19 adolescents ( 9 male , 13.70.4 years old ) completed three 1-day trials in a randomised order : ( 1 ) rest ( CON ) ; or four bouts of ( 2 ) 21 min cycling at 90 % peak power with 75 s recovery ( high-intensity interval exercise ; HIIE ) ; or ( 3 ) cycling at 90 % of the gas exchange threshold ( moderate-intensity exercise ; MIE ) , which was work-matched to HIIE .