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The influence of game scheduling on medical encounters at the USA Cup soccer tournament
  1. Nathan G Waibel1,
  2. William O Roberts1,
  3. Scott Lunos2
  1. 1Department of Family Medicine and Community Health, University of Minnesota Medical School, Minneapolis, Minnesota, USA
  2. 2Biostatistical Design and Analysis Center, Clinical and Translational Science Institute, University of Minnesota, Minneapolis, Minnesota, USA
  1. Correspondence to Dr William O Roberts, 1414 Maryland Avenue East, St Paul, MN 55106, USA; rober037{at}umn.edu

Abstract

Objective To investigate the influence of playing multiple games on multiple days on youth soccer medical encounter rates.

Design Prospective cohort survey study.

Setting Medical facility at the 2008 Schwan's USA Cup soccer tournament.

Participants Players presenting to the medical facility for game-related medical evaluation.

Assessment of risk factors Date, game and half of game for each medical encounter.

Main outcome measures Game play-related medical encounters per 1000 match hours (MH).

Results 211 players surveyed with 195 eligible and completed questionnaires. There were 4.06, 5.14 and 3.92 medical encounters/1000 MH on 11, 12 and 13 July, respectively, with no significant difference in injury incidence. There was no difference in medical encounter rates of second games compared with first games of the day (p=0.126). Daily medical encounter rates were 5.65, 8.95, 7.83, 6.94 and 4.62/1000 MH on 15, 16, 17, 18 and 19 July, respectively, with statistically significant differences on 16 July (p<0.001) and 17 July (p=0.022) compared with 15 July. Encounter rates of second games compared with first games of the day showed no difference (p=0.385). A linear test for trend from 15 to 19 July was not significant (p=0.092).

Conclusions The USA Cup format did not show either increased medical encounter rates from the cumulative total of games played or a consistently increased rate in the second game of the day compared with the first. Players, coaches, parents and administrators can feel confident that this tournament format does not pose an additional risk of injury.

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The epidemiology and mechanisms of soccer injuries have been studied on numerous occasions,1,,18 and some are specific to youth soccer.3 6 10 11 13 14 16 18 Several studies focus on specific soccer-related injuries,19,,25 others distinguish between injuries that occurred during game play from those that occurred in practice,1 3 14 and some attempted to break down the game into individual halves or even smaller time periods to look for differences in injury rates.14 26,,30 Most of the articles that discuss injury rates in the first half of the game compared with the second addressed professional soccer tournaments such as the World Cup,26,,29 with a very different scheduling format from the usual youth soccer tournament.

One potential risk factor is the rigor of playing several games within the tight timespan of a youth soccer tournament. There is little known about the effect of playing multiple games on successive days during youth soccer tournaments on the injury rate. There is a need for research into the effect of tournament scheduling on medical encounter rates in youth players to understand the effect of various tournament formats.

This study tested the following hypothesis: there is an increase in medical encounter rates on successive days of the tournament or during the second game of the day compared with the first in this tournament format.

Methods

Study design

This study was a prospective cohort study of participants in two separate tournaments of the 2008 USA Cup (Blaine, Minnesota, USA). The first was the 11–13 July USA Cup Weekend (approximately 450 teams) with round robin play on 11 July and the morning of 12 July and single elimination games starting on the afternoon of 12 July and completed on 13 July. The second was the 15–17 July USA Cup (approximately 500 teams) with round robin play on 15–17 July and single elimination games played on 18 and 19 July. Each team played a minimum of three games in either the USA Cup Weekend or the USA Cup, or six games if entered in both. Players on teams that advanced during the elimination rounds potentially played six games in 3 days in the USA Cup Weekend and seven games in 5 days in the USA Cup. The first games of the day started at 07:50 hours, and the last games started at 19:10 hours. The minimum time interval between games played on the same day was 3 h, except in four games that had just over 1 h recovery time.

Subjects

The tournament included both boys and girls teams from under 13 years to under 19 years brackets. The teams were of varied skill levels in each of the age brackets, and unlimited substitution was allowed in the younger age groups. The games were different lengths based on age, and all were shorter than the age group regulation game length until the final age group championship game (see table 1). Unlimited substitutions were permissible in all games for under 13 years to under 16 years teams and Fédération Internationale de Football Association Substitutions Rules were observed in the under 17 years to under 19 years age groups. When the weather (eg, heat) dictated, the games were further shortened, additional water breaks were instituted and unlimited substitution was allowed for all age groups.

