Table 2 Studies focused on testing and interventions

Load × field tests

Castagna and D’Ottavio [11]

Referees covered approximately 11.6 km per game (varied between 10 and 12 km). A significant relationship between maximal oxygen uptake and total distance covered was noted. Additionally, negative correlations between maximal oxygen uptake and time standing were obtained. Overall, maximal oxygen uptake impacts the total distance covered and match intensities

Aerobic power combined with match skills should be the primary purpose of soccer referees training

Krustrup and Bangsbo [34]

The total high-intensity activities were related to the distance covered in the YOYO protocol

YOYO is a valid alternative to test match performance

Castagna et al. [35]

Velocities at 2 and 4 mmol l⁻¹, obtained from a field protocol, were 10.9 km.h⁻¹ and 13.6 km h⁻¹, respectively. Velocity attained at 4 mmol⁻¹ was associated with the total distance covered during the soccer game. However, it was not related to high-intensity activities

The velocity at the blood lactate threshold of 4 mmol l⁻¹ helps to develop training programmes among referees

Castagna et al. [12]

Associations between field protocols (50-m sprint, 200 sprint and 12-min run) and match activities were poor and moderate. In fact, 12-min run test had a positive and moderate association with distance covered at high intensity

The 12-min run test should be used to monitor aerobic fitness. Given the level of referees included in this study, a benchmark of 3 km was defined as an advisable aerobic fitness level

Krustrup et al. [13]

Significant correlations between high-intensity running and repeated sprint test, maximal oxygen uptake and 50-m sprint were found. Meantime, no associations were found between 12 min of running or treadmill protocol with high-intensity activities during the game. Significant relationships between the distance to the offside line and time to complete three sprints after the game and the best trial of the 50-m sprint were obtained

(see match indicators)

Tessitore et al. [14]

On average, the maximal oxygen uptake was 51.8 ml kg⁻¹ min⁻¹, and the mean heart rate was 194 bpm, corresponding to 98% of the maximal heart rate. High-intensity activities (86–95% of maximal heart rate predominantly occurred during the first half). Blood lactate tended to be predominantly elevated after the first half. The performance regarding jump ability showed no significant differences before the match, after the first and second halves

Referees had lower values of maximal oxygen uptake compared to soccer players, probably because they have lower training volume. Referees with adequate fitness levels can maintain performance during the match

Mallo et al. [36]

The reference values for the 12-min running test and the 50-m sprinting were 2962 m and 6.89 s, respectively. Note, no significant association were found between field protocols and match performance

Adequate fitness tests, such as YOYO intermittent interval test and 30- to 40-m sprinting, need future consideration

Mallo et al. [22]

The protocol adopted to evaluate physical capacity (6 × 40 m) did not significantly predict match activities

Protocols adopted by FIFA were poorly related to match analysis parameters

Weston et al. [37]

Associations between FIFA protocols and match parameters were found—the fastest 40-m sprint and distance covered were related to high-intensity running and sprinting distance. In addition, the mean time 6 × 40-m sprint test was associated with the total distance covered, high-intensity running and sprinting distance. On average, the fastest 40-m sprint time was 6.92 s, and the mean of the respective protocol was 5.71 s. Referees covered, on average, 11.5 km

The 6 × 40-m sprint test and, in particular, the fastest sprint is appropriate to assess the physical fitness of soccer referees

Castillo et al. [38]

Referees and assistant referees did not differ on the straight-line sprint test (SLST); however, significant differences were noted in the maximum speeds during official matches. Additionally, among referees and assistant referees, the maximum speed attained in the game was significantly lower than the maximum speed registered in the SLST

Velocities of SLST (3 sprints × 30 m) are not comparable with velocities obtained during the games thus, other protocols need to be validated according to match activities

Castillo et al. [51]

After the match, referees and assistant referees tended to increase blood lactate and sprint time, while decrement in jumping performance was unclear

Match-related fatigue was evident in referees and assistant referees

Risser et al. [39]

