Table 4 Studies focused on physiological outputs

Galanti et al. [78]

No differences were noted between soccer and referees in the following parameters: left ventricular mass, aortic root diameter, left ventricular diastolic dimension, septum and posterior wall thickness

In general, the comparisons of this study suggested comparable heart dimensions between soccer players and referees

Caballero et al. [79]

The rest heart rate was, on average, 59 beats per minute. Linear measurements of the systolic diameter of the left ventricle, the diastolic diameter of the left ventricle and the diameter of the left atrium were 33.7 mm, 50.0 mm and 29.8 mm, respectively. In addition, the thickness of the left ventricular septum was 9.77 mm, and the posterior wall of the left ventricle was 9.47 mm. The mean diastolic volume of the left ventricle was 135 ml, and ejected volume was, on average, 47.3 ml. Estimated left ventricular mass ranged 86–349 g, and the mean value was 219 g

Echocardiography parameters indicate an increase in the cardiac chambers and average values for the thickness of the walls. Hence, the increased size of the ventricle explains the left ventricular mass

Caballero et al. [17]

Biochemical parameters were obtained for haemoglobin (14.9 g dl⁻¹), iron (87.5 g dl⁻¹), ferritin (85.1 g dl⁻¹), transferrin (276 g dl⁻¹) and red cells (4.9 μl). Linear measurements of the left ventricle were 34.8 mm, 51.2 mm, 9.8 mm and 10.1 mm for systolic diameter, diastolic diameter, posterior wall and septum thickness. Left ventricular mass was, on average, 122 g. VO_2max evaluated during an incremental treadmill test was, on average, 48.7 ml kg⁻¹ min⁻¹, while the maximal heart rate was 190 beats per minute. The mean heart rate at the second ventilatory threshold was 175 beats per minute, corresponding to 92.7% of the maximal heart rate

Blood parameters did not match with aerobic training parameters. With this in mind, the authors recommend frequent assess of haematological parameters

Silva et al. [81]

Referees were, on average, older, fatter and had lower values of VO_2max than soccer players. No differences were found in height and weight

FIFA battery needs to include tests to assess aerobic power. Additionally, nutrition guidelines should be developed in order to improve the athletic profile

Palmer et al. [86]

Absolute and relative torque development at ½ and ¾ of maximal voluntary contraction of the hip and thigh posterior muscles were higher in full-time referees than part-time referees. No differences between groups for peak torque and maximal power were noted

The current study shows that the isometric extension of the hip allows discriminating professional and semi-professional referees. Consequently, training programs should include exercises to increase relative torque development of the hip and thigh

Mazaheri et al. [82]

Cardiorespiratory parameters were, on average, 159 beats per minute and 59.94 ml kg⁻¹ min⁻¹. The physiological parameters examined in this study, VO_2max and forced vital capacity, were not related to the mean score assigned for each referee

Body composition and physiological parameters were not associated with referee scores. Thus, cognitive aspects, psychological factors and experience may explain performance

Castagna et al. [83]

Male and female referees differed significantly on aerobic outputs—male and female referees attained a respiratory exchange ratio of 1.20 and 1.09, respectively. Female referees VO2max (48.1 ml kg⁻¹ min⁻¹) was significantly lower than in males (51.9 ml kg⁻¹ min⁻¹), and the peak velocity on the treadmill. After scaled body mass, only one female referee presented VO_2max higher than the mean value of male referees

In order to promote female referees in male competitions, female referees need additional aerobic training

Coffi et al. [80]

At baseline, 51.3% of soccer referees showed normal heart geometry, 37.8% presented concentric remodelling, 8.1% exhibited eccentric hypertrophy, and 2.7% had concentric hypertrophy. After the championship, the participants who presented ventricular hypertrophy did not substantially differ in heart morphology

Structural and functional parameters of the heart were classified as usual among referees

Talovic et al. [87]

Premier league referees of Bosnia and Herzegovina presented higher values on total work than first league referees. The ratio of non-dominant knees indicated that Premier League referees had a higher ratio than first league referees (3.7%)

Asymmetry and total work discriminated referees by competitive level

Castagna et al. [84]

Maximal oxygen uptake, expressed in absolute terms, was significantly higher in referees (3.98 l min⁻¹) than in assistant referees (3.64 l min⁻¹). Differences between groups were attenuated when maximal oxygen uptake was expressed by body mass, as well as on maximal aerobic speed and speed to exhaustion. Differences in running efficiency were negligible between groups. The speed at the ventilatory threshold was near 14 km h⁻¹. At the ventilatory threshold, heart rate, expressed as a percentage of the maximal value, was 91% in referees and assistant referees. The analysis in the present study developed cut-off values for aerobic parameters—maximal oxygen uptake (3.93 l min⁻¹; 50.6 ml kg⁻¹ min⁻¹), peak treadmill speed (16.8 km h⁻¹), the ventilatory threshold at maximal oxygen uptake (42.6 ml kg⁻¹ min⁻¹), blood lactate (10.8 mmol l⁻¹)

The similarities in training programs may explain comparable values on aerobic parameters among referees and assistant referees. The authors suggested that aerobic training (to improve maximal oxygen uptake) should adopt short intervals (15 s to 2 min), and the heart rate should be above 95% maximal heart rate

Santos-Silva et al. [85]

Significant differences between soccer players and referees were found for age (referees: 34.8 years; players: 20.8 years), maximal oxygen uptake (referees: 54.7 ml kg⁻¹ min⁻¹; players: 58.8 ml kg⁻¹.min⁻¹) and maximal heart rate (referees: 184 beats per minute; players: 192 beats per minute). No differences were found between groups in other relevant aerobic parameters, mainly velocity at maximal oxygen uptake, the velocity at the second ventilatory threshold, percentage of maximal oxygen uptake at the second ventilator threshold and respiratory exchange ratio

Aerobic assessment should be required in international referees rather than age alone