High-intensity interval exercise
Children in the HIIE group were arranged in different lanes of the athletic field according to their MAS and performed 2 sets of 15 × 20s bouts of a high-intensity run (85% MAS, about 80–85% HRmax) separated by 15 × 20s active recovery bouts at low-intensity (50% MAS, about 45–50% HRmax), with 5 min rest between the 2 sets while the total duration time was 25 min. All children strictly kept the required running speed on a straight with marks track by listening to signals emitted from pre-recorded audio throughout the training session. For example, children in HIIE group may be calculated an average MAS 9.0 km/h (2.5 m/s, at 100% of MAS), they had to run 42 m in 20s (2.1 m/s, at 85% of MAS), which was followed by an active recovery to run about 26 m in 20s (1.3 m/s, at 50% of MAS) (Fig. 
Illustration of a HIIE session including specific information about intensity, distance, sets, bouts, training time and recovery time