The change of direction ability test was not related to high-intensity running activity and accelerations among assistant referees. In opposition, 5 × 30-m sprint test was associated with distance in high-intensity running. Match activities and 6 × 40-m sprint test were not associated among referees

Negligible associations between field protocols and match activities were found, which may is explained by the large variability of match-to-match activities. Match performance is associated with other variables rather than field protocols

Castillo et al. [40]

Referees and assistant referees did not differ in physical performance (linear straight sprint test, modified agility t test free and YOYO distance). Linear straight sprint test and distance covered in the YOYO protocol were related to high-speed and high-intensity match activities (coefficients of correlation ranged from moderate to large) among referees. However, linear straight sprint test and high-speed running were associated with assistant referees. Linear straight sprint test was correlated with very high-intensity accelerations and decelerations. Accelerations and very high-intensity decelerations were related to the distance covered in YOYO

External match load was higher in referees than assistant referees, but they had comparable physical conditions. The authors highlighted that training strategies are equivalent for referees and assistant referees. Training sessions of referees should include sprint ability exercises

Preissler et al. [41]

Maximal and mean heart rates during official matches were significantly higher than on field tests. On the other hand, speed parameters (maximum and mean) were higher on physical tests. As expected, the distance covered was also higher in the matches. The percentage of time (70–80% of maximal heart rate) was longer in the match than in the test, while an opposite tendency was obtained for 90–100% of maximal heart rate. Speed zone below 13 km h⁻¹ were longer in the match, while speeding zones above 13 km h⁻¹ (13–18 km h⁻¹; 18–24 km h⁻¹; > 24 km h⁻¹ were longer in the match

Physical tests and match performance require a specific stimulus of training. Before the test, referees are advised to focus their training in anaerobic stimulus, while during the season aerobic training should complement training programs

Physical testing (age variation, competitive level, data quality)

Castagna et al. [45]

12 m run test did not discriminate referees by competitive level. Meantime, top-level referees covered more distance in YOYO protocol than medium and low-level referees. Top referees also show low blood lactate levels determined immediately at the end of the maximal intermittent test

YOYO protocol should be used to select soccer referees

Castagna et al. [15]

A negative relationship between CMJ, 12-min running and age was noted. Although maximal oxygen uptake was higher in the younger group, older referees tend to attain similar velocity at 4 mmol L⁻¹

The present study presented reference values according to age groups: 3030 m (30 years) to 2700 m (42 years); performed 6.90 s and 28 s over 50-m and 200-m sprint tests, Respectively. Referees should also perform VO_2max near 50 ml kg⁻¹ min⁻¹

Casajus and Castagna [42]

Age-associated variation in maximal oxygen uptake, 12-min running test and 200 m were not noted, as well as in body size and composition. Meantime, maximal heart rate and power at the ventilatory threshold were significantly higher in younger referees compared to older peers

Training programmes should include aerobic and anaerobic activities. In order to maintain acceptable aerobic performance, older referees need to assess body mass and composition

Caballero et al. [17]

Two field tests were used: 6 × 40 m and 2 km running. In the first test, the mean time was 5.53 s, while the best sprint was, on average, 4.99 s. 2 km was completed in 7 min and 43 s

Performance expressed by 2 km showed a lower association with VO_2max. Thus, it is not recommended to assess physical fitness

Castagna et al. [46]

The best time of CODA (change of direction ability test) was 9.81 and 9.66 s for the first and second visions, respectively—no statistical differences were noted between groups. No differences were not noted for the mean performance. The protocol did not discriminate competitive level. The intra-class correlation coefficient and technical error of measurement were 0.90 and 0.18, respectively

Percentiles for the current test estimated a cut-off value of ≤ 9.67 s as acceptable. The protocol was reliable and should be considered in test protocols

Castagna et al. [8]

The intermittent endurance test was reproducible, discriminating assistant referees from different competitive levels, and was related to YOYO and VO2_max

