Table 1 Studies focused on match indicators

Catterall et al. [109]

Referees covered 8–10 km, significantly less distance during the second half compared to the first half. The mean heart rate was 165 beats per minute, corresponding to 95% of the maximal heart rate. Jogging, walking and running backwards were the most common activities during the game. 1.1 km was covered sprinting

Training programs should include aerobic and anaerobic activities

Johnston and McNaughton [110]

Soccer referees covered, on average, 9.4 km per game, which included walking (18.9%), jogging (46.6%), running/striding (12.1%), sprinting (6.2%) and backward movements (16.2%). Most of the time was spent at low intensity (65.5%), but the heart rate was above 85% of the maximal heart rate without differences from the first to the second half

Training programs should include aerobic and anaerobic activities

D’Ottavio and Castagna [111]

Referees spent 17.2% of the total match in high-intensity activities (sum of actions faster than 18 km⁻¹). Differences between the first and second half were considerable. For example, referees covered less distance during the second half on medium-intensity runs, walking forward and walking backwards and spent more time standing. However, the high-intensity distance was comparable, and the total distance covered during the first and second half was 5854 m and 5612 m, respectively

Training programs should combine aerobic and high-intensity activities in training programs—maximal intensities should not exceed 30 m

D’Ottavio and Castagna [11]

The mean heart rate was 163 beats per minute (89.1% of the maximal heart), and no changes were noted between the first and second half. Approximately 42% of the time was covered at velocities higher than 13 km h⁻¹

The internal and external load analysis showed the intermittent pattern of soccer activities in referees. The time of sprints ranged between 2 and 4 s

Krustrup et al. [34]

The distance covered during a match was approximately 10 km: 3.87 km walking, 1.94 km jogging, 1.69 km low-speed running and 1.67 km high-intensity running. The last parameter decreased from the first to the second half. Distance from infringements was, on average, 11 m, increasing from the first to the second half. Mean heart rate and blood lactate were 162 beats per minute (85% of maximal heart rate) and 4.9 mmol l⁻¹, respectively. The total high-intensity activities were related to the distance covered in YOYO protocol. The intermittent exercise intervention had an impact on the high-intensity distance covered (after: 2.06 ± 0.13 km; before 1.69 ± 0.08 km) and heart rate (after: 159 ± 1 beat per minute; before:164 ± 2 beats per minute)

see match indicators × testing and Table 2—interventions section

Krustrup et al. [13]

The distance covered by the assistant referees was, on average, 7.28 km. Low and high-intensity running activities corresponded to 19.3% and 4.1% of the total time. Distances covered walking, jogging, low-speed running, backwards running and sideways running were 3.1 km, 1.0 km, 0.8 km, 0.06 km and 1.16 km, respectively. The mean heart rate during the match was 173 beats per minute (73% of maximal heart rate). Blood lactate was 4.7 and 4.8 mmol l⁻¹ after the first and second halves. Maximal oxygen uptake was, on average, 3.71 l min⁻¹

Aerobic and anaerobic activities are part of assistant referee activities. Sideways and forward running combined with intermittent exercise training need to be included in training programs

Castagna and Abt [98]

Considering different distances covered during matches (short vs. long), no differences were reported in high-intensity activities. Increments in submaximal activities determined the distance covered on long matches. This issue also highlights the importance of high-intensity activities in short and long matches

Soccer referees should include aerobic activities as well high-intensity intermittent exercises

Castagna et al. [101]

International referees (approximately 11 km) covered less distance than national referees (approximately 13 km) and also performed less distance at velocities faster than 18 km⁻¹

Given the relationship between distance covered and positioning during the match, training programmes for international soccer referees need to be adjusted

Helsen and Bultynck [112]

The mean heart rate for referees and assistant referees was 155 and 140 beats per minute, respectively, corresponding to 85% and 77% of the maximal heart rate. Among referees, during the match, the percentage of maximal heart rate tends to increase in the first and second half. In contrast, in assistant referees, heart rate tended to decrease in the first half, which is maintained relatively stable during the second half. Most of the total time was spent in maximum efforts and high-intensity activities, while assistant referees spent most of the total time in low-intensity activities. Referees made 137 observations per game

High-intensity intermittent protocols should be part of training programs—aerobic components should be prioritized. Additionally, video analysis should also be included in training programs

Weston et al. [113]

A significant relationship between heart rate and rate of perceived effort was significant. In parallel, heart rate and perceived effort were significantly higher in Premier League soccer referees compared to Football League. Within each league, referee experience did not affect heart rate and rate of perceived effort

