METHODS
Participants
Eighteen male soccer players recruited from the Junior Soccer Team ‘Cagliari Calcio S.P.A.’ (age: 16 ± 0 years; body mass: 65 ± 10 kg; height: 1.74 ± 0.10 m; BMI: 21.3 ± 1.5 kg m–2) volunteered to participate in this study. The inclusion criteria were: elite national-level soccer practice, >5 years training (9.3 ± 0.8 years) and >8 hours of training per week in addition to the weekly official game. The participants were familiar with shuttle running training and had been participating at the national championships (middle season) at the time
of the investigation. The participants gave their assent, and written consent was obtained from participants’ parents/guardians after being thoroughly informed about the purpose, benefits and potential risks of the study, in conformity with the Ethics Code of the World Medical Association (Declaration of Helsinki). All experimental procedures were approved by
the institutional human ethics committee, which followed ethical standards(CONI Italian Olympic Committee, Sardinia).