Study design

A longitudinal study was conducted in July 2015 that evaluated 28 race walkers, including 24 men and 4 women, who participated in the “Ecological Walk of Goiás—2015” [7, 8]. The participants walked 310 km in 5 days (average 62 km/day), consisting of alternating periods of fast walking and running, at an average speed of 7.6 km/h.

During the walk, which was characterized by wide variability in temperature and air humidity (16 to 33 °C and 21 to 76%, respectively), water and electrolytes were offered every hour to keep participants hydrated, and snacks, as advised by the Nutrition team, were consumed at an average frequency of every 2 h. In the middle of the day, a break of approximately 2 h was given for lunch, rest, and dressing, according to each walker’s needs. An ambulance with a healthcare team followed the walkers throughout the entire walk (5 days).

Blood samples were collected during the initial interview, in the morning while fasting, and at the end of each day of the walk, at approximately 7 pm, 5 to 60 min after finishing the activity, with the exception of the last day, when no blood was collected for logistical reasons.

Blood was collected through peripheral venous access by a team trained in that technique. For each collection, approximately 5 mL of blood was extracted. One drop of the blood was applied on a blood glucose test strip of the Accu-chek active glucometer (Roche) for determination of capillary blood glucose, and the remaining sample was centrifuged at the collection site at 3000 rpm for 10 min to obtain serum/plasma. Samples were immediately stored at − 20 °C for further analysis.