Total Energy Expenditure, Substrate Use and Hydration during the Ironman World Championship: A Case Study

Abstract

PURPOSE: The purpose of this study was to compare total energy expenditure (TEE) via the doubly labeled water (DLW) method to developed regression equations, determine muscle glycogen use, and hydration changes during the Ironman World Championship triathlon. METHODS: The present case study included a male athlete (39y, 182.9cm, 77.9kg). Urine samples were collected daily (AM and PM) to evaluate isotopic elimination (2H2O and H218O) for calculations of TEE and water turnover. Additional samples were also collected from researchers from the same region as the subject but not participating in the study to adjust for isotopic background shifts. Prior to race day, regression equations were developed using the relationship between expired gas and workload during steady state bike and run segments on the actual race course. Muscle biopsies were collected from the vastus lateralis approximately 2hr pre and immediately post race. Blood was analyzed and nude body weight was collected immediately prior to and following the race. RESULTS: Total energy expenditure using the DLW method for the race was 38.9 MJ (9,290 kcals) compared to the predicted 36.0 MJ (9,087 kcals) from regression analyses. Muscle glycogen concentration was decreased 68.5% (125.2 and 48.0 mmol/kg wet wt. for pre and post race, respectively). Blood Na+ remained constant at 139 mmol/L, hemoglobin and hematocrit concentration increased (Hb=15.6 g/dl to 17.3 g/dl and hematocrit=46% to 51% for pre and post race, respectively). The estimated decrease in plasma volume over the race was 18%. Body mass demonstrated a 7.5% decrease (78.6 and 72.7 kg for pre and post race, respectively). Water turnover calculated from isotopic elimination was 16.6 L. DISCUSSION: Although the DLW method for determining TEE represents the gold standard for free-living humans, accurate estimation of TEE from individual, mode specific regression analyses is possible. These results demonstrate a large flux in muscle glycogen, and total body water in response to the extreme TEE of this multi-modal ultra-endurance event. Supported by Air Force Research Laboratories, FA8650-06-1-679