A study of marathon performance in elite amateur runners based on continuous glucose monitoring technology: an observational study

This observational study aimed to characterize glycemic dynamics and their association with exercise performance in elite amateur runners during a marathon race using continuous glucose monitoring (CGM). CGM was used to continuously monitor interstitial glucose concentration and exercise data of 26 elite amateur runners (24 males, 2 females) participating in the 2023 Wuxi Marathon. Generalized linear mixed models and linear mixed models were employed to examine differences across 10‑kilometer race segments, with runner as a random intercept. Correlation analyses assessed associations between glycemic variables and running speed. The mean interstitial glucose concentration during the race was significantly higher than the baseline value. Generalized linear mixed models revealed significant differences in interstitial glucose concentration across 10 kilometer segments, with decline in the 31–40 km and 41–42 km segments compared to the first 10 km. Speed analysis showed significant variations across segments, with a significant decrease during the 21–30 km, 31–40 km, and 41–42 km segments compared to the first 10 km. Correlation analysis between speed and interstitial glucose concentration indicated no significant linear relationship, either for the entire race or within individual 10‑kilometer segments. Pre‑race carbohydrate intake was not significantly associated with runners’ speed or interstitial glucose concentration during the first 10 km. A higher mean carbohydrate (CHO) intake rate during the race was associated with longer race completion time, whereas no significant correlation was found with the mean interstitial glucose concentration. The study highlights that marathon runners experience a significant increase in interstitial glucose concentration during the race, with declines in the later stages. Speed decreases significantly in the latter half of the race, particularly between 31 and 40 km. However, no significant linear correlation was found between interstitial glucose concentration and speed, and pre-race carbohydrate intake was not significantly associated with performance or glucose dynamics. These findings suggest that marathon fatigue is multifactorial, with interstitial glucose being only one of several contributing physiological factors.