Risk Factors for Injury in Subelite Rugby League Players

Risk Factors for Injury in Subelite Rugby League Players Tim J. Gabbett,*† BHSc(Hons), PhD, and Nathan Domrow,‡ BSc † From Athlete and Coach Support S...
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Risk Factors for Injury in Subelite Rugby League Players Tim J. Gabbett,*† BHSc(Hons), PhD, and Nathan Domrow,‡ BSc † From Athlete and Coach Support Services, Queensland Academy of Sport, Queensland, ‡ Australia, and the Office of Economic and Statistical Research, Queensland Treasury, Queensland, Australia

Background: Although player fatigue and playing intensity have been suggested to contribute to injuries in rugby league players, no study has confirmed if the level of physical fitness is a risk factor for injury in rugby league players. The aim of this study was to identify risk factors for injury in subelite rugby league players. Hypothesis: Low physical fitness levels are risk factors for injury in subelite rugby league players. Study Design: Cohort study; Level of evidence, 2. Methods: One hundred fifty-three players from a subelite rugby league club underwent preseason measurements of muscular power (vertical jump), speed (10- and 40-m sprint), and maximal aerobic power (multistage fitness test) over 4 competitive seasons. All injuries sustained by players were prospectively recorded over the 4 competitive seasons. Results: The risk of injury was greater in players with low 10- and 40-m speed. Players with a low maximal aerobic power had a greater risk of sustaining a contact injury. In addition, players who completed less than 18 weeks of training before sustaining their initial injuries were at greater risk of sustaining a subsequent injury. Conclusions: Subelite rugby league players with low speed and maximal aerobic power are at an increased risk of injury. In addition, players who complete less than 18 weeks of training before sustaining an initial injury are at greater risk of sustaining a subsequent injury. These findings highlight the importance of speed and endurance training to reduce the incidence of injury in subelite rugby league players. Keywords: rugby league; odds ratio; prevention; subelite; physical characteristics

such as running, passing, and sprinting, separated by short bouts of low-intensity activity such as walking and jogging.18 During the course of a match, players are exposed to numerous physical collisions and tackles.2 As a result, musculoskeletal injuries are common.6 Several studies have documented the incidence, site, nature, and cause of injuries in rugby league.8,15 Depending on the level of competition, the incidence of injury in rugby league has been reported to be in the range of 26.8 to 67.7 per 1000 playing hours,7,13-15 with the majority of injuries occurring in tackles.7,13 Although these studies have provided important information on the extent of the injury problem in rugby league and the cause of these injuries, the implementation and evaluation of effective injury prevention strategies are also dependent on the identification of injury risk factors.25 To date, no study has investigated risk factors for injury in rugby league players. Poor player fitness levels and low training frequency have been reported to be risk factors for injury in rugby union players.16,21,24 However, although player fatigue8 and playing intensity7,14 have been suggested to contribute to rugby league injuries, no study has confirmed if low phys-

Rugby league is a collision sport played throughout several countries worldwide, including Australia, New Zealand, France, Russia, Wales, Scotland, Ireland, Papua New Guinea, Fiji, Samoa, and South Africa.2 The sport has similar rules and movement patterns to rugby union; however, unlike rugby union, rugby league does not have a line-out, involves 13 players per team (rather than 15), and involves an immediate play-the-ball after each tackle.2 In Australia, approximately 171 000 adults and children play rugby league,1 with the majority of these participants competing at the subelite level. The game is physically demanding, requiring players to compete in a challenging contest involving frequent bouts of high-intensity activity

*Address correspondence to Dr Tim J. Gabbett, BHSc(Hons), PhD, Queensland Academy of Sport, PO Box 956, Sunnybank, Queensland 4109, Australia (e-mail: [email protected]). No potential conflict of interest declared. The American Journal of Sports Medicine, Vol. 33, No. 3 DOI: 10.1177/0363546504268407 © 2005 American Orthopaedic Society for Sports Medicine

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ical fitness is a risk factor for injury in rugby league players. In addition, although previous injury has been identified as a risk factor for subsequent injury in other collision sports,16,20,21 the influence of previous injury on subsequent injury in rugby league is unknown. Therefore, the purpose of this study was to identify risk factors for injury in subelite rugby league players.