The intermittent endurance test seems to be a proper protocol for assessing the intermittent endurance capacity among assistant referees

Castillo et al. [43]

Field protocols did not discriminate referees and assistant references, nor national and provincial referees. Younger referees (≤ 35 years) were faster in sprint and agility protocols and, in addition, covered more distance in the YOYO test. Agility and linear velocity tests were related

Linear sprint tests did not discriminate referees according to the competitive level. Given the age-associated variation in field protocols, training programs should be focused on maintaining agility, acceleration and aerobic capacity in referees, particularly at older ages

Yanci et al. [125]

Modified Agility Test time was higher in regional referees, while differences between national and regional referees were not found for linear sprint protocols (5-m and 15-m sprint tests)

Modified Agility Test can be used to discriminate referees by competitive level

Castillo et al. [18]

During the preparatory period, referees and assistant referees tend to decrease sprint performance assessed by 20 and 30-m tests. On the other hand, referees increased 13.11% the distance performed on the YOYO protocol, while assistant referees decreased 3.36% the distance on YOYO test

Acceleration exercises and lower limb power training need to be implemented among referees during the off-season. In parallel, aerobic sessions during the off-season among assistant referees are needed

Gianturco et al. [47]

The foot posture index (assessed by a questionnaire) was associated with the performance on the YOYO test

The foot posture index, a reasonable indicator of function, needs to be considered in training sessions

Sanchez-Garcia et al. [48]

The total distance covered on the YOYO protocol was only moderately associated with the maximum velocity obtained in the 40-m sprint test. The maximum velocity obtained in the 40-m sprint test and YOYO distance were unrelated to the time to cover 40 m

YOYO protocol seems to have limitations in assessing high velocities

Meckel et al. [44]

Second-division referees were significantly faster in ideal and accumulative sprint times than first-division referees at the beginning of the season (baseline) and mid-season assessment. In addition, second-division referees improved their performance from the baseline to the mid-season. Among referees, age was significantly related to ideal sprint (r = 0.63) and total sprint time (r = 0.66)

The highest level of soccer referees may be explained by something other parameters than physical performance. Experienced referees adopted skills (e.g. positioning, anticipation, decision, running economy) that compensate for physical disadvantages. Younger referees should focus their training plans on tactical drills, while older referees need to focus their training plans on physical capacities

Muscella et al. [16]

Sprint time (40-m test) tended to decrease across the season, while the distance in the YOYO protocol increased. Age was negatively associated with changes on the 40-m sprint test and distance covered on the YOYO protocol. Younger referees showed a higher ranking than intermediate (21–29 years) and older (30–45 years) referees

This study showed that young referees attained better sprint performance and were ranked top

Romano et al. [126]

The 6 × 40-m sprint (best sprint) was positively associated with time to complete an agility test. In contrast, the relationship between the 6 × 40-m sprint (best sprint) and with YOYO protocol was significant but negative. Moderate associations between hand-grip strength and YOYO test were obtained

Hand-grip test and Illinois agility tests are valid alternatives to monitor fitness among referees

Muscella et al. [96]

Across the season, players substantially improved the 40-m sprint test and distance covered in the YOYO test. Changes in cortisol and testosterone were particularly noted from the beginning of the season to the first moment of assessment (8 weeks from baseline) and then systematically decreased until the end of the season (June), attaining the baseline levels. On the other hand, testosterone increased eight weeks from T0 until mid-season and then decreased towards initial values. At moment 1, cortisol and testosterone were related to distance covered on YOYO. At the moment 2, only testosterone was associated with distance covered on YOYO protocol

Referee training promotes physiological adaptations that can be examined by changes in testosterone and cortisol levels. These parameters can be indicators of training adaptations and overtraining

Castagna et al. [49]

YOYO distance covered tended to increase across the 15 months of observation. On the other hand, the time to complete the linear sprint ability test, 5 × 30 m (best sprint) and change of direction protocol increased from the baseline. A very large correlation was noted between the linear sprint ability test and 5 × 30 m (r = 0.89). Intra-class correlation coefficients for the protocols ranged from good to very large.