The results of this study showed that heart rate and rate of perceived effort were valid measures of match intensity

Weston et al. [5]

The values of high-intensity running and total distances reported in the first half were related to the values of the second half. No significant changes in these parameters were noted across the season. Match-to-match variation revealed that referees covered less distance at high-intensity running during the second half

Match activities of soccer referees are related to player demands. An appropriate schedule should be created in order to permit an appropriate recovery from match to match

Mallo et al. [36]

Assistant referees covered, on average, 6.1 km per game. Comparisons between the first half and second half revealed that distance tends to decrease from the first (3.2 km) to the second half (3.0 km). Regarding match-specific activities, assistant referees were 56.9% of total playing time still and 24.1% walking. In addition, 1.4% of playing time was spent sprinting. During the second half, assistant referees passed more time still and decreased the time spent jogging and running. Sideway movements were frequent in assistant referees (30% of the total distance). Distance from offside situations (n = 81) was, on average, 1.36 m

Specific training sessions for assistant referees should be developed

Krustrup et al. [89]

Referees and assistant referees differed in total distance covered (referees: 10.3 km; assistant referees: 6.8 km) and high-intensity running (referees: 1.9 km; assistant referees: 1.0 km). A considerable distance of backward running was noted for referees (0.9 km), while assistant referees tended to perform sideways running (1.5 km). The mean heart rate was higher for referees than assistant referees; no difference was found in blood lactate. High-intensity running did not decrease across the games, and this parameter was related to the distance from infringements

High-intensity running was frequent among international referees. The current study noted substantial differences in match performance between referees and assistant referees, and this point needs consideration in developing training programs

Mallo et al. [22]

The mean distance covered during the games was 10.2 km. The total ball distance covered was partially related to high-intensity activities and the total distance covered by the referees. In the current study, the mean heart rate was 161 beats per minute, corresponding to 86% of the maximal heart rate. Mean heart rate is not helpful—comparisons between high-intensity efforts and heart rate should be adjusted for narrow intervals (i.e. 5 min). Based on 304 incidents, the mean distance was 16.3 m

The activity is related to the distance covered by the ball and, consequently, by the playing style of each team. Heart rate analysed in narrow intervals is a good tool for determining high-match intensity

Mallo et al. [23]

Assistant referees covered, on average, 5.8 km and spent 29.7% of playing time in sideways movements. Compared to data from the under-17 World Championship 2003, assistant referees of the Confederations Cup covered more distance at higher speeds. Ball distance was related to the distance covered by the referees and the frequency of high-intensity activities. Distance from the offside line was, on average, 0.64 m, and the mean heart rate was 140 beats per minute

Team playing style, as well as competitive level, influence the activity of assistant referees

Catteeuw et al. [114]

From 4960 offside situations, 868 (17.5%) situations were marked as errors (737 non-flag errors and 95 flag errors). Considering six 15-min match periods, the error distribution is constant across the game. No significant associations were noted between the errors and the assistant referee position in relation to the offside line and movement speed. Note that most of the offside decisions were taken walking or jogging. The optical error hypothesis (position of attacker and referee about the second defender) was not confirmed, and non-flag errors were observed in flash-lag situations

Decision-making training can be helpful using defenders and attackers on the field. Another essential tool is video feedback, and off-field offside decision-making tests and programs need particular attention

Mallo et al. [107]

The distance covered by the assistant referees was 5.6 km, and sideways movements were the most representative activity during the soccer match (26.6%). High-intensity activities (velocity > 13 km⁻¹) accounted for 2.0 km, and the frequency of actions was stable across the matches. The distance from the offside line was, on average, 1.06 m

Male and female assistant referees are comparable in terms of match activity patterns. Since the distance from the offside line is similar across the game, the results of this study indicated that female assistant referees involved in the under-20 Women World Championship could maintain the pace during the match

Mallo et al. [108]

Female referees covered, on average, 10 km per match. The mean distance decreased from the first half (5.2 km) to the second half (4.9 km). 25.7% of the time is spent walking, while medium-intensity activities (i.e. jogging) accounted for 21% of match time. High-speed activities accounted for 6% of the total time. No differences were noted from the first to the second half. No variation was noted in the distance from incidents and ball position from the first to the second half

Female referees physical demands are closely related to male referees (moderate competitive level). The female participants that participated in the under-20 Women World Championship maintained the pace of the game

