During a soccer game the cardio-circulatory system is severely taxed 1, and soccer referees need to have high levels of physical fitness. To referee a soccer game, they must be alert and near the scene of action, and their level of fitness must be such that fatigue will not impair their decision-making. Referees are often subjected to proportionally increasing physical demands as years go by. Indeed, their peak performance is usually between 30 and 45 years of age, when cardiovascular athletic performance starts to decline. Several studies have investigated the athletic performance of referees 234 The aim of our study is to evaluate the morphological and functional cardiac profiles of professional soccer referees.

Long-term athletic training is associated with morphological cardiac changes, including increased left ventricular cavity dimension, wall thickness, and calculated mass, which are commonly described as "athlete's heart".

These changes seem to be adaptations to the hemodynamic load produced by long-term, frequent, intensive exercise programs. Our investigation shows that referees' hearts present an increase in left ventricular mass and normal systolic and diastolic function, similar to that in soccer players. Thus a referee's heart can also be considered a physiological athlete's heart 89.

These morphological and functional modifications may be due to the fact that during the match and weekday training the work load is sufficiently intense to cause an increase in left ventricular mass, and morphological and functional modifications in the heart over the long term.

During a match in fact, a referee covers a distance of between 7000 and 10000 meters at an average heart rate of 150 to 160 bpm and an average oxygen uptake of approximately 80% of the maximum aerobic power. 1011

Elite soccer referees usually reach the peak of their careers at a considerably greater average age than competitive soccer players. Thus, referees perform best physically at a time when their cardiovascular performances start to decline.

So even if referees are older than soccer players, our echocardiographyc study shows how the referee's heart presents morphological adaptations like soccer, including similar parameters and an increase in left ventricular mass (both due to the training work load). For this reason the referee's cardiovascular adaptations allow the same soccer's players performance

The differences between first-division referees and elite soccer players may result from the different workloads undergone during both match and training. In fact, during an official match, soccer players cover a distance of between 8 and 12 km, with a speed of between 10 to19 Km/h, but their training load during the week is usually five days of training sessions plus the official match. The soccer players usually underwent training with a predominant increase in both volume endurance and pressure resistance exercise, while the referees mainly practiced endurance training 13.

This observation may explain the morphological differences between the players' and referees' left ventricular mass.

The present results are in partial disagreement with those of Castagna et al. 1415, who studied the performances of referees of different age-groups and reported no differences in the 12-minute running test, whereas speed and acceleration tests were significantly better in the younger referees. However, the focus of the present investigation is on cardiac morphology at rest and systolic and diastolic function.

Finally, general performance in athletes is due not only to the contractile function of the heart, but also to complex interactions with the neurological and muscle-skeletal systems.

Our unpublished personal data on élite soccer players (ACF Fiorentina Football Team) have in fact showed that functional performances differed even among players whose cardiac mass was equal. The athletes followed the same training program.

This investigation has focused exclusively on cardiac morphology, and thus presents no functional correlation with maximum oxygen consumption and endurance, speed and strength performances.

Athletes between 35 and 40 years can maintain a good performance in both short- and long- distance running. However, even if these important parameters progressively decrease with age, with peak decrease occurring at about 50 years, performance is not dramatically impaired when the athlete is 40 years old. 1617.

These results are supported in the literature by the study of Rotoyannis and Korhonem, who demonstrated that 35–40 year-old athletes are able to maintain good performance in marathon runs up to 50 Km, or sprints up to 100 m 18192021

Finally, it would be interesting to conduct a longitudinal study on referees entering the first division. It is in fact important that a referee's physical performance should not decrease, in order also to guarantee the psychological aspects of refereeing, which are certainly improved with specific experience within the sporting context.

The author(s) declare that they have no competing interests.

The initial idea for the study was of GG. GG, AP, ML, LS and AM designed the study, and GG, LS, LT and AM performed all the measurements and statistical analyses. GG wrote the manuscript and all the authors contributed to, read, and approved the final version.