Authors
Emma E. Plank, Department of Exercise Science, Grove City College, Grove City, Pennsylvania, USA
Timothy D. Noakes, Department of Medical and Wellness Science, Cape Peninsula University of Technology, Cape Town, South Africa
Jeffrey D. Buxton, Department of Exercise Science, Grove City College, Grove City, Pennsylvania, USA
Philip J. Prins, Department of Exercise Science, Grove City College, Grove City, Pennsylvania, USA
International Journal of Exercise Science 19(6): 1-11, 2026.
Abstract
This is a retrospective single-case analysis that describes pacing and physiological responses in a highly trained keto-adapted triathlete during an Ironman triathlon using descriptive statistics only. Exercise-induced hypoglycemia (EIH) may be a primary contributor to fatigue and impaired performance during prolonged exercise. As there are only 4-5 grams of glucose circulating in the bloodstream, minimal carbohydrate supplementation may be able to maintain euglycemia during endurance and ultra-endurance competition. The purpose of this case study was to retrospectively examine the use of minimal carbohydrate supplementation (≤10 grams/hour) in a highly trained, keto-adapted triathlete on pace maintenance, average heart rate (AHR), and maximal heart rate (HRmax). Percent change was calculated for the first, middle, and last 30 minutes of each of the three disciplines to assess pacing and physiological measurements. Percent deviation from the overall discipline average was calculated for each measure of interest to evaluate performance stability. Despite minimal deviation in AHR and HRmax during the final 30 minutes of the run (0.71% and 0.14%, respectively), there was an observable decline in pace (13.63% deviation and 23.40% slower pace from first to last 30 minutes) when the athlete stopped ingesting CHO during the last hour, coinciding with the onset of mild symptoms consistent with EIH upon the completion of the triathlon. These findings are observational and suggest the continued ingestion of minimal CHO may have helped maintain euglycemia and potentially preserved pace during the final hour of the race, although fatigue may also have been due to other factors.