MATERIALS AND METHODS One hundred fifty-three rugby league players participated in this 4-year prospective study (2000-2003). Of the 153 players, 84 players (54.9%) played 1 season, 51 players (33.3%) played 2 seasons, 14 players (9.2%) played 3 seasons, and 4 players (2.6%) played all 4 seasons. The number of players participating in each season was 66, 66, 47, and 65, respectively, giving a total of 244 player-seasons. All players were registered with the same subelite rugby league club and were competing in the Gold Coast Group 18 (New South Wales Country Rugby League, Australia, 2000-2002) or South-East Queensland (Queensland Rugby League, Australia, 2003) senior rugby league competition. In rugby league in Australia, there are several different playing levels, which can be generally classified as elite (fully paid professional players), subelite (receive moderate remuneration to play rugby league but also rely on additional employment to generate income), and nonelite (fully amateur players). The players in the present study were defined as subelite, as they were receiving moderate remuneration to play rugby league but were also relying on additional employment to generate income.13 All subjects received a clear explanation of the study, including the risks and benefits of participation, and written consent was obtained. The Institutional Review Board for Human Investigation approved all experimental procedures.

Fitness Testing Battery Each season lasted from December through September, with matches played from January through September. All players underwent fitness testing in December as part of their preseason training program. Players who played more than one season had their fitness reassessed at the beginning of each subsequent preseason preparation period. Muscular power (vertical jump),4 speed (10- and 40-m sprint),11 and maximal aerobic power (multistage fitness test)22 were the fitness tests selected. The age, playing experience, and body mass of players were also documented. Players were instructed to refrain from strenuous exercise for at least 48 hours before the fitness testing session and to consume their normal pretraining diets before the testing session. At the beginning of the fitness testing session, body mass was recorded for all players using calibrated analog scales (Seca, Hamburg, Germany). Scales were calibrated using a 3-point calibration of 20-, 60-, and 100-kg weights. After measurement of body mass, players underwent a standardized warm-up (progressing from low to higher intensity activity) and stretching routine. Fluid

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intake was permitted ad libitum after the measurement of body mass. Players performed 2 trials for the speed (10and 40-m sprint) and muscular power (vertical jump) tests, with a recovery of approximately 3 minutes between trials. Players were encouraged to perform low-intensity activities and stretches between trials. The field testing session was concluded with players performing the multistage fitness test (estimated maximal aerobic power). Muscular Power. Lower body muscular power was evaluated by means of the vertical jump test4 using the Yardstick vertical jump device (Swift Performance Equipment, New South Wales, Australia). Players were requested to stand with feet flat on the ground, extending their arms and hands, and the standing reach height was marked. After assuming a crouch position, each subject was instructed to spring upward and touch the Yardstick device at the highest possible point. No specific instructions were given regarding the depth or speed of the countermovement.4 Vertical jump height was calculated as the distance from the highest point reached during standing and the highest point reached during the vertical jump. Vertical jump height was measured to the nearest 1 cm, with the highest value obtained from 2 trials used as the vertical jump score. The intraclass correlation coefficient for test-retest reliability and typical error of measurement for the vertical jump test were 0.96 and 3.3%, respectively. Speed. The running speed of players was evaluated with a 10- and 40-m sprint effort11 using electronic timing gates (Speed Light Model TB4, serial No. 4921001, Southern Cross University Technical Services, Lismore, Australia). The timing gates were positioned 10 and 40 m cross-wind from a predetermined starting point. Players sprinted from a standing start.11 Players were instructed to run as quickly as possible along the 40-m distance. Speed was measured to the nearest 0.01 second, with the fastest value obtained from 2 trials used as the speed score. For the 10- and 40-m sprint tests, the intraclass correlation coefficients for test-retest reliability were 0.95 and 0.97, respectively, and the typical errors of measurement were 1.8% and 1.2%, respectively. Maximal Aerobic Power. Maximal aerobic power was estimated using the multistage fitness test.22 Players were required to run back and forth (ie, shuttle run) along a 20-m track, keeping in time with a series of signals on an audiocassette. The frequency of the audible signals (and, hence, running speed) was progressively increased, until subjects reached volitional exhaustion. The multistage fitness test tape was calibrated before each test in accordance with procedures outlined by Ramsbottom et al.22 Maximal aer. obic power (VO2max) was estimated using regression equations described by Ramsbottom et al.22 When compared to . treadmill-determined VO2max, it has been demonstrated that the multistage fitness test provides a valid estimate of maximal aerobic power.22 In addition, all players completed duplicate multistage fitness tests, performed 1 week apart, before the commencement of this study. The intraclass correlation coefficient for test-retest reliability and typical error of measurement for the multistage fitness test were 0.90 and 3.1%, respectively.