Weston et al. [20]

Total distance covered during the match, high-intensity running and sprint frequency negatively correlated with age. On the other hand, the distance from the ball and fouls were not related to age

The reduced physical match activities associated with increasing age did not impact the positioning of referees. Consequently, the age of retirement (45 years old) should be reviewed

Di Salvo et al. [115]

Referees and assistant referees covered, on average, 11.6 km and 6.5 km. Jogging and high-speed running were performed less during the second half. The walking activity was frequent in the second half compared to the first half

Although variation across competitions has been noted, the present study confirms the importance of short-maximal intensities among soccer referees

Weston et al. [100]

Match activities (total distance, high-speed running and sprinting) decreased from 0 to 15 min of the first half to the start of the second half (46–60 min) in soccer players and referees. A decrement in the technical performance of referees expressed as the distance from the ball was noted. Distance from fouls and the number of decisions were stable

Match activities of soccer players and referees were comparable. It was assumed that a slower tempo of the match caused reduced match activities during the initial phase of the second half

Weston et al. [106]

Variability on match to match was observed for high-speed running distance, recovery time, percentage of explosive sprints and the total number of sprints and fouls. The match-to-match variability was reduced for total distance covered, top sprinting speed and distance from fouls and the ball. Age and referee experience did not influence match-to-match variation

Given the greater variability between matches, future studies must include larger samples. In parallel, conditioning training should be adequate in order to prepare older referees for the demands of the game

Weston et al. [116]

Soccer referees covered 11.3 km, while players accounted for 10.8 km. Regarding the mean total distance covered, high-speed running and sprinting were comparable among soccer players and referees. Considering the entire season, total distance and sprinting were similar between players and referees

Activities of soccer players were related to referees. Soccer referees fit the needs of the game

Barbero-Álvarez et al. [97]

Field referees covered, on average, 10.2 km, while assistant referees covered 5.8 km. Regarding the frequencies of actions, no differences were noted between referees and assistant referees; however, the distance covered in accelerations was superior for field referees. Field referees tended to decrease the number of accelerations from the first to the second half, while no significant differences were found among assistant referees. heart rate, Mean expressed as the percentage of maximal heart rate, was 85.6% and 75.3% for referees and assistant referees, respectively. Curiously, the distance covered by field referees correlated with the maximal rate percentage. The effective index decreased significantly in the first half and the second half in referees. The decrement in assistant referees was noted in the second half

Acceleration activities should be part of soccer referee training programmes. The effective index needs to be considered for examining changes in performance

Mallo et al. [117]

The errors of referee and assistant referees were, on average, 14% and 13%, respectively. Among referees, the lowest percentage of error occurred in the central area of the field. The angle of vision, particularly 46 and 60o, is a crucial variable in decreasing the percentage of errors. Otherwise, the distance from the offside line was unrelated to the offside decisions. The highest error percentage tended to occur towards the end of the matches

Perceptual-cognitive demands of the game should be training among assistant referees. Additionally, the performance of assistant referees should be expressed as a percentage of successful decisions

Costa et al. [118]

No differences in the distance covered in the first (5.2 km) and second half (5.2 km) were noted. Most of the time was covered at ≥ 80% of the maximal heart rate. Subjective (rate of perceived effort) and objective (Edwards method) were associated. Significant correlations between the rate of perceived effort and distance covered at 90–100% of maximal heart rate and maximal speed were noted

GPS and heart rate monitors are helpful tools for monitoring training load. The current study highlights the need for high-intensity training programs for referees, and the rate of perceived effort is a valuable tool to control the internal load

Barberó-Alvarez et al. [119]

The present study defined repeated sprint sequences (3 consecutive accelerations—> 1.5 m s⁻²—interspersed with a maximum of 45 s of recovery) and repeated sprint ability (3 consecutive sprints—> 18 km h⁻¹—interspersed with a maximum of 45 s of recovery). Note that referees and assistant referees spent 37% and 20% of the total distance in accelerations, respectively. From the first to the second half, referees decreased repeated acceleration activities

This study clarified the concepts of sprint and acceleration. Hence, acceleration testing should be part of referee programs

Gomez-Carmona et al. [120]

