Objectives We aimed to explore the impact of an ultra-endurance race on continuously measured glycaemia and to understand potential physiological mechanisms, as well as the consequences for performance and behavioural alertness. Methods Fifty-five athletes (78% men, 43.7 +/- 9.6 years) ran a 156-km ultra-trail race (‘Trail Scientifique de Clécy’: six 26-km laps, total elevation +6000 m). Participants wore a masked continuous glucose monitoring sensor from the day before the race until 10 days post-race. Blood was taken at rest, during refuelling stops after each lap, and after 24-h recovery. Running intensity (% heart rate reserve), performance (lap times), psychological stress and behavioural alertness were explored. Linear mixed models and logistic regressions were carried out. Results No higher risk of hypo or hyperglycaemia was observed during the exercise phases of the race (i.e., excluding stops for scientific measurements and refuelling) compared with resting values. Laps comprising a greater proportion of time spent at maximal aerobic intensity were nevertheless associated with more time >180 mg/dL (P=0.021). A major risk of hyperglycaemia appeared during the 48-h post-race period compared with pre-race (P<0.05), with 31.9% of the participants spending time >180 mg/dL during recovery vs. 5.5% during resting. Changes in circulating insulin, cortisol and free fatty acids followed profiles comparable with those usually observed during traditional aerobic exercise. However, creatine phosphokinase, and to a lesser extent lactate dehydrogenase, increased exponentially during the race (P<0.001) and remained high at 24-h post-race (P<0.001; respectively 43.6 and 1.8 times higher vs. resting). Glycaemic metrics did not influence physical performance nor behavioural alertness. Conclusion Ultra-endurance athletes were exposed to hyperglycaemia during the 48-h post-race period, possibly linked to muscle damage and inflammation. Strategies to mitigate muscle damage or subsequent inflammation before or after ultra-trail races could limit recovery hyperglycaemia and hence its related adverse health consequences.

This file contains values of continuous interstitial glucose monitoring at rest (using a professional masked continuous glucose monitoring (CGM) sensor; Freestyle Libre Pro IQ, Abbott®; a value every 15 min).

This file contains values of continuous interstitial glucose monitoring at +2h, +8h, +12h, +24h and +48h of recovery.

This file contains results of psychomotor vigilance task and KSS.Psychomotor vigilance task: on the day before the race, on the morning of the race, at the end of each lap, and at the end of the race, the runners performed a 5-min series response time test.Sleepiness: on the day before the race, on the morning of the race, at the end of each lap, and at the end of the race, a measure of the subjective level of sleepiness using the KSS was carried out.

This file contains participants characteristics, initial psychological stress level (STAI), nap time and values of continuous interstitial glucose monitoring during the race.Skeletal muscle mass was assessed on the morning of the race, using an mBCA 525 (Seca) impedance meter in the supine position.This file also provides the percentage of time spent (during each lap) in three aerobic endurance exercise intensity ranges: 1) light to moderate (up to 59% HRR), 2) vigorous (from 60 to 89% HRR) and 3) maximal (from 90 to 100% HRR).

This file contains values of continuous interstitial glucose monitoring during day or night for the first 4 days of recovery.

This file contains the total time spent competing in the race (in minutes) for all finishers.

Informations about files

This file contains values of venous blood glucose, hormones regulating glycaemia (insulin, cortisol), metabolites (free fatty acids; ß-hydroxybutyrate) and markers of muscle damage (creatine phosphokinase; lactate dehydrogenase).Blood samples were collected from the median cubital vein, in a sitting position, on the morning before the start of the race (after breakfast), at the end of each lap and at the end of the race (after visiting the refreshment canteen), and 24 h after the end of the race.

This file contains values of continuous interstitial glucose monitoring from day 1 to day 10 of recovery.