Strength training elevates creatine kinase, AST, ALT, and creatinine. A GP sees liver damage, kidney impairment, and muscle breakdown. An athlete sees a normal training response. The problem isn't your training. It's that your results are being read by someone who doesn't understand them. A comprehensive blood test with context-aware reporting, like the TrueVitals Ultimate panel, distinguishes exercise-induced elevations from genuine pathology across 114 biomarkers.
If you train hard and get a standard GP blood test, there is a reasonable chance your doctor will flag one or more of these as concerning. Understanding why they're elevated — and when to actually worry — is the most important thing this page can tell you.
Normal sedentary range: 30 to 200 U/L. After a heavy leg session: 500 to 5,000 U/L. After intense eccentric work (heavy negatives, walking lunges, downhill running): 2,000 to 10,000+ U/L. CK has a 500,000:1 concentration gradient between muscle cells and blood, making it extremely sensitive to training. Elevated CK after training is expected and resolves within 5 to 7 days. The concern is rhabdomyolysis — CK above 10,000 U/L with dark urine, severe muscle pain, and confusion. That is a medical emergency. Everything below that threshold in the context of training is a normal adaptive response.
The fix: establish your personal rested baseline by testing after 72+ hours of rest. Track the pattern over time. Chronically elevated CK during easy weeks suggests inadequate recovery.
This is the most common misinterpretation. AST (aspartate aminotransferase) and ALT (alanine aminotransferase) are called "liver enzymes" but both are abundant in skeletal muscle. Muscle tissue actually contains more AST than the liver due to its larger total mass. After intense training, muscle cell damage releases AST and ALT into the bloodstream, mimicking liver damage on a standard panel. A GP who doesn't ask about training history will see elevated AST and ALT and investigate for hepatitis, fatty liver, or alcohol damage.
The fix: check GGT (gamma-glutamyl transferase) and bilirubin. These are genuinely liver-specific. If GGT and bilirubin are normal while AST and ALT are elevated, the elevation is almost certainly exercise-induced. If GGT is also elevated, investigate the liver. This distinction is why testing the full liver panel matters, not just ALT and AST.
Creatinine is a breakdown product of creatine phosphate in muscle. People with more muscle mass produce more creatinine. People supplementing creatine (3 to 5g daily, the most evidence-based sports supplement in existence) produce significantly more. The eGFR (estimated glomerular filtration rate) is calculated from creatinine, so elevated creatinine produces an artificially low eGFR. A GP sees a low eGFR and flags kidney impairment. The kidneys are fine. The test is being confounded by the supplement.
The fix: cystatin C is an alternative kidney function marker unaffected by muscle mass or creatine supplementation. If cystatin C-based eGFR is normal while creatinine-based eGFR is low, the kidneys are fine. The TrueVitals Ultimate panel includes cystatin C for exactly this reason.
Gym-goers consuming 1.6 to 2.5g protein per kilogram of bodyweight daily produce more urea as a byproduct of protein metabolism. Elevated urea alongside elevated creatinine on a standard panel screams "kidney problem" to a GP. In a muscular person eating high protein, it's dietary, not pathological. Again, cystatin C separates the two.
Testosterone can be suppressed for up to 72 hours after intense training. A blood test taken the morning after a heavy session may show testosterone significantly lower than your true resting level. This is not hypogonadism. It's acute suppression. Test after 48 to 72 hours of rest, before 10am (when testosterone peaks), for an accurate baseline. Testosterone blood test guide.
The markers above look alarming but are usually fine. These markers below are the ones that genuinely affect your training, recovery, and long-term health.
Total testosterone tells half the story. SHBG determines how much is biologically available (free testosterone). High SHBG with normal total T means low free T and reduced anabolic signalling. Track both over training cycles to see whether your programme supports or suppresses hormonal output.
The balance between catabolic (cortisol) and anabolic (testosterone) processes. When cortisol rises while testosterone falls, you're accumulating stress faster than you're recovering. This pattern over multiple tests is the most reliable blood-based indicator of overreaching or overtraining.