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TABLE 2 Site, Nature, and Cause of Injuries Sustained Over 4 Competitive Playing Seasonsa

TABLE 1 Potential Risk Factors for Injury in Subelite Rugby League Players Physical, Physiological, and Training Factors

Rugby League–Specific Factors Rate

Age Body mass 10-m speed 40-m speed Muscular power VO2max Training weeks to injury

.

Playing experience Playing position Playing level Matches to injury Injury exposure Cause of injury Severity of injury Proportion of season missed

Definition of Injury Players participated in 1 match per week. All injuries sustained to the total cohort of 153 players were prospectively recorded over the 4 competitive seasons. Injury data were collected from 219 matches, which included all trial, fixture, and finals matches. For the purpose of this study, an injury was defined as any pain, disability, or injury that occurred as a result of a competition match that caused the player to miss a subsequent match.14 The number of matches missed as a result of the injury was also recorded. Injuries were classified as minor (1 match missed), moderate (2-4 matches missed), and major (5 or more matches missed).14

Statistical Analysis Statistical analysis was performed in SAS using the PROC GENMOD procedure (SAS Institute, Cary, NC). The statistical model was fitted in PROC GENMOD using generalized estimating equations27 and incorporating repeatedmeasures analysis. An autoregressive correlation structure was assumed to measure temporal effects of the observations. As the dependent variable was dichotomous, both categorical and continuous variables were collapsed and grouped to ensure that approximately a third of observations fell within each level. A list of these categories can be seen in Table 1. Odds ratios (ORs) were calculated to determine which factors increased or decreased the risk of injury, with 1 of the levels chosen as the reference level. A value greater or less than 1 implied an increased or decreased risk of injury, respectively. Also, 95% confidence intervals (CIs) for the ORs were calculated. Where the confidence interval did not contain the null value (OR = 1.0), the OR was taken as being significant at the P < .05 level.

RESULTS A total of 219 matches were played over the 4 seasons. The total exposure time was 3341 playing hours. Of the 153 players, 94 players (61.4%) recorded 1 or more injury in 1

Site of injury Thigh/calf Shoulder Knee Ankle/foot Head/neck Thorax/abdomen Arm/hand Face Other Nature of injury Joint sprains Muscle strains Fractures/dislocations Hematomas Concussions Contusions Lacerations Abrasions Other Cause of injury Being tackled While tackling Fall/stumble Overexertion Struck by player Collision with player/object Overuse Twisting to pass/accelerate Other

95% Confidence Interval

11.7 10.2 8.4 6.6 5.7 4.5 4.5 1.2 2.7

8.0-15.3 6.8-13.6 5.3-11.5 3.8-9.4 3.1-8.3 2.2-6.8 2.2-6.8 0.0-2.4 0.9-4.5

19.2 11.1 7.5 6.0 3.0 2.7 1.5 0.3 3.3

14.5-23.8 7.5-14.7 4.6-10.4 3.4-8.6 1.1-4.9 0.9-4.5 0.2-2.8 0.0-0.9 1.4-5.2

16.5 13.2 5.4 3.9 3.6 3.3 1.2 0.9 7.5

12.1-20.9 9.3-17.1 2.9-7.9 1.8-6.0 1.6-5.6 1.4-5.2 0.0-2.4 0.0-1.9 4.6-10.4

a

Values are reported as rates per 1000 playing hours.

