After a tough leg workout, a blood marker of muscle damage (CK) spikes by more than 1.5 times and stays high for two days, showing the muscles are still healing.
Scientific Claim
Serum creatine kinase activity increases by approximately 164% at 24 hours and 105% at 48 hours after heavy resistance exercise in strength-trained men, indicating ongoing muscle cell membrane disruption.
Original Statement
“Serum CK activity increased from 90 ± 34 to 238 ± 111 IU·L−1 (p < 0.05) and 185 ± 91 IU·L−1 (p < 0.05) at 24 and 48 hours after the exercise, respectively.”
Evidence Quality Assessment
Claim Status
appropriately stated
Study Design Support
Design supports claim
Appropriate Language Strength
association
Can only show association/correlation
Assessment Explanation
The claim accurately reports the magnitude and timing of CK changes observed in the study without implying causation. The design supports quantitative associations.
Evidence from Studies
Supporting (1)
The study found that after intense weight training, a marker of muscle damage (creatine kinase) went up in the blood for at least two days — which means the muscles were still getting repaired, just like the claim says.