The current study analysed one main referee and five assistant referees in 4 matches. The referee had, on average, 179 beats per minute, corresponding to 68% of the maximal heart rate. 56% of the live time was spent at 85–95% of maximal heart rate. On the other hand, the assistant referee spent most of the time between 85 and 95% of the maximum heart rate—the mean heart rate was 139 beats per minute. Distances covered differed between referee (~ 10 km) and assistant referees (~ 6 km), as well, on match activities. Overall, errors tended to occur between 85 and 95% of maximal heart rate, and a higher percentage of error was noted on the right side of the soccer field (79%)

The authors did not present practical applications and compare the results of this study with the literature

Castillo et al. [121]

Differences between referees and assistant referees were found on match load. More specifically, referees reported higher values of internal and external loads. Regarding internal load, differentiated ratings of perceived respiratory and leg muscle were noted, with referees reporting higher values than assistant referees. The association between internal and external loads was not evident

Referees and assistant referees need to be involved in sessions with different characteristics. The present study highlights the importance of controlling internal and external loads

Dolanski et al. [122]

Referees ran 7.75 km, while assistant referees covered 4.40 km. On average, mean heart rate, maximum heart rate and mean velocity was significantly higher in referees than in assistant referees. Maximum velocity was higher in assistant referees

Referees and assistant referees require specific preparation

Fernández Elías [123]

Referees covered approximately 8.7 km. No differences were noted among distances and heart rates measured during the first and second half. Maximum velocities attained were 26.0 and 26.5 km h⁻¹ in the first and second half, respectively

Strength and aerobic sessions are essential to referees

Castillo et al. [102]

In general, referees that participated in best team matches covered more distance walking (velocity defined as < 3.6 km h⁻¹) and performed more accelerations and decelerations than referees who participated in lower team matches. Considering internal load parameters, referees who participated in mixed matches reported lower values of maximal heart rate. The same participants reported higher respiratory and muscular perceived match load during the second half

Short-term actions need to be considered in training programs that involve referees from higher competitive levels. The rates of perceived match load in the second half suggested the onset of fatigue

Joo and Jee [99]

Comparable match intensities (distance covered, jogging, running and sprinting) were noted among referees and players. The number of fouls, the distance between fouls and referee positioning, and foul errors were significantly higher after the 75-min. The frequency of errors tended to be higher at the locations farther away from the assistant referees

Training sessions should include perceptual and cognitive tasks to improve foul decisions

Ozaeta et al. [124]

During the second half, lower values of mean power, mean speed, mean cadence and mean and peak heart were reported among referees. They presented lower mean and peak heart rate values during the second half. However, the analysis by 15-min intervals revealed that referees covered more distance 75–90 min and performed higher mean power. Of interest, the mean heart value tended to decrease in the second half and peak power, mean velocity, mean cadence and mean vertical oscillation was higher during the first 15 min of the match

This study demonstrated that match load decreased during the game related to neuromuscular fatigue. However, during the last 15-min match load tended to increase due to team strategies

Castillo-Rodriguez et al. [103]

Physiological responses, determined by heart rate parameters and rate of perceived exertion, were higher in national referees. Differences between groups were also noted for match activities. For example, national referees covered greater distances and spent more time > 13.0 km h⁻¹. Before the game, national soccer referees showed higher self-esteem and self-confidence values and presented lower cognitive and somatic anxiety values than non-national referees. A negative relationship between self-confidence and physical parameters was found. In addition, self-esteem was positively related to high-intensity activities. Finally, age was explained, and psychological responses explained 20–7.7% of referee categories

Prior to the games, national referees had better psychological responses. Physiological programs to improve the rates of chronic anxiety, somatic anxiety, self-confidence and self-esteem must be considered, especially among referees of lower categories

Moreno-Perez et al. [105]

Match congestion impacted match activities—running speed at 21–24 km h⁻¹, > 24 km h⁻¹, frequency of sprints and distance covered at sprint decreased moderately. Although other parameters decreased during match congestion, an interaction between congestions and halves was not found

The present study suggested specific conditioning and recovery programs during match congestion. The current also has implications for referee appointments

Martínez-Torremocha et al. [104]

Comparisons between first and second-division referees noted significant differences in mean heart rate (first division: 146 beats per minute; second division: 153 beats per minute and rate of perceived effort (first division: 7.22; second division. 7.82). Distance covered was comparable between first and second-division referees; however, different match activities were noted. Contrasting match activities by competitive level and considering the first and second halves, it was found that second-division referees showed a decrement in maximum acceleration, sprint distance per minute, maximum velocity and mean heart rate

Match characteristics and demands were different in the two different divisions. Consequently, training programs should be adapted according to the competitive levels