or more seasons (185 injuries in total). When expressed relative to exposure hours, the incidence of injury was 55.4 (95% CI, 47.4-63.4) per 1000 playing hours. The most common site of injury was the thigh and calf (11.7 [95% CI, 8.0-15.3] per 1000; 21.1%), whereas injuries to the shoulder (10.2 [6.8-13.6] per 1000; 18.4%) and knee (8.4 [5.311.5] per 1000; 15.1%) were less common. Joint sprains (19.2 [14.5-23.8] per 1000; 34.6%) were the most common type of injury, whereas muscle strains (11.1 [7.5-14.7] per 1000; 20.0%) and fractures and dislocations (7.5 [4.6-10.4] per 1000; 13.5%) were less common. Injuries were most commonly sustained while being tackled (16.5 [12.1-20.9] per 1000; 29.7%) and while tackling (13.2 [9.3-17.1] per 1000; 23.8%) (Table 2). The most common specific injuries were lateral ankle sprains (6.9 [4.1-9.7] per 1000; 12.4%), acromioclavicular joint injuries (4.5 [2.2-6.8] per 1000; 8.1%), and knee medial ligament sprains (3.9 [1.8-6.0] per 1000; 7.0%) (Table 3). Variables included in the initial multivariate analysis for all injuries were body mass, age, playing experience, grade, position, 10- and 40-m speed, muscular power, and

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TABLE 4 Risk Factors for Injury, Controlling for Other Risk Factors in the Model

TABLE 3 Incidence of Common Specific Injuriesa

Specific Injury

Rate

95% Confidence Interval

6.9 4.5 3.9 3.0 2.7 2.1 2.1 1.8 1.8 1.8 1.8 1.5 1.5 1.5 1.2 1.2 1.2 0.9 0.9 0.6 0.6 0.6 0.6 0.6 0.6 0.3 0.3 0.3 0.3

4.1-9.7 2.2-6.8 1.8-6.0 1.1-4.9 0.9-4.5 0.5-3.7 0.5-3.7 0.4-3.2 0.4-3.2 0.4-3.2 0.4-3.2 0.2-2.8 0.2-2.8 0.0-2.8 0.0-2.4 0.0-2.4 0.0-2.4 0.0-1.9 0.0-1.9 0.0-1.4 0.0-1.4 0.0-1.4 0.0-1.4 0.0-1.4 0.0-1.4 0.0-0.9 0.0-0.9 0.0-0.9 0.0-0.9

Body mass, kg Less than 81 81-92 93 or more (reference) Age group, y 18 and younger 19-22 23 or older (reference) Playing experience, y Less than 10 10-15 16 or more (reference) 10-m speed, s Less than 1.98 1.98 to less than 2.20 2.20 or more (reference) 40-m speed, s Less than 5.76 5.76 to less than 6.10 6.10 or more (reference) Muscular power, cm Less than 42.5 42.5 to less than 52.0 52.0 or more (reference) VO2max, mL kg–1 min–1 Less than 42.8 42.8 to less than 47.7 47.7 or more (reference)

.

