Before your blood test
Should you exercise before a blood test?
Short answer
Skip strenuous exercise for 24–48 hours before a draw. Hard workouts raise creatine kinase, AST and ALT (from muscle, not liver), creatinine, white blood cells and CRP for one to several days, and can lower or raise glucose. Normal daily activity is fine; a marathon or heavy lifting session the day before is not.
Medically reviewed by Youmna DiStefano, MD · Last reviewed September 2026
Which results does it affect?
| Marker | Direction | How long | What to do |
|---|---|---|---|
| Creatine kinase (CK) | raises | Peaks 1–3 days after hard exercise; can stay up a week | No strenuous exercise for 48–72 hours before a CK [source] |
| AST, ALT | can raise | Days after intense exercise (muscle source) | Rest 48 hours before a liver panel [source] |
| Creatinine | can raise | Hours to a day | Rest and hydrate before a kidney panel [source] |
| White blood cells | raises | Hours | Rest the morning of the draw [source] |
| CRP / hs-CRP | can raise | 1–3 days after strenuous exercise | Rest 48 hours before an inflammation marker [source] |
| Testosterone | can raise | Hours (transient) | Draw in the morning before training [source] |
Why muscle shows up in a 'liver' test
AST and ALT live in muscle as well as liver cells. Heavy training releases them along with creatine kinase, so a liver panel drawn after a hard weekend can look like liver injury when the source is muscle. A normal GGT alongside raised AST/ALT is a clue the muscle is responsible; so is a high CK.
Endurance events and unaccustomed heavy lifting cause the largest rises. Gentle activity — walking, light cycling, stretching — doesn't materially change results.
Common questions
Can I go to the gym the morning of my blood test?
Better not. Even a moderate session that morning raises white cells and can shift glucose and hormones. Draw first, train after.
My CK came back high — is that a problem?
If you trained hard in the days before, probably not; repeat after 5–7 days of rest. A persistently high CK without exercise, or with dark urine or weakness, needs a clinician.
Educational content, not a diagnosis. Lab results are one input; a clinician interprets them with your history and exam.