Knee Surg Sports Traumatol Arthrosc (2015) 23:899–905 DOI 10.1007/s00167-014-3411-9
SPORTS MEDICINE
Sports injury prevention in Swedish elite floorball players: evaluation of two consecutive floorball seasons Ulrika Tranaeus · Urban Johnson · Andreas Ivarsson · Björn Engström · Eva Skillgate · Suzanne Werner
Received: 8 August 2014 / Accepted: 27 October 2014 / Published online: 2 November 2014 © European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA) 2014
Abstract Purpose The objective was to evaluate the effect of a psychological group-based injury prevention, which was implemented throughout the first season, after the second season, in Swedish elite floorball teams (males and females). The secondary objective was to evaluate the effect of the intervention over the two consecutive floorball seasons as a whole. Methods Twenty-three teams in the premier leagues for males and females volunteered and were allocated to an intervention group, n = 175 players, and a control group n = 171 players. The intervention group participated in psychological skills training during the first season. The control group did not receive any alternative treatment. Neither of the groups received any intervention during the second season. All injuries were registered and documented
U. Tranaeus · U. Johnson · A. Ivarsson Center of Research on Welfare, Health and Sport, Halmstad University, Halmstad, Sweden U. Tranaeus · B. Engström · S. Werner Department of Molecular Medicine and Surgery, Stockholm Sports Trauma Research Center, Karolinska Institutet, Stockholm, Sweden U. Tranaeus (*) · B. Engström · S. Werner Capio Artro Clinic, Sophiahemmet, Box 5605, 114 86 Stockholm, Sweden e-mail: [email protected] E. Skillgate Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden E. Skillgate Scandinavian College of Naprapathic Manual Medicine, Stockholm, Sweden
according to time-loss definition and classified into either traumatic or overuse injuries. Results Ninety-three players (27 %) sustained 119 injuries during the second season. The intervention group 0.31 (95 % CI 0.22–0.39) and the control group 0.41 (95 % CI 0.29–0.53) injuries/player. The injury incidence decreased in the intervention group and was lower than the control group. The analysis showed no statistical differences when comparing the intervention group and the control group neither after the second season nor after the two seasons together, Cohen’s d 0.2. Conclusion This group-based training showed a small effect size after the second year resulting in fewer injuries, especially severe injuries, in the intervention group compared to the control group. It is, therefore, important not to overlook the potential of a group-based psychological injury prevention programme. Level of incidence II. Keywords Athletic injury · Behaviour · Overuse injury · Psycho-education · Traumatic injury
Introduction The high incidence of injuries in sports is well documented, [2, 3, 19] showing a need for prevention of sports injuries [17, 31]. Previous studies on injury prevention suggest the use of research frameworks [4, 40] approached from different angles, for instance, implementation issues [11] and behavioural matters [41]. Most prevention research evaluates the effect of the intervention immediately after or close to the completion of the intervention. Successful injury prevention should work in the long-term perspective. Subsequently, this requires an evaluation after longer period of
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time. Therefore, in the present study, evaluation of the first season’s intervention of psychological skills training [39] has been performed at the end of the second consecutive season. Documentation of psychological factors as predictors for sport injuries has been reported in previous research [20, 22]. This is in line with theoretical models suggesting that some psychosocial and historical variables may be risk factors for injuries [1, 42]. These risk factors may be present along with many other intrinsic factors (e.g. age, gender, skill level [1]). Stress has also been reported to be a source of injuries [6, 15, 29]. Stress levels are discussed as being influenced by one’s history of stress, personality factors that predispose people to have substantial stress responses, and coping recourses [42]. Accordingly, studies on injury prevention aimed to reduce perceived stress levels, as well as stress reactions, have been conducted [23]. Three studies [25, 30, 34] used relatively long time frames for an evaluation after the end of an intervention (12 weeks or a completed sport season), whereas three other studies evaluated the intervention immediately after the intervention was finished [7, 21, 24]. These studies further showed the potential effect of using psychological interventions to prevent sport injuries and reduce the time-loss from sport due to injury. None of these studies, however, consisted of large cohorts. To our knowledge, only a few intervention studies have evaluated preventive effects after a longer period of time (e.g. a second season or more) [26, 27], and none of these studies evaluated a psychological intervention focusing on injury incidence in consecutive seasons. Floorball is an indoor team sport with a growing number of players worldwide. The rules and game format are the same for both male and female teams. Three previous studies on floorball reported seasonal incidences of 0.34 injuries/player in males and females [37], 0.46 injuries/player in females [32], and 0.49 injuries/player in males and females [39], respectively. Two injury prevention studies have previously been performed in high-level floorball players [33, 39]. Neuromuscular leg training for female floorball players reduced the injury risk to the lower
extremity by 66 % in an intervention group (n = 256) compared to a control group (n = 201) [33]. A psychological skills training programme including male and female floorball players did not result in significant differences between an intervention group (n = 193) and a control group (n = 208) at the end of the season [39]. Injury prevention strategies are implemented to influence a behavioural change with a long-term goal to reduce as many injuries, in as many athletes, as possible [11]. The hypothesis is that a psychological skills training programme might reduce the number of injuries after a consecutive season. Therefore, it is of