95% Confidence Interval

P

0.51 0.23 1

0.16-1.58 0.06-0.93

.242 .040

1.97 0.82 1

0.44-8.84 0.21-3.3

.377 .782

0.10 0.15 1

0.02-0.48 0.04-0.65

.004 .011

2.59 10.28 1

0.19-35.24 1.40-75.67

.476 .022

6.72 9.93 1

0.64-71.07 1.30-75.62

.113 .027

2.37 0.69 1

0.55-10.28 0.17-2.78

.249 .597

0.59 0.35 1

0.21-1.68 0.11-1.14

.323 .082

Odds Ratio

Factor Ankle sprain (lateral) Acromioclavicular joint injuries Knee medial ligament sprain/tear Concussion Quadriceps hematoma ACL sprain/tear Rotator cuff abnormality Calf hematoma Calf strain Hamstring strain Neck strain Dislocated shoulder Low back strain Fractured metacarpal Knee lateral ligament sprain/tear Rib fracture/bruising Sternum fracture/bruising Facial laceration Groin strain Achilles tendinitis Calf contusion Fractured clavicle Head laceration Shoulder joint strain Fractured tibia/fibula Clavicle contusion Dislocated finger Dislocated knee Facial fracture

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.

.

a

Values are reported as rates per 1000 playing hours.

.

estimated VO2max. Although age, muscular power, and, to a lesser extent, maximal aerobic power were not significant factors in the cause of injury, they did have an underlying effect on some variables and were subsequently left in the model. The justification for including nonsignificant terms in a model is discussed by McCullagh and Nelder.17 The risk factors for all injuries are shown in Table 4. The risk of injury was significantly greater (P < .05) in players with low 10-m (OR = 10.28 [95% CI, 1.40-75.67]) and 40-m (OR = 9.93 [1.30-75.62]) speed. The risk of injury was significantly lower (P < .05) in heavier players (OR = 0.23 [0.06-0.93]) and in those with less than 15 years of playing experience (OR = 0.15 [0.04-0.65]). The risk factors for contact injuries are shown in Table 5. Variables included in the initial multivariate analysis were body mass, age, playing experience, grade, position, . 10- and 40-m speed, muscular power, estimated VO2max, matches played, training weeks to injury, and injury exposure. Forwards (OR = 4.27. [95% CI, 1.28-14.29]) and players with a low estimated VO2max (OR = 6.20 [1.23-31.15]) had a significantly higher (P < .05) risk of sustaining contact injuries than the reference group. The risk of sustain-

ing contact injuries was significantly lower (P < .05) in second-grade players (OR = 0.13 [0.02-0.86]). The risk factors for the severity of injury are shown in Table 6. Variables included in this analysis were body mass, age, playing experience, grade, position, 10- and 40. m speed, muscular power, estimated VO2max, matches played, training weeks to injury, injury exposure, and whether the injury was a contact or noncontact injury. Players with low body mass had a higher (P < .05) risk of sustaining severe injuries (OR = 2.99 [95% CI, 1.05-8.54]) than the reference group. The risk of severe injury was significantly lower (P < .05) in players with less than 10 years of playing experience (OR = 0.22 [0.07-0.77]). The risk factors for multiple injuries are shown in Table 7. Variables included in this analysis were body mass, age, playing experience, grade, position, 10- and 40-m speed, . muscular power, estimated VO2max, matches played, training weeks to injury, injury exposure, severity of initial injury, whether the initial injury was to the upper or lower body, and whether the initial injury was a contact or noncontact injury. Players who sustained an initial injury that resulted in 2 to 4 missed matches were at increased risk

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TABLE 5 Risk Factors for Contact Injury, Controlling for Other Risk Factors in the Model

Grade First Second Under 19 (reference) Playing position Forward Back (reference) VO2max, mL kg–1 min–1 Less than 42.8 42.8 to less than 47.7 47.7 or more (reference)

.

95% Confidence Interval

P

0.35 0.13 1

0.06-2.21 0.02-0.86

.266 .034

4.27 1

1.28-14.29

.018

6.20 1.45 1

1.23-31.15 0.41-5.17

.027 .564

Odds Ratio

Factor

.

.

