable screening strategy.
HbA1c also needs context. Conditions that affect red blood cell lifespan, including some forms of anaemia, can influence the result. A clinician should interpret the number alongside other information.
5. Iron and ferritin: more than an anaemia check
Iron is needed to make haemoglobin and support oxygen transport. It also contributes to energy production and normal immune function.
Ferritin is a storage protein that gives an indication of iron stores. Low ferritin can occur before full iron-deficiency anaemia develops.
That may present as:
- Unusual fatigue.
- Heavy legs.
- Reduced exercise tolerance.
- Poor concentration.
- Higher perceived effort.
- Slower recovery.
Iron status deserves particular attention in people with heavy menstrual bleeding, endurance training demands, restrictive diets or a history of deficiency.
Ferritin is not perfect. It can rise during inflammation, infection or illness, so it should not be read in isolation.
Do not begin high-dose iron supplements because a result looks low on an online report. The cause matters. The NHS guidance on iron-deficiency anaemia makes this clear: the reason for the deficiency should be investigated and treatment guided appropriately.
6. Thyroid and testosterone: important, but easy to oversimplify
Thyroid hormones influence metabolic rate, temperature regulation, energy use and many systems involved in normal function.
A typical first-line thyroid assessment includes TSH, sometimes alongside free T4. An underactive thyroid may be associated with fatigue, feeling cold, weight gain, poor concentration and reduced exercise tolerance. The NHS explains how TSH and T4 are used to investigate hypothyroidism.
Testosterone supports muscle mass, strength, bone health, red blood cell production, libido and general wellbeing. Low testosterone can be associated with low energy, reduced training response and changes in body composition.
But one testosterone result does not diagnose a problem.
Levels vary with age, biological sex, time of day, sleep, energy intake, illness, medication and training stress. Total testosterone may also need to be considered alongside binding proteins and free testosterone.
More is not automatically better. Unsupervised hormone use can affect fertility, blood pressure, lipids, liver function and cardiovascular risk.
If hormone results are abnormal or symptoms are persistent, speak to a qualified healthcare professional. A coach can help you adjust training while that process happens. A coach should not diagnose or prescribe.
7. Vitamin D: bone, muscle and immune function
Vitamin D helps regulate calcium absorption and contributes to bone health, muscle function and immune function.
Low levels are more common when sun exposure is limited. That can be relevant in the UK, particularly during darker months or for people who spend most of the day indoors.
For training, the main concerns are sensible:
- Bone health.
- Muscle function.
- Injury risk where deficiency is significant.
- General health and immune resilience.
The relevant blood marker is usually 25-hydroxy vitamin D.
Testing can be useful when risk factors or symptoms suggest it. Supplementation should still be discussed with a healthcare professional. More is not better, and excessive intake can be harmful.
8. hs-CRP: a useful inflammation signal
High-sensitivity C-reactive protein, or hs-CRP, measures low levels of a protein produced in response to inflammation.
It can contribute to cardiovascular risk assessment and may reflect a broader inflammatory burden. Factors such as infection, poor sleep, higher body fat, smoking, stress and some medical conditions can affect it.
Hard training can also temporarily influence inflammatory markers. A result taken immediately after a demanding session may not represent your normal baseline.
That means hs-CRP is a trend marker, not a verdict.
A raised result should not be labelled as “overtraining” from one number. It needs context, repeat testing where appropriate and medical interpretation.
9. Kidney and liver function: recovery has to be supported by the whole system
Kidney markers commonly include creatinine, estimated glomerular filtration rate, urea and electrolytes.
The kidneys help regulate fluid balance, electrolytes and waste removal. Creatinine is produced partly through normal muscle metabolism, so muscular clients can have higher creatinine without having kidney disease. Recent training, hydration and muscle mass all matter.
Liver panels may include ALT, AST, GGT, ALP and bilirubin. The liver is involved in nutrient processing, energy storage, medication metabolism and many other functions.
AST can rise after strenuous training because it is also found in muscle tissue. That does not mean an abnormal result should be ignored. It means it should be interpreted properly, alongside other markers and recent training history.
Kidney and liver results can be particularly relevant if you take regular medication, use supplements, drink heavily, have a medical condition or are preparing for high training volumes.
Blood work should inform decisions, not create anxiety
A blood test is a snapshot.
Your result can be influenced by:
- Hydration.
- Recent training.
- Sleep.
- Illness.
- Food intake.
- Medication and supplements.
- Time of day.
- Age and sex.
- Existing medical conditions.
- The laboratory’s testing method.
Reference ranges vary between laboratories and do not always represent an ideal target for every person. A result outside the range does not automatically mean disease. A result inside the range does not guarantee that everything is perfect.
Do not self-diagnose from a report. Discuss your results with a qualified healthcare professional, especially if you have symptoms or several abnormal markers.
At AM Coaching, the useful question is not, “Can this number make the programme look more scientific?”
It is, “Does this information help us train you more appropriately?”
That may mean maintaining the plan. It may mean reducing load while a health issue is investigated. It may mean adding more recovery, improving nutrition or referring you to your GP.
Same standards. Different week.
We’re exploring how routine blood testing could become more practical for training clients at JD Gyms Southampton Bitterne. The purpose is not to sell medical services or turn coaching into a clinic. It is to support better conversations between clients, coaches and healthcare professionals.
Train hard enough. Recover enough. Check the important things when there is a reason to check them.
Learn how AM Coaching applies training science in practical 45-minute sessions, or apply and tell Adam about your goal, schedule and preferred format.
Medical disclaimer: This article is for general education and is not medical advice. Blood tests should be requested and discussed with a qualified healthcare professional. Reference ranges vary between laboratories, and results must be interpreted in context rather than used for self-diagnosis. If you have symptoms, a known medical condition or concerns about your results, speak with your GP or another appropriate healthcare professional.