Global positioning systems (GPS) have received increasing use in sport since the first use of GPS to track various physical activities in a single athlete (17). The ability of GPS technology to track player movement simultaneously among multiple athletes is particularly useful in intermittent running sports such as soccer, field hockey, and rugby, where motions such as tackles and changes of direction occur frequently and the most prevalent physical activity is running, with most of the research focus on the analysis of running categories in match analysis including distance traveled, maximal speed, and amount of high-intensity running. Although men's field sports have used GPS for some time, there are limited data available from women's field sports. The use of female-specific data can inform gender-specific training, and increase monitoring of potential injury risk in a population susceptible to running-based injury.
Total distance is a global indicator of external physical load during match play. Distance covered during a time-specific match provides a bench mark for running performance expectations; however, reported total distance is not always comparable because of differences in regulation times between sports and individual playing time due to substitutions. Instead, work rate or relative distance (distance/time, expressed in meters per minute) is used to compare total match effort between different sports and individual players. Table 1 summarizes total distance and work rates during matches from studies reporting match length and total distance traveled.
Among youth soccer players, Vescovi (23) reported a significant difference (p < 0.001) in work rate from under-15 players (86 ± 3 m/min) to under-16 and under-17 players (100 ± 1 and 100 ± 3 m/min, respectively), indicating an increase in running ability in this age range. Recent studies using GPS reported work rates of 100 m/min or higher among elite adult players. Previous video-based motion analysis characterized professional women's soccer work rates from 110 to 116 m/min (1,15). Although high average work rates were still reported using GPS analysis (118 m/min), a wider range from 100 to 120 m/min could more effectively represent target work rates in elite female soccer.
Studies in field hockey reported similar work rates of 98–110 m/min (26) compared with age-matched National Collegiate Athletic Association (NCAA) soccer players (96–107 m/min) (25). Several studies of elite female rugby sevens describe similar work rates (91–117 m/min) (5,16,19,24) to elite field hockey and soccer, highlighting potential common fitness attributes among these field sports at similar participant age and competition level. Similar fitness standards in elite female field sports suggest that aerobic running programming may be generalized for intermittent field sports, with sport-specific focus centering on skill sets and positional differences.
DISTANCE AS AN INDICATOR OF FATIGUE WITHIN A MATCH
Total distance and work rate are useful performance parameters for monitoring fatigue between match periods. Although a reduction in distance or work rate might also be a result of contextual variables, such as match result, opposition ranking, or player formation, (10,27) GPS analysis of substitutes in soccer demonstrates that substitutes into a match had higher work rates in the final 12 minutes of match play compared to players completing a full match, (25) suggesting fatigue is still a confounding variable of the reduction in work rate.
In soccer, fatigue during the second half and particularly in the last 15 minutes of play has been cited as a potential factor of injury risk during the same time period (9). Barbero-Álvarez et al. (2) reported an 8% reduction in distance for the second half in a friendly match with under-13 players. In competitive youth matches, Vescovi (23) found a reduction of approximately 100–150 m (∼3%) in total distance during the second half compared to the first half across all player positions (i.e., defenders, midfielders, and forwards). In elite women's soccer, Hewitt et al. (10) reported a 4.8% decrease in the second half; in particular, distance traveled in the last two 15-minute periods of the game was significantly different than distance in the first 15-minute period. Vescovi and Frayne (26) reported similar work rate reduction patterns of 7–9% in female field hockey for all player positions, despite rolling substitutions.
Reduction in work rate in the second half of competition was reported in rugby sevens for both international- and national-level teams: national-level team average work rate decreased from 103 m/min in the first half to 88 m/min in the second half; international-level team average work rate decreased from 126 to 104 m/min (16) The one published study on women's rugby union demonstrated no reduction in second-half distance, similar to results in men's rugby union (20). Although the data do not demonstrate consistent percentage decrements, current published studies show that decreases in work rate occur regardless of competition level or sport, with the exception of rugby union. Monitoring of fatigue during matches may impact substitution strategy and assist in fatigue-related injury prevention.
ANALYSIS OF HIGH-INTENSITY RUNNING AND SPRINTING
Although work rate is a useful indicator of external work load, it does not indicate the amount of high-speed work performed during a match. High-intensity running (HIR) efforts can be critical to match results, (18) and the amount of HIR and the ability to repeat HIR are distinguishing performance attributes of elite players (1). Sprinting is also a key component of performance in field sports. The ability to sprint faster and for longer distances is a characteristic that distinguishes top-class from lower-level players (15,16) and, as a component of HIR, is similarly critical to match results (1). Maximal speeds during match play are reported in Table 2.
HIR and sprinting have been researched to some depth in female field sports. Dwyer and Gabbett (7) proposed HIR velocity ranges and sprinting velocity thresholds for women's soccer and field hockey, based on normal curves of best fit from average distribution of speed from anonymized elite match data (HIR soccer: 12.2–19.1 km/h, HIR field hockey: 13.3–19.1 km/h, and Sprinting both: ≥19.44 km/h). However, the definitions of high-intensity running and sprinting in published research have still varied greatly. A summary of HIR and sprint thresholds and ranges used in GPS analysis of female field sports is in Table 3.
Researchers argue that using velocity thresholds based on male data will underestimate high-intensity work of female athletes (4,5). In one example, a study of NCAA soccer using a HIR threshold of >13.0 km/h (similar to proposed HIR for female soccer players noted above) and sprinting threshold of >22.0 km/h (higher than proposed sprinting threshold for females) reported 138.41 ± 36.43 HIR efforts but only 4.31 ± 3.51 sprints (mean ± SD) per game. Not only does this underestimate work performed but also underestimates the physiological cost of the work from both aerobic and anaerobic systems.
HIR and the ability to perform above this threshold is an important physiological component of intermittent field sports. As such, practitioners experimented using high-intensity thresholds based on physiological tests. Clarke et al. (5) tested 12 international rugby sevens players for maximal aerobic running capacity (V[Combining Dot Above]O2max test). Researchers used speed at the second ventilatory threshold (V[Combining Dot Above]T2speed) to define high-intensity running. When individual thresholds based on V[Combining Dot Above]T2speed were applied to match running data, distances traveled at high-intensity speeds were highly correlated with HIR capacity. This association declined using a group mean threshold of 12.6 km/h (3.5 m/s). Because laboratory-based V[Combining Dot Above]O2max tests are not always available, Bradley and Vescovi (4) have suggested using 80% of maximal aerobic velocity to estimate the second ventilatory threshold for individualized HIR thresholds. Maximal aerobic velocity can be determined through the use of a range of field-based fitness tests, including a 5-minute time trial and the University of Montreal Track Test (3). However, the use of a group mean threshold would allow for player comparison and comparison between age-matched sports because the reported group mean threshold is similar to the HIR thresholds previously suggested for women's soccer and field hockey (7).
Research has illustrated that players run a large percentage of matches below defined HIR thresholds. (5,25,26) A player's ability to run at low and moderate speeds for long periods can increase overall work rate, highlighting the importance of defining HIR threshold and suggesting that monitoring of player ability to perform sustained low-intensity work could be another component of performance analysis.
Sprinting and the ability to repeat sprinting efforts stress players anaerobically. However, anaerobic capacity varies greatly based on age and competition level. When studying the use of different sprint thresholds in professional women's soccer, Vescovi (22) found that 11% of sprints were in excess of 25.0 km/h, although previous research in soccer and rugby shows that lower-standard players perform significantly less high-intensity work than international or top-class professional players (15,16). If this threshold were to be used for female players at subprofessional levels, the amount of sprinting during matches could be underestimated.
Another key use of GPS analysis is to assess positional differences within a sport. In field hockey and soccer, positions are generally categorized as forwards, midfielders, and defenders. In rugby, positions are broadly categorized as forwards and backs.
One article on international soccer players (10) reported midfielders covering significantly more total distance than defenders and midfielders covering significantly more distance at high-intensity velocities than both defenders and forwards. Both midfielders and forwards covered significantly more distance at sprinting velocities (>19 km/h). A study evaluating sprinting in professional women's soccer matches (22) found that forwards completed more sprints per match (43 ± 10) than defenders and midfielders (36 ± 12 and 31 ± 11, respectively). In NCAA soccer, (25) defenders covered less total distance than forwards and midfielders. Forwards and defenders both covered more distance at sprint speeds than midfielders. In youth soccer, (23) midfielders were found to cover more total distance than defenders, primarily because of more work performed at speeds lower than the HIR threshold. Forwards recorded more distance at sprint speeds and greater peak speeds than midfielders.
In field hockey, positional differences in the women's game are less clear. In one study on elite field hockey, (26) forwards had significantly less playing time than defenders, although total distance between all positions was similar. Defenders performed more low-intensity running and had a lower work rate than forwards and midfielders. Based on mean distance traveled, midfielders ran more during match play, though forwards recorded longer distances at sprint speeds and on average reached higher peak speeds. Gabbett (8) found that on average midfielders cover greater total distances during match play, and also covered longer distances at high-intensity velocities (HIR > 18 km/h). Another study (11) reported defenders covering greater total distances and forwards covering the least, with no differences in mean sprint or high-intensity distance between positions. In a study focusing on sprint performance in field hockey matches, players had similar peak speeds, though forwards recorded higher peak speeds during some matches.
Positional differences were not evaluated in the literature on female rugby sevens. However, in rugby union (comprising teams of fifteen players), backs covered significantly more total distance and ran more frequently at high-intensity speeds than forwards (5.4% versus 1.4% of total time)(18).
Differences in running performance indicators between positions in sport have implications for position-specific training, although these may vary by competition level. In soccer and field hockey, midfielders generally run the length of the pitch, switching between defense and offense, so it would seem logical that midfielders cover a greater total distance. Forwards in soccer and field hockey tend to sprint faster and more often than other positions. Defenders might not demonstrate high total distance or high sprint distances because of opposition movement. Rugby backs are expected to run and pass the ball and to score, and so make frequent runs across the pitch accumulating high total distance. Forwards tend to run shorter distances than backs, instead having a larger strength component for scrums and set pieces. Data from GPS analysis can assist in developing sprint training over sport-specific distances, HIR and repeated sprinting, and aerobic training specific to positions to reflect match demands.
GPS allows for tracking and analyzing movement patterns during training, where training often occurs away from stadium structures and large numbers of sessions make video analysis time-consuming. Only four peer-reviewed GPS analysis studies have evaluated training sessions in female field sports (2 soccer and 2 field hockey).
Gabbett (8) analyzed training sessions of small-sided games and competition performance of an elite women's field hockey team. More low-intensity work occurred during small-sided games compared with competition (∼60% of training time versus ∼35% competition time), and less moderate (10.8–18 km/h) and high-intensity work (>18 km/h). Another study analyzed small-sided training games in field hockey, assessing the effect of team ranking on training status (27). In this study, work rate and team ranking were highly correlated (Pearson's r = 0.95, adjusted R2 = 0.87) with the highest training work rate (∼84 m/min) performed by the top-ranked team; however, high-intensity running did not have the same relationship with team ranking. Future research might investigate the effect of training work rate on team ranking.
Mara et al. (12) used GPS to assess training in an elite female soccer team across an entire season. The durations of training sessions were not provided, though assuming analyzed sessions were of a similar length throughout the season, a decrease in work rate is inferred through the decrease in total distance from preseason to late season (6,646 ± 111 to 4,604 ± 110 m, respectively). This is consistent with expected decreases in training demand because of match scheduling; however, acceleration and sprint performance also decreased throughout the season as monitored through periodic performance tests. Further understanding of training demands and physical performance indicators and the interaction of these variables throughout a competitive season would help inform coaches on effective periodization strategies specific to the female game.
Tan et al. (21) studied the relationship of training demands and hemolysis relating to potential iron store depletion in professional female soccer field players (n = 7) and goalkeepers (n = 3). Training effected a similar hemolytic response in field players and goalkeepers, despite GPS analysis showing field players covering significantly (p < 0.05) more distance and spending more time at higher speeds than goalkeepers. This would suggest that hemolysis occurs because of goalkeeper-specific training demands such as plyometrics, acceleration within the box, tackles, and frequent landing on the ground to save goals that might be quantified through accelerometry in further studies. This study also found that the work rate of field players in training was significantly less than match work rate (74.5 ± 8.8 and 105.6 ± 9.2 m/min, respectively) which is consistent with differences in work rate between training and match play in field hockey (27).
Although small-sided games are meant to replicate match situations, these studies illustrate a possible lack of adaptation from training to appropriately prepare for match play because training efforts do not replicate the physiological demands of matches. GPS analysis could be useful for monitoring, training, and informing coaching and training staff if training goals are being met.
CONCLUSIONS AND PRACTICAL RECOMMENDATIONS
Understanding the requirements of field sport competition is a crucial factor in an effective training program if specific training adaptations are to have an optimal transfer to performance and reduce fatigue and subsequent injury. By understanding average work rates during performance (Table 1), coaches are able to assess an athlete's current level of fitness in relation to the required competition demands. Subsequently, it is expected that on average, female soccer may have greater running demands than other female field sports including field hockey and rugby. The usefulness of designing training based on competition demands may be limited because of the reliance on averaged performance results. Match running demands may therefore be underestimated because of the impact of long active rest periods (walking) on the average work rate calculation. To more accurately reflect match demands, periods of active rest may be removed from the performance duration and work rate determined from periods with a significant physiological demand. Furthermore, it may be possible to convert this newly calculated work rate to meters per second to estimate the level of maximal aerobic velocity required to sustain performance without a rapid onset of fatigue. This combined with the use of GPS to monitor training allows for the creation of drills that replicate a similar intensity to competition.
Furthermore, the understanding of a performance profile (considering HIR and sprinting efforts) can reduce the impact of averaged data and improve training program specificity. However, there is a lack of agreement in the methods used to determine HIR thresholds and sprints within female field sports with some methods informed from the respective male field sport and from adult data (Table 3, HIR and sprint reference), despite youth participants, a result of limited data in female field sports. Although the specific velocities used in analysis are expected to be different between sports and individualized between athletes, it is important that a standard definition is used to allow interstudy comparisons. However, regardless of these limitations, HIR, sprinting data, and work rate should still be used to inform training especially with consideration of positional and age-specific differences as demonstrated in soccer and rugby union.
It is evident that female performance attributes vary considerably from male counterparts, highlighting the need for more female-specific data. A greater abundance of data combined with more specific determination methods will allow coaches and training staff to develop appropriate practices to enhance competition preparation in female field sports.
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