Given the association between 5 × 30 m (best sprint) and repeated sprint ability and the lower variability in best sprint obtained from 5 × 30 m, a single maximal sprint in of referees may provide the same level of information as repeated sprint ability protocol. Repeated sprint ability and linear sprint tests consider two different types of neuromuscular performance

Interventions

Krustrup and Bangsbo [34]

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)

A high-intensity intermittent protocol (long-duration running intervals: 4 × 4 min or 8 × 2 min; short-duration running intervals: 16 × 1 min or 24 × 30 s) improved performance during the game

Weston et al. [54]

No differences between track and pitch in the mean percentage of maximal rate were noted. However, the maximal heart rate was significantly higher during the track training sessions. After applying high-intensity intermittent training, the mean distance covered in the YOYO protocol increased from November until March

The present study shows practical training sessions for elite referees (see p.56) to improve fitness levels

Boullosa et al. [50]

Moderate to large correlations were found between resting heart rate variability and the rest-to-match day. YOYO test was not correlated with heart rate variability

Cardiac autonomic control decreased in the 5 h before the match until 10 h after the match. In parallel, referees with greater variability on a rest day may tolerate the stress before, during and after exercise. Heart rate variability should be used to assess stress (physical and physiological) and recovery in soccer referees

Castillo et al. [51]

After the game, decrements of 15-m and 30-m sprint tests were noted among referees and assistant referees. After the game, referees and assistant referees increased blood lactate. Differences between groups were found

The current study suggested that soccer matches caused fatigue. Sprint exercises should be part of training sessions

Castagna et al. [127]

The training rate of perceived effort showed no differences immediately after training. Thirty minutes post-training, 7 h post-training and 20 h post-training

The present study showed no significant differences in recall timing on post-exercise RPE when athletes are familiarized with the scale

Castillo et al. [52]

Soccer referees improved jumping performance (different variables were analysed) after the matches

Soccer matches did not cause decrements in vertical jump performance, indicating that neuromuscular fatigue caused by the matches is insufficient to modify jump variables

Yanaoka et al. [58]

The distance covered on the YOYO protocol was significantly longer in the re-warm-up group than in the control trial. After the intervention, no trial × time effect was noted on plasma glucose, fat-free serum acids, serum triglycerides, blood lactate and creatine kinase. As expected, the perceived effort rate was higher in the re-warm-up group

Re-warm up is an effective method to improve performance, although the results of the current study were limited to the YOYO protocol. The present study proposes the following intermittent halftime protocol: 2.15 min of seating rest and 2.15 min of running at 70% of maximal heart rate

Maslenniov et al. [55]

After applying the experimental protocol (p.10, Fig. 2 in the original manuscript), negative classifications decreased in the experimental and control groups. The total distance covered was higher in the experimental group

The authors suggested including physical tests in the annual cycle of soccer referees

Muniroglu et al. [56]

The flag had a negative impact on sprint protocols (5, 10, 20 and 30 m) among assistant referees. The initial position of referees (straight or lateral) did not influence the performance in field protocols. Training with a flag promoted substantial performance improvements

Assistant referees should include a flag during training sessions to improve speed

Baydemir et al. [57]

After a 16-week intervention of high-intensity interval training and sprint sessions, referees significantly decreased body mass and improved the performance on FIFA protocols (40 × 75 m; 6 × 40 m) and the Cooper test

The current study showed a training cycle positively impacting FIFA (6 × 40 m) and Cooper protocols among amateur referees

Fernandez-Ruiz et al. [53]

Soccer matches did not influence isometric knee flexion strength in the dominant limb but the isometric body strength of the non-dominant limb among referees. Differences were noted in assistant referees. Differences after the match were negligible in the range of motion of hip flexion in dominant and non-dominant limbs in both groups

Strength programs need to be developed for referees in order to reduce differences in isometric hamstring strength after the match