Characterization Of Normal Biomarkers Of Muscle Damage In Collegiate Athletes

Abstract

Exertional rhabdomyolysis is a serious clinical condition in which skeletal muscle is rapidly broken down, potentially leading to life-threatening systemic complications. Clinicians often diagnose rhabdomyolysis based on elevations in circulating creatine phosphokinase (CPK) and symptomology. Normal CPK and other biomarker concentrations following intense exercise are unknown. PURPOSE: This study aimed to determine reference concentrations for selected biomarkers that suggest muscle damage in athletes and examine the time-course of muscle damage biomarker responses after strenuous exertion. METHODS: 20 collegiate NCAA I football players were enrolled in the study. Serum and urine samples were collected immediately and 24 hours post strenuous practice (0h and 24h, resp). Serum samples were analyzed for biomarkers of muscle damage including a Chem26 metabolic and chemistry panel and myoglobin. Urine samples were analyzed for creatinine and myoglobin concentrations. Participants were also given Physical Symptoms Questionnaires to obtain subjective measures of symptoms that may be related to severe muscle damage, or rhabdomyolysis. RESULTS: A total of 28 samples were collected with 9 repeats. CPK levels were elevated at 0h (958.2 ± 544.1 IU/L), but trended down 24h post practice (751.0 ± 410.5IU/L, p=0.059). LDH was acutely elevated at 0h (217.9 ± 30.6 IU/L) compared to the 24h timepoint (170.3 ± 35.5 IU/L, p<0.0001). Average serum myoglobin was higher post-practice (1.31 ± 1.57 ng/mL), but decreased 24 h post-exercise (0.36 ± 0.71 ng/mL, p<0.001). Similarly, urine creatinine concentrations were higher 0h post practice (390.1 ± 164.2 mg/mL), and decreased 24h post (214.2 ± 99.4 mg/dL, p<0.0001). Urine myoglobin was also elevated at 0h post practice (18.18 ± 36.7 ng/mL), but decreased 24h post (0.66 ± 1.43 ng/mL, p=0.001). The Physical Symptoms Questionnaires did not reveal any symptoms related to severe muscle damage. CONCLUSION: Biomarkers of muscle damage were elevated immediately post strenuous exercise, but dropped 24 hours post-practice. Serum and urine biomarkers of muscle damage collected immediately post strenuous exercise are unlikely to be specific markers of rhabdomyolysis, but rather of transient exercise-induced muscle damage in a highly trained athletic population.