Day-to-Day Glycemic Variability Using Continuous Glucose Monitors in Endurance Athletes

Original Article Day-to-Day Glycemic Variability Using Continuous Glucose Monitors in Endurance Athletes

Abstract

Objectives: The application of continuous glucose monitors to measure interstitial glucose in athletic populations is limited by the lack of accepted athlete-specific reference values. The aim of this study was to develop athlete-specific reference ranges for glycemic variability under standardized diet and exercise conditions.

Methods: A total of twelve elite racewalkers "n equals seven" men, "twenty-two point four plus or minus three point five," "V O two max" "point six plus or minus seven point three" milliliters per kilogram per minute completed two four-day trials separated by four days. Athletes were provided a high-energy, high-carbohydrate diet "two hundred twenty-five plus one point six kilograms per day," "eight point four zero point three" grams per kilogram per day, carbohydrate and completed standardized daily exercise. The timing of food consumed and exercise undertaken were matched each day across the four-day trials. Interstitial glucose data were collected via Freestyle Libre two continuous glucose monitors. Glycemic variability was calculated as the mean amplitude of glycemic excursions, mean of daily differences, and standard deviation.

Results: Twenty-four hour mean of daily differences, mean amplitude of glycemic excursions, and standard deviation for interstitial glucose were "twelve point six plus or minus one point eight milligrams per deciliter" (zero point seven plus or minus zero point one millimoles per liter), "thirty-six point zero plus or minus five point four milligrams per deciliter" "two point zero plus or minus zero point three millimoles per liter," and "sixteen point two one point eight" milligrams per deciliter "zero point nine plus or minus zero point one millimoles per liter," respectively. Twenty-four hour mean glucose "one hundred two point six plus or minus five point four milligrams per deciliter" "five point seven plus or minus zero point three millimoles per liter" was higher than overnight "ninety-one point eight plus or minus five point four milligrams per deciliter" "five point zero plus or minus zero point three millimoles per liter"; "P less than point zero zero zero one" and was lower in women than men "ninety-nine point zero three point six" milligrams per deciliter "five point five plus or minus zero point two millimoles per liter" versus one hundred four point four plus or minus three point six milligrams per deciliter "five point eight plus or minus zero point two millimoles per liter" "P equals point zero five nine,"

"d equals one point four." Conclusions: This study provides reference indices under standardized diet and exercise conditions for glycemic variability derived from continuous glucose monitors in endurance athletes which are similar to previously reported for healthy individuals, despite strenuous daily training and a high daily energy and carbohydrate diet.

Introduction

cose snapshots every one to fifteen minutes alongside twenty-four hour periods of continuous glucose data.

Continuous glucose monitors are devices that capture daily glucose dynamics, providing the user with (near) real-time measures of interstitial glucose concentration. To collect continuous glucose metrics, continuous glucose monitors are implanted into the subcutaneous tissue of a site approved for use by the manufacturer, typically the back of the upper arm, the lower back or the abdomen. The implanted sensor then uses a glucose-oxidase reaction to generate a current, analogous to the glucose concentration within the interstitial fluid, which is subsequently used to estimate blood glucose concentration. Once the device is implanted, information is transmitted via wireless technology to either a data receiver or mobile smartphone which enables the user to view glu-

Historically, these devices have been used by individuals living with diabetes to facilitate prompt management of undesirable glucose fluctuations. Here, continuous glucose monitor capture of time series data reflecting blood glucose responses to recent food and fluid intake and physical activity allows the adjustment of dietary intake and/or insulin dosing in (near) real-time. Indeed, it has been shown that the glucose estimates provided by continuous glucose monitors are comparable to blood glucose data collected via traditional methods, such as venous blood sampling, typically used in hospital settings or laboratories.

Following the success of these devices in the management of diabetes mellitus, continuous glucose monitors have been considered as a tool to inform daily training and fueling practices in healthy, active individuals and athletes. Recently, athlete-specific devices such as the Abbott Libre Sense Glucose Sport Biosensor and software platforms (i.e., Supersapiens, Ultrahuman) have been designed with the aim of providing active individuals and athletes with access to real-time glucose metrics including twenty-four hour glucose averages, daily glucose patterns, and hypoglycemic episodes. Although previous studies have established reference ranges for glycemic variability in individuals with diabetes mellitus and healthy non-athletic populations, there are currently no accepted reference values for athletes under standardized diet and exercise conditions. To support the interpretation of continuous glucose monitor-derived glucose values in future diet and exercise interventions, accepted athlete-specific reference ranges need to be established. Hence, the aim of this study was to develop athlete-specific continuous glucose monitor-derived glycemic variability markers under standardized exercise and dietary protocols among endurance athletes.