Participants
After receiving a full explanation of the test requirements and risks, 12 healthy county-standard and semi-professional male football players provided written informed consent and participated. All participants were free of cardiopulmonary disease and completed a medical screening questionnaire before testing began. The age, body mass, and stature (mean ± s) of the participants were as follows: 24.6 ± 1.3 years, 75.2 ± 5.9 kg, and 179.0 ± 6.2 cm, respectively. The study was approved by the Biosciences Research Committee at the University of Portsmouth.