Muscle Energy and Salivary Cytokine Response During a 100 Mile Trail Run: A Case Study

Abstract

PURPOSE: The purpose of this study was to determine the impact of competing in a 100-mile ultramarathon on muscle fuel stores and cytokine production. METHODS: One experienced male runner (40 yrs, 76.3 kg, 177.8 cm) completed the 100.5-mile distance in 32.9 hrs. Measurements were collected pre-race, at each support crew accessible aid station (28.5, 41, 52, 66, and 80 miles), and post-race. Measures included saliva cytokine markers (IL-6 and TNF-α), muscle energy status, and body mass. Saliva was collected using a passive drool technique and samples were stored on dry ice until they could be sent out for analysis. Muscle energy status (MES) was determined by scanning the right rectus femoris with a portable ultrasound transducer. Scanned muscle images were uploaded to a cloud-based application where they were analyzed for MES, which is an arbitrary number assigned to the muscle based on predicted glycogen concentration. Caloric expenditure was predicted based off average pace and terrain. Caloric intake was monitored by a combination of self-reporting, product wrapper collection, and unconsumed fluid measurement. RESULTS: Caloric expenditure was estimated at 13,184 kcal (401 kcal/hr), while caloric intake was recorded at 5888.3 kcal (180 kcal/hr). Body mass declined 2.4% from pre to post-race, although it fluctuated throughout the race (76.3, 74.7, 74.1, 75.1, 75.9, 75.4, 74.5 kg; respectively). MES was reduced 57% from pre to post-race, but also fluctuated throughout the race (88.0, 34.4, 71.9, 25.1, 69.1, 70.9, 38.2). IL-6 levels correlated with MES values (R2= 0.6987). TNF-α values followed a similar pattern to IL-6; however, no correlation was found between TNF-α and MES. CONCLUSION: These data provide some interesting insights into potential MES plasticity and cytokine regulation during prolonged exercise. More specifically, fluctuating MES values observed during the current activity suggest that glycogenolysis and glycogenesis may occur throughout an ultra-event depending on terrain and intensity, even with a discrepancy between caloric intake and expenditure. Additionally, salivary IL-6 activity may be related to MES, suggesting that periods of low glycogen may increase physiological stress.