Table 1

USA Cup Weekend and USA Cup game durations

The following inclusion criteria were used to determine medical encounters: participants of either tournament who received medical attention at the central medical facility for injuries sustained or medical issues arising during match play. Medical encounters included: both acute and acute on chronic musculoskeletal injury; skin laceration or abrasion; heat injury, heat exhaustion or heat stroke; and concussion or head injury.

The following exclusion criteria were used: participants injured outside of match play; participants with exercise asthma or asthma, infectious disease, colds, sore throats and medical problems not related to match participation; and non-participants of the tournaments.

All players and a parent/guardian signed a medical liability waiver before entering in the tournament. As a parent/guardian was not always present when an injured participant presented for evaluation, additional consent was waived, and the research team volunteers explained to the participants the study purpose and content, emphasising that participation was voluntary. Each participant was also provided an ‘information sheet’ describing the project and its goals.

Data collection

Any tournament participant who sustained an injury or had a medical issue, and wanted on-site evaluation and treatment, was received at the central medical facility utilising the standard USA Cup tournament medical protocol. More severely injured players were transported directly to the medical facility by the field medical team. Clerical volunteers registered the injured player into the facility and obtained demographic information before evaluation by the medical staff. The data for this study were collected on a separate survey form by the research team volunteers immediately after the participant completed the facility registration, unless the injury severity or urgency required the volunteers to approach the athlete at a later time, and the data collection was independent of the medical care with no bearing on the outcome. No survey data were collected on tournament participants who did not use the central medical facility.

The survey questions were directed at the timing of the injury as it related to the total number of games played during the tournament and the number of games played on the day of injury (figure 1). The survey queried for potential cumulative fatigue by assessing the timing of injury with respect to the first or second half of the game, first or second game of the day, game number of the tournament and the interval between games on the same day and from the previous day. The data were collected on paper forms and entered into a digital database, separate from the medical record. Quality assurance checks conducted on surveys collected early in the tournament detected some missing data, and the data collection process was corrected by retraining the survey administrators. The measured outcome was thetiming of any tournament game related to the medical encounter, in order to assess the effect of multiple games on the medical encounters per 1000 match hours (MH) as a potential indicator of overscheduling. The survey did not collect specific information about the injured players (eg, sex or age) or their injuries (eg, sprain, strain, laceration or fracture). The scope of this study was purposely limited to address the question of playing volume and injury rate and achieve a large enough ‘n’ for the purposes of statistical analysis.

Figure 1

Schwan's USA Cup Survey—2008.

The study was approved by the University of Minnesota Institutional Review Board (0806P36501).

Statistical analysis

The survey data were summarised by means of descriptive statistics using medical encounters per 1000 MH. MH (also known as player game hours) were chosen for the denominator because the total MH for the tournament, each day, and the first and second games, can easily be calculated, and the MH calculation does not require access to the roster and individual game records necessary to assess athlete exposures. For example, a match with 1 h of playing time and 11 players on each side would have 22 MH independent of the roster size and individual player time. Although the playing time of individuals on each team varied, the total playing time and the total MH for each game were constant. Total and daily MH were calculated from the summation of the maximum allowable game time obtained from game schedules for each age level and the maximum number of players allowed on the field. The MH for each game were calculated for each day, the first and second game for each day, and for the tournament to obtain the exposure data. Measuring the incidence per 1000 MH allows a comparison of medical encounter rates as the number of games and players decreased in the elimination arm of each tournament.

Poisson regression was used to model the incidence densities of soccer medical encounters comparing the second game of the day with the first game of the day and comparing sequential days of the tournament with the first day of the tournament. In addition for the USA Cup, the last day of the tournament was compared with the day before. Medical encounters in the second half of game play were compared with the first half for the first and second games of each day. Separate analyses were performed for games on 11–13 and 15—19 July. A linear test of trend from the Poisson regression model was performed to see if there was a day trend. p Values less than 0.05 were considered statistically significant. The GENMOD procedure from SAS version 9.1.3 was used for the analyses.