TABLE 7 Risk Factors for Multiple Injuries, Controlling for Other Risk Factors in the Model

TABLE 6 Risk Factors for Severe Injury, Controlling for Other Risk Factors in the Model

Factor Playing experience, y Less than 10 10-15 16 or more (reference) Body mass, kg Less than 81 81-92 93 or more (reference)

Odds Ratio

95% Confidence Interval

Factor Training to first injury, wk Less than 18 18-24 25 or more (reference) Grade First Second Under 19 (reference) Severity of first injury Major Moderate Minor (reference)

95% Confidence Interval

P

8.69 4.49 1

1.33-56.76 0.71-28.6

.024 .111

0.17 0.09 1

0.02-1.22 0.01-0.75

.079 .025

0.18 5.83 1

0.02-1.51 1.09-31.04

.114 .039

Odds Ratio

TABLE 8 Risk Factors for Lower Body Injury, Controlling for Other Risk Factors in the Model P Factor

0.22 0.85 1

0.07-0.77 0.27-2.66

.017 .781

2.99 0.75 1

1.05-8.54 0.25-2.26

.041 .609

(OR = 5.83 [95% CI, 1.09-31.04], P < .05) of sustaining a subsequent injury. In addition, players who completed less than 18 weeks of training before sustaining the initial injury were at greater risk (OR = 8.69 [1.33-56.76], P < .05) of sustaining a subsequent injury than players who completed 25 weeks or more of training. The risk of secondgrade players sustaining multiple injuries was low (OR = 0.09 [0.01-0.75], P > .05). The risk factors for sustaining a lower body injury are shown in Table 8. Variables included in this analysis were body mass, age, playing experience, grade, position, . 10and 40-m speed, muscular power, estimated VO2max, matches played, training weeks to injury, injury exposure, severity of initial injury, and whether the initial injury was a contact or noncontact injury. Heavier players had a greater risk (OR = 6.39 [95% CI, 1.71-23.87], P < .05) of sustaining lower limb injuries. In addition, the risk of sustaining a lower limb injury was greater (P < .05) if the injury was sustained as a result of direct contact (OR = 43.00 [4.34-426.56]).

Body mass, kg Less than 81 81-92 93 or more (reference) Cause of injury Contact Noncontact (reference)

Odds Ratio

95% Confidence Interval

P

0.60 6.39 1

0.19-1.90 1.71-23.87

.385 .006

43.00 1

4.34-426.56

.001

DISCUSSION The present study is the first to investigate risk factors for injury in rugby league players. The results of this study demonstrated that subelite rugby league players with low speed and maximal aerobic power are at an increased risk of injury. In addition, players who completed less than 18 weeks of training before sustaining an initial injury were at greater risk of sustaining a subsequent injury. These findings provide some explanation for the high incidence of fatigue-related injuries in rugby league players.8 In addition, these findings highlight the importance of speed and endurance training to enhance performance and reduce the incidence of injury in subelite rugby league players. The finding of a higher risk of contact injuries in forwards is to be expected given that forwards spend a significant proportion of match play involved in tackling and physical collisions.18 In addition, the finding of lower injury risk in second-grade players is consistent with pre-

