Introduction: The purpose of this pilot study was to assess for biomarkers indicative of passing intense physical training and establishing normative values within the tactical athlete population. Unfortunately, none of the biomarkers assessed were indicative of passing training, however, glucose, blood urea nitrogen, and creatine kinase (CK) levels stood out as abnormal. CK levels are commonly used in conjunction with muscle pain and/or myoglobinurea to diagnose exertional rhabdomyolysis (ER) in athletes and the military population. However, research shows that high CK levels may not correlate with acute kidney failure in ER.
Materials and methods: After IRB approval and informed consent, blood samples were obtained from 21 volunteers during two phases of the combat control training pipeline: the first phase (12 participants) was 2 hours of daily physical training followed by 8 hours of academics, and the second phase (nine volunteers) a grueling, 72 hour, intense training cycle (stress inoculation training, SIT) with a historic pass rate of only 50%. Biomarkers were also tracked 48 hours after cessation of SIT.
Results: None of the biomarkers assessed showed a correlation with passing SIT, but high CK levels were well above the diagnostic threshold for ER-as high as 28,000 u/L. At a single point in time, a significant correlation did not exist between CK and others markers associated with rhabdomyolysis. Across time, partial correlations controlling for subject did exist between CK and other markers.
Conclusions: In our low-powered case control study (pilot study), a nonpathologic elevation of CK is prevalent in high-intensity military training, but not shown to correlate with values associated with acute kidney injury. We assume that real-time collection of these markers could be used once sensors are capable of real-time collection and have the potential for diagnostic affordance. When measured in a between subjects design, our study showed a lack of significance when correlating markers of acute renal injury and elevation of CK. However, when utilized for tracking purposes (within subjects design), the results do show a positive correlation between CK and renal failure biomarkers-specifically only at high physiological stress points.
Published by Oxford University Press on behalf of the Association of Military Surgeons of the United States 2020. This work is written by (a) US Government employee(s) and is in the public domain in the US.