Serum creatine kinase elevations in ultramarathon runners at high altitude American researchers have studied at a 100-mile run in Colorado to 2800-3840 m what happens to the CK (creatine kinase, marker for muscle damage).From 669 starters 352 runners came to the finish within the time limit.
In 36 runners, the CK could be determined before and after the barrel.The CK rose to values by 15'000 u / l. All other details can be found under https://pubmed.ncbi.nlm.nih.gov/28075653/