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vious injury studies that have shown that the incidence of injury is lower at lower playing levels.6,9 The major . new finding of this study was that a low estimated VO2max increased the risk of contact injuries. Although timemotion studies have shown that the majority of match play is spent in low-intensity activities,18 the intensity of rugby league matches is increased through the large number of physical confrontations and tackles.2 Therefore, the finding of .a higher risk of contact injuries in players with a lower VO2max may be expected. It is likely that because . these players have a lower VO2max, any absolute workload placed on them during a match would pose a higher relative physiological strain on these players.5 As a result, recovery between high-intensity bouts of activity would be reduced, thereby hastening the onset of fatigue. These findings may provide some explanation for the high incidence of fatigue-related injuries in rugby league players.8 Furthermore, players who completed less than 18 weeks of training before sustaining the initial injury were at greater risk of sustaining a subsequent injury than players who completed 25 weeks or more of training. Collectively, these findings highlight the importance of endurance training to enhance performance and reduce the incidence of injury in subelite rugby league players. Given that the majority of rugby league injuries occur in tackles,7,13 and in the second half of matches,8 injury prevention strategies and physical fitness training could include game-specific attacking and defensive drills practiced under fatigued conditions to encourage players to make appropriate decisions and apply learned skills during the pressure and fatigue of competitive matches.13 The finding that players who completed less training were at greater risk of sustaining a subsequent injury is in agreement with some24 but not all16 studies of collision sport athletes. Upton et al24 reported that a lack of preseason training increased the risk of injury in schoolboy rugby union players. However, Lee et al16 found a greater risk of injury in rugby union players who attended training more frequently. The higher injury risk in the rugby union players who attended training more frequently may be because of residual fatigue associated with heavy preseason training or an increased playing intensity accomplished through increased fitness levels.16 Although the present study found that players who completed less training were at greater risk of sustaining a subsequent injury, increasing training loads and fitness levels may not reduce the incidence of injury.12 Indeed, although improving player fitness may reduce the incidence of fatigue-related injuries, it is possible that a greater work capacity could increase playing intensity and, as a result, increase the incidence of injury in subelite rugby league players.13 The present study found that players with low 10- and 40-m speed had an increased risk of injury. In addition, players with lower body mass had a greater risk of injury and injury severity. It has recently been shown that the speed of matches may influence injury rates in collision sports, with greater playing intensity and match speeds resulting in higher injury rates.19 The finding of greater injury risk in slower, lighter players may reflect their

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reduced ability to generate and tolerate high-impact forces associated with tackles.10 Certainly, a heavier player moving at high speed toward the defensive line would have a greater performance advantage and reduced injury risk than a slower, lighter player. In addition, the greater injury risk in players with lower speed may reflect a reduced ability of the players to position themselves correctly before effecting the tackle. In the present study, players who sustained a moderately severe injury were at increased risk of sustaining a subsequent injury. These findings are in agreement with other studies of collision sports that have found a significant relationship between an initial injury event and subsequent injuries.3,26 Another interesting finding from the present study was the reduced risk of injury and injury severity in players with less than 10 to 15 years of playing experience. Playing experience23 and previous injury20 have been shown to be risk factors for subsequent sporting injury. It is likely that players with greater playing experience (more than 16 years of experience) had also sustained more injuries throughout their playing careers than inexperienced players (ie, less than 15 years of experience). The lower risk of injury in inexperienced players may be because of fewer previous injuries sustained while participating in rugby league. In summary, the present study is the first to investigate risk factors for injury in rugby league players. The results of this study demonstrated that subelite rugby league players with low speed and maximal aerobic power are at an increased risk of injury. In addition, players who completed less than 18 weeks of training before sustaining an initial injury were at greater risk of sustaining a subsequent injury. These findings provide some explanation for the high incidence of fatigue-related injuries in rugby league players.8 In addition, these findings highlight the importance of speed and endurance training to enhance performance and reduce the incidence of injury in subelite rugby league players. REFERENCES 1. Australian Bureau of Statistics. Participation in Sport and Physical Activities, Australia. Canberra: Australian Bureau of Statistics; 2000. 2. Brewer J, Davis J. Applied physiology of rugby league. Sports Med. 1995;20:129-135. 3. Dryden DM, Francescutti LH, Rowe BH, Spence JC, Voaklander DC. Personal risk factors associated with injury among female recreational ice hockey players. J Sci Med Sport. 2000;3:140-149. 4. Ellis L, Gastin P, Lawrence S, et al. Protocols for the physiological assessment of team sport players. In: Gore CJ, ed. Physiological Tests for Elite Athletes. Champaign, Ill: Human Kinetics; 2000:128144. 5. Gabbett TJ. Incidence of injury in amateur rugby league sevens. Br J Sports Med. 2002;36:23-26. 6. Gabbett TJ. Incidence of injury in junior and senior rugby league players. Sports Med. In press. 7. Gabbett TJ. Incidence of injury in semi-professional rugby league players. Br J Sports Med. 2003;37:36-43. 8. Gabbett TJ. Incidence, site, and nature of injuries in amateur rugby league over three consecutive seasons. Br J Sports Med. 2000;34:98-103.

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