Journal of Exercise Physiologyonline Official Journal of The American Society of Exercise Physiologists (ASEP)

ENERGY BALANCE DURING 24 HOURS OF TREADMILL RUNNING. Linderman, Jon K., Laubach, Lloyd L. JEPonline. 2004;7(1):37-44. The purpose of the present investigation was to assess energy expenditure (EE) and energy intake (EI) during a continuous 24-hour treadmill run. EE was determined from heart rate (HR) telemetry, utilizing a linear relationship between VO2 and HR obtained during a maximal exercise test. EE was also estimated using a common metabolic calculation. The 51 year-old male ultra-marathon runner completed 160 km in 21 hours 59 minutes, and amassed 172 km in 24 hours. Subject’s HR averaged 119 ± 8 beats/min and average hourly HR changed as a function of hourly velocity (r = 0.80). Total EE estimated from HR telemetry and a metabolic equation was 12,820 and 12,425 Kcals, respectively. Total EI, 4590 kcal, came almost exclusively from carbohydrate. Blood glucose ranged between 8.2 and 4.1 mmol/L, averaging 5.6 ± 1.1 mmol/L. Estimated lipid oxidation accounted for 5,000 Kcals, and oxidation of carbohydrate accounted for another 1,900 Kcals. Remaining energy was likely supplied through direct oxidation of lactate as well as gluconeogenesis. Our results indicate that the subject experienced a substantial caloric deficit similar to that seen in other ultra-marathon runners, but did not exhibit hypoglycemia. We conclude that EI was sufficient to supplement endogenous substrate utilization and maintain euglycemia for the duration of the 24-hour run