Results

USA Cup Weekend medical encounter rates

The combined medical encounter rate for the USA Cup Weekend was 4.44/1000 MH and the daily encounter rates are shown in figure 2A. There was no significant between-day difference in the medical encounter incidence for the games (12 July compared with 11 July (p=0.718; incidence density ratio (IDR) 1.26, 95% CI 0.36 to 4.33) or 13 July compared with 11 July (p=0.982; IDR 0.98, 95% CI 0.14 to 6.83)). The daily medical encounter rates for first and second games are shown in figure 3A. There was no significant difference in the medical encounter incidence between the second and first game on any of the tournament days (p=0.126; IDR 0.45, 95% CI 0.16 to 1.25). Medical encounter rates for the second half compared with the first of each game are shown in figure 4A with no significant between-half differences seen for the first (p=0.265; IDR 0.69, 95% CI 0.36 to 1.33) or second (p=0.829; IDR 1.25, 95% CI 0.17 to 9.43) game of the day.

Figure 2

(A) Medical encounters each day/1000 match hours (MH)—USA Cup Weekend. (B) Medical encounters each day/1000 MH—USA Cup.

Figure 3

(A) Medical encounters each game of each day/1000 match hours (MH)—USA Cup Weekend. (B) Medical encounters each game of each day/1000 MH—USA Cup.

Figure 4

(A) Medical encounter game of the day and encounter half—USA Cup weekend. (B) Medical encounter game of the day and encounter half—USA Cup.

USA Cup medical encounter rates

The combined encounter rate for the USA Cup was 6.95/1000  MH and the daily medical encounter rates are also shown in figure 2B. There were statistically significant differences in the medical encounter incidence comparing 16 July with 15 July (p<0.001; IDR 1.58, 95% CI 1.21 to 2.06) and 17 July with 15 July (p=0.022; IDR 1.38, 95% CI 1.05 to 1.82). There was no significant difference seen on either 18 July (p=0.169; IDR 1.21, 95% CI 0.92 to 1.60) or 19 July (p=0.282; IDR 0.82, 95% CI 0.57 to 1.18) compared with 15 July. A linear test for trend from 15 to 19 July was not significant (p=0.092). There was no difference in the medical encounter rates of the second compared with the first games of each day (p=0.385; IDR 0.79, 95% CI 0.47 to 1.34) as shown in figure 3B.

The encounter rate comparisons for the first and second half of each game are illustrated in figure 4B. The second half of the first games played from 15 to 19 July had higher medical encounter rates compared with the first half (p=0.039; IDR 1.62, 95% CI 1.03 to 2.56). No difference was found in the half comparisons of the second game of the day (p=0.766; IDR 1.17, 95% CI 0.42 to 3.22).

In the course of each tournament, 46 players sought medical attention related to the first game, 45 in the second game, 33 in the third game, 40 in the fourth game, 22 in the fifth game and six in the sixth game.

Discussion

The results of this study do not indicate a clear relationship between medical encounter rates and either the total number of games played or the number of games played per day in this tournament. In a previous study of the USA Cup soccer tournaments from 1988 to 1997, the mean injury rate for both boys and girls playing in the tournaments was 13.23 injuries per 1000 MH, and a downward trend in injury rates was noted across the decade, with the lowest injury rate of 8.57/1000  MH in 1996, but the game-to-game and day-to-day injury rates were not addressed.5 The combined girls and boys mean injury rate in the 2008 tournaments was lower than previously identified injury rates. Beyond that, comparison with the previous USA Cup and other tournament studies is difficult as the injury rates are not segregated by game.

The frequency of injuries increased slightly after the first day in both tournaments, but began to trend down in successive days as each tournament progressed to the final day and the number of teams involved in play decreased. There was no significant difference in injury rates between the first and second games of the day in either tournament. This suggests that participation in up to two games a day or in several games in successive days did not increase medical encounter rates, and cumulative fatigue may not be a significant injury risk factor in this tournament format. In the USA Cup, medical encounter rates were significantly increased on the 16 and 17 July compared with 15 July (first day of the tournament), but this difference was not carried through to 18 and 19 July (fourth and fifth days of the tournament). The games on the 15–17 July were in round robin format, in which club teams with lesser skill levels may be paired against select teams that train more vigorously; pitting less evenly matched teams against each other might explain the increase in injury rates. In the single elimination portion of the tournament on 18 and 19 July, opponents were more evenly matched based on performance in the round robin portion of the tournament, which may account for the baseline injury rates.

