Adjusting the Yo-Yo IRT-1 equation to estimate VO2max of sub-elite football referees: a gender-comparative study

Background: To gain optimal positioning to make sure the game laws are applied in uniform way, the performance of field referee must be periodically evaluated to have constantly adequate training during a match and during the competitive season. Considering that field Yo-Yo Intermittent Recovery Test-Level 1 is frequently employed in elite team sport players to estimate maximal oxygen uptake (VO2max) in field settings, the aim of this cross-sectional, gender-comparative study was to develop a new adjusted Yo-Yo-1 equation for estimating VO2max in football referees. Methods: During off-season, 20 male (21.2±3.6 yrs) and 20 female (22.5±4.6 yrs) sub-elite football referees underwent laboratory treadmill test and Yo-Yo-1. Results: VO2max during Yo-Yo-1 and laboratory treadmill test were significantly correlated in the whole sample (r=0.871; P<0.0001), women (r=0.861; P<0.0001) and men (r=0.800; P<0.0001). Only in women VO2max during Yo-Yo-1 was lower than laboratory treadmill test (-4.3%; P=0.014). Adjusted formulae (pooled and gender-based) allowed to mitigate the underestimated values of laboratory treadmill test of VO2max found with the Bangsbo's equation (pooled sample: -14.9%, P<0.0001; women: -13.2%, P<0.0001; men: -16.4%, P<0.0001). Conclusions: Adjusted Yo-Yo-1 equations allow to accurately monitor changes in cardiopulmonary performance, and based on this, administer constantly adequate training loads, in male and female field referees.