# Beyond Euglycemia: Case Studies Using Continuous Glucose Monitoring in Elite Athletes Without Diabetes During Record Athletic Events

## TL;DR

Elite athletes without diabetes experience extreme glucose fluctuations during intense events, showing that blood sugar levels should be interpreted based on the sport and context, not standard medical ranges.

## Contribution

This study introduces performance-specific glucose monitoring benchmarks for elite athletes, challenging the use of clinical glycemic thresholds in athletic contexts.

## Key findings

- Elite athletes without diabetes show glucose levels far beyond normal ranges during extreme sports events.
- Different sports like ultra-endurance cycling and breath-hold diving produce distinct and reproducible glucose patterns.
- High glucose levels during performance may be adaptive, not harmful, and should be interpreted with sport-specific context.

## Abstract

What are the main findings?
CGM revealed markedly different glucose responses in elite athletes without diabetes depending on exercise modality, intensity, and fueling strategy, with both hypoglycemic and hyperglycemic excursions occurring well outside conventional euglycemic ranges.Extreme and discipline-specific physiological stressors, including intermittent ultra-endurance cycling, uninterrupted prolonged climbing, and hypoxic breath-hold diving, produced distinct and reproducible CGM patterns despite preserving metabolic health.

CGM revealed markedly different glucose responses in elite athletes without diabetes depending on exercise modality, intensity, and fueling strategy, with both hypoglycemic and hyperglycemic excursions occurring well outside conventional euglycemic ranges.

Extreme and discipline-specific physiological stressors, including intermittent ultra-endurance cycling, uninterrupted prolonged climbing, and hypoxic breath-hold diving, produced distinct and reproducible CGM patterns despite preserving metabolic health.

What are the implications of the main findings?
CGM metrics and clinical glycemic thresholds require context-specific interpretation in elite sport, as transient deviations from euglycemia may reflect adaptive physiological responses rather than metabolic dysfunction.These findings support the development of sport- and task-specific CGM benchmarks and highlight the need to integrate CGM data with exercise context, fueling practices, and performance demands when applied in high-performance settings.

CGM metrics and clinical glycemic thresholds require context-specific interpretation in elite sport, as transient deviations from euglycemia may reflect adaptive physiological responses rather than metabolic dysfunction.

These findings support the development of sport- and task-specific CGM benchmarks and highlight the need to integrate CGM data with exercise context, fueling practices, and performance demands when applied in high-performance settings.

Glucose data regarding extreme elite performances in athletes without diabetes remains limited. The purpose is to characterize continuous glucose monitoring (CGM) responses in elite athletes across distinct high-performance contexts. This descriptive case series includes three separate elite athletes who used a CGM during their respective sporting events. The first is an ultra-endurance relay cycling world-record performance (Race Across the West, RAW), the second is a continuous high-intensity Everesting Challenge cycling record attempt, and the third is a maximal constant-weight no-fins breath-hold depth dive performed in international competition. Glycemic outcomes, as measured by CGM, included mean, maximum, and minimum glucose, glucose standard deviation (SD), and the percentage of time in tight glucose range (TITR: 70–140 mg/dL; 3.9–7.8 mmol/L), time below range (TBR: <70 mg/dL; <3.9 mmol/L), and time above range (TAR140: >140 mg/dL; >7.8 mmol/L). Other performance data, including peak power, heart rate, and lactate, are also provided where available. During the RAW challenge lasting 44 h and 20 min, mean glucose was 91 ± 23.2 mg/dL (mean ± SD) with 9.15% TBR and 35.58% TITR during cycling and 115 ± 24.7 mg/dL with 9.11% TBR and 43.16% TITR during resting periods. In contrast, the Everesting Challenge cycling record attempt demonstrated a persistently elevated glucose profile (160 ± 5.7 mg/dL), minimal variability (CV 3.5%), and 100% TAR140. Following the maximal breath-hold depth dive, interstitial glucose was 100% TAR140 during recovery (187 ± 18.5 mg/dL), alongside marked elevations in blood lactate concentrations (peak 13.4 mmol/L). The series of case studies demonstrate that substantial deviations from traditional euglycemic ranges are common during elite performance in athletes without diabetes. Interpretation of CGM data in athletic settings should therefore be performance- and context-specific rather than based on clinical glycemic thresholds.