Assessment of Blood Glucose Responses in a Female National-Level Marathon Runner Using Continuous Glucose Monitoring during a Real-World Marathon Race

Background: The effects of the use of continuous glucose monitoring (CGM) in elite endurance athletes are unclear. This case study reported the blood glucose (BG) levels of a female national-level marathon runner during a real-world marathon race. Methods: Heart rate and BG levels were monitored throughout the race. Results: The runner completed the race in 2:46 h:min, which was an improvement from her previous personal record by just under one min. Her BG levels were stable from approximately 5–40 km of the race at a mean concentration of 7.13 mmol/L, with a standard deviation of 0.20 mmol/L and a coefficient of variation of 2.8%. Increases in BG levels and heart rate were observed 6 min after the race and during the 40–42.195 km section, respectively. Conclusions: The runner broke her own record and exhibited stable BG levels throughout the race, with the highest BG value detected immediately after the race. Considering that quantity, content, and timing of pre-race meals and supplementation during the race can affect BG levels, future studies should assess additional detailed parameters in more detail and monitor multiple races with the same elite endurance athletes to acquire more definitive evidence on CGM usefulness among elite endurance athletes.