Continuous Glucose Monitoring in Endurance Athletes: Interpretation and Relevance of Measurements for Improving Performance and Health

Abstract

Blood glucose regulation has been studied for well over a century as it is intimately related to metabolic health. Research in glucose transport and uptake has also been substantial within the field of exercise physiology as glucose delivery to the working muscles affects exercise capacity and athletic achievements. However, although exceptions exist, less focus has been on blood glucose as a parameter to optimize training and competition outcomes in athletes with normal glucose control. During the last years, measuring glucose has gained popularity within the sports community and successful endurance athletes have been seen with skin-mounted sensors for continuous glucose monitoring (CGM). The technique offers real-time recording of glucose concentrations in the interstitium, which is assumed to be equivalent to concentrations in the blood. Although continuous measurements of a parameter that is intimately connected to metabolism and health can seem appealing, there is no current consensus on how to interpret measurements within this context. Well-defined approaches to use glucose monitoring to improve endurance athletes’ performance and health are lacking. In several studies, blood glucose regulation in endurance athletes has been shown to differ from that in healthy controls. Furthermore, endurance athletes regularly perform demanding training sessions and can be exposed to high or low energy and/or carbohydrate availability, which can affect blood glucose levels and regulation. In this current opinion, we aim to discuss blood glucose regulation in endurance athletes and highlight the existing research on glucose monitoring for performance and health in this population.

Continuous Monitoring of Interstitial Fluid Glucose Responses to Endurance Exercise with Different Levels of Carbohydrate Intake

“…Thus, blood glucose concentrations are maintained during exercise unless hepatic glycogen stores become markedly low [2]. Endurance athletes have a strong capacity to maintain their blood glucose concentrations during prolonged exercise compared to untrained subjects [3]. Moreover, 40% of endurance athletes present with glucose concentrations above the reference range for more than 70% of the time, except 2 h after a meal [4].…”

The Impact of Sex, Body Mass Index, Age, Exercise Type and Exercise Duration on Interstitial Glucose Levels during Exercise

“…Unfortunately, CGM accuracy overall during exercise may be less than what is observed at rest, at least in people living with type 1 diabetes [28], but it is likely that any sensor error would be consistent when generating a normative dataset that compares user characteristics, such as age, sex and/or body mass index status. The utility of CGM as a performance-enhancing tool or a monitoring tool for physically active people, including athletes without diabetes, has more recently been described [29,30], but again a normative dataset might be of some comparative value given the expanse of CGM use in the nondiabetic population, who tend to range widely in age, weight and exercise preferences.…”

Carbohydrate Ingestion Increases Interstitial Glucose and Mitigates Neuromuscular Fatigue During Single-Leg Knee Extensions

“…Current systems are deemed reasonably accurate for use during exercise for glucose concentration ranging from ~35 to 400 mg•dL −1 (~13% mean absolute relative difference from clinical measures of glucose in the bloodstream), which can be observed during exercise in those living with type 1 diabetes (21). An emerging application of CGM, however, has been its use by nondiabetic athletes to optimize CHO intake before and during exercise based on a continuous tracking of interstitial glucose (22)(23)(24)(25). The use of CGM might help ensure that sufficient CHO is being ingested to help maintain circulating glucose levels to act as a fuel for contracting muscle, and the central nervous system, amidst fatigue onset.…”