Thyroid dysfunction mimics overtraining exactly: fatigue, strength loss, poor recovery, weight gain despite training. Free T3 is the active hormone. TSH alone misses subclinical issues. Testing the full panel separates genuine overtraining from thyroid pathology. Thyroid guide.
Training hard does not guarantee cardiovascular health. High-calorie bulking diets, high saturated fat intake, and certain supplement stacks can elevate ApoB and LDL regardless of fitness level. ApoB is a better predictor of cardiovascular risk than standard LDL cholesterol. Cholesterol guide.
Vitamin D affects muscle function, bone density, testosterone production, immune function, and recovery. Deficiency is common in UK gym-goers who train indoors year-round. Target 75 to 125 nmol/L. NHS deficiency threshold is 25 nmol/L, which is far too low for active people.
Resistance training improves insulin sensitivity, but high-calorie surplus phases can impair it. Fasting insulin and HOMA-IR reveal metabolic efficiency independent of training. Important for anyone cycling through bulk and cut phases to confirm the bulk didn't create a metabolic problem. Metabolic guide.
The TrueVitals Ultimate panel includes testosterone, SHBG, free T, cortisol, full thyroid, ApoB, Lp(a), fasting insulin, HOMA-IR, cystatin C, full liver with GGT, vitamin D, B12, ferritin, and 100+ additional markers. 114 biomarkers. Results in 48 hours. £349.
If you supplement, you need to know how each one interacts with your blood work. Otherwise you'll chase phantom problems or miss real ones.
Raises creatinine (kidney marker) and lowers eGFR without affecting kidney function. Use cystatin C for true kidney assessment. Tell your reviewer you supplement creatine.
Interferes with immunoassay-based tests. Can produce falsely normal or falsely abnormal results for thyroid, hormones, and cardiac markers. Stop biotin 48 to 72 hours before testing.
Supplementation shows directly in your 25(OH)D level. If you supplement 2,000 to 4,000 IU daily, your level should be 75 to 125 nmol/L. If it's still below 50 nmol/L despite supplementation, you may have an absorption issue or need a higher dose.
If supplementing iron, test to confirm you're reaching target ferritin (50 to 70+ ng/mL for athletes). Also test to avoid over-supplementation — ferritin above 200 ng/mL in men or 150 ng/mL in women warrants investigation.
High protein intake (1.6 to 2.5g/kg/day) elevates urea and creatinine. This is metabolic, not pathological. Combined with creatine, these markers can look alarming. Cystatin C resolves the ambiguity.
Rest 48 to 72 hours before testing. CK, AST, ALT, cortisol, and testosterone are all significantly affected by acute training. Testing the morning after a heavy session gives you a snapshot of training stress, not your baseline health. Test after 2 full rest days or during a deload week.
Test before 10am. Testosterone peaks in the early morning. Cortisol follows the circadian rhythm (highest at waking, declining throughout the day). Morning testing gives the most consistent, comparable results for hormonal markers.
Fast 10 to 12 hours. For panels with fasting glucose, fasting insulin, and lipids. Stop eating at 10pm the night before. Drink water normally. Coffee counts as breaking the fast.
Stop biotin 48 to 72 hours before. If you take a multivitamin or B-complex containing biotin, check the label and stop it 2 to 3 days before your test.
Test 2 to 3 times per year. Pre-training block, mid-block, and post-block gives you the most useful data. At minimum, test annually. Serial testing reveals how your programme, nutrition, and recovery are affecting your body over time. One snapshot tells you where you are. Two snapshots tell you where you're heading.
A CK of 800 U/L after a deload week means something different from 800 U/L 48 hours after a heavy squat session. The TrueVitals report applies context-aware interpretation. It separates exercise-induced elevations from genuine pathology using marker-specific logic: elevated AST/ALT with normal GGT and bilirubin is flagged as likely exercise-related, not liver damage. Elevated creatinine with normal cystatin C is flagged as creatine or muscle mass artefact, not kidney impairment. The report provides specific recommendations for training, nutrition, supplementation, and recovery based on your actual data.
114 biomarkers including testosterone, cortisol, full liver with GGT, cystatin C, ApoB, fasting insulin, and every marker that separates training adaptation from damage. Results in 48 hours.
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