In the USA Cup Weekend, there was no significant difference between injury rates in the first and second half in either the first or second game of the day. The same was not true for the USA Cup in which there was a greater rate of injury in the second half compared with the first half of the first game, with no significant difference shown in the second game. One potential reason for increased injury in the second half of the game is fatigue, but it would stand to reason that fatigue would be greater in the second game and second game data do not support this explanation. However, players may pace their effort to avoid excessive fatigue, as hypothesised in elite soccer, and play less aggressively in the second game of the day.31 A recent study investigated thermal and cardiovascular strain associated with two identical 80 min bouts of strenuous exercise in the heat separated only by 1 h rest.32 The investigators wanted to see if this group of young athletes could recover adequately with 1 h of rest. The 1 h of cool-down, rest and rehydration was found to be adequate to eliminate the apparent carry-over effects from the first bout of strenuous exercise. Each USA Cup player had 3 h rest between same-day games except for four games that had just over 1 h rest, which should have provided adequate time to recover from the previous game. Most teams in the USA Cup only play one game on each of the first 3 days of the tournament. As the majority of soccer-related injuries occurring in a game are caused by contact,1 3 it is conceivable that these injuries are caused by rough play occurring later in the game.

The data addressing the total games played when an injury occurred were not normalised to MH as a result of insufficient information to calculate the rates; therefore, the effect of cumulative games could look different when normalised, but it is doubtful that the difference would change the conclusions drawn based on the other data presented in this study.

Limitations of the study

MH do not account for injured players who did not finish playing a game or play in subsequent games although the position was likely to be filled by a non-injured team mate. It is possible that some teams played without a full compliment of players on the field as a result of injury or illness. Weather (heat, thunder, lighting and tornadoes) affected the length of some of the games played. These potential factors were not taken into consideration when normalising the data to MH because the change to the denominator data would be minimal and would probably not impact the results.

All injured players may not have reported to the medical area and some participants with a minor injury that did not interrupt play may have chosen to obtain medical treatment at community facilities.

What these data add to this topic

This study evaluates the relationship between games played in a soccer tournament and medical encounter rates. Although this study has limitations, it is a starting point for further investigation into the relationship between the amount of games played in a tournament and resulting injury rates. The results of this study imply that the schedule used in both the USA Cup Weekend and the USA Cup is not a significant risk factor for injury, possibly because the games are shortened from the regulation time, unlimited substitution is allowed for most age groups, and in 2008 the heat stress was not severe.

Suggestions for future studies

Future studies should investigate players who participate in both the USA Cup Weekend and the USA Cup to evaluate the potential fatigue of playing in back-to-back tournaments. It would be useful to know how many players were available to play on the team at the time an injury occurred as a potential gauge of fatigue. Future studies could link the survey to the medical record to include sex, age and type of injury for each injured participant. Tournaments that schedule more than two games on each day, play two games on several consecutive days, use an age-based regulation game duration for all games, or allow play in more severe heat stress conditions need to be studied to identify the threshold at which fatigue becomes an identifiable risk factor for injury.

Conclusions

The USA Cup format of limiting teams to two games per day with decreased game duration until the final game and unlimited substitution of players, did not show either increased medical encounter rates from playing up to two games a day on multiple days or a consistently increased medical encounter rate in the second game of the day compared with the first game. Players, coaches, parents and administrators can feel confident, despite the limitations of this study, that the format of this tournament is not an additional risk factor for injury.

What is already known on this topic

  • Many thousands of youths participate in soccer tournaments, and a percentage of those participants are injured as a result of their participation.

  • Very little is known about the risk of injury a participant takes when entering a multi-day soccer tournament.

What this study adds

  • The formats of the USA Cup Weekend and the USA Cup do not lead to an increased risk of injury.

  • Soccer players, coaches, parents and tournament administrators can feel confident that the format of this tournament is not an additional risk factor for injury.

Acknowledgments

The authors would like to thank the Schwan's USA Cup Medical Director, Steve Elias MD, PhD, for assistance with the implementation of this study, and the numerous volunteers who helped administer the surveys. There was no funding for this study.

References

Footnotes

  • Competing interests None.

  • Patient consent Obtained.

  • Ethics approval The study was approved by the University of Minnesota Institutional Review Board (0806P36501).

  • Provenance and peer review Not commissioned; externally peer reviewed.

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