Team2 pro

The protocol of the graded exercise test to assess aerobic capacity has been recently described in details (Nikolaidis et al., 2018a (link)). Briefly, it consisted of running on a calibrated treadmill with initial speed of 8 km.h⁻¹ which was increasing every minute by 1 km.h⁻¹ till exhaustion. HR was recorded continuously during the test by Team2 Pro (Polar Electro Oy, Kempele, Finland). Minute ventilation and VO₂ were recorded by a gas analyzer (Fitmate Pro, Cosmed, Rome, Italy). Plateau of VO₂ (primary criterion), blood lactate, age-predicted HR_max [calculated using Tanaka’s formula, i.e., 208-0.7 × age (Tanaka et al., 2001 (link))] and rate of perceived exertion (RPE) Borg category-ratio scale (Borg, 1998 ) (secondary criteria) were used as criteria of VO₂max. Due to the difficulty identifying a plateau of VO₂, VO₂ was considered maximal once the secondary criteria were fulfilled. Blood samples were taken 5 min after termination of test [i.e., within the recommended range of 1–8 min (Howley et al., 1995 (link))], and lactate concentration was analyzed (Accutrend, Roche, Germany).

The 90-min shuttle run test was conducted according to Thompson et al. in an artificial surface soccer pitch [20 (link)]. Volunteers were required to run between two lines, 20 m apart, at various speeds dictated by an audio signal based on the velocities corresponding to their individual 55 and 95% of VO_2max. The protocol consisted of 5 blocks of continuous running separated by 3 min of passive recovery for a total duration of 90 min. Heart rate was recorded via telemetry at 5-s intervals (Polar Team2 Pro, Polar, Finland) and averaged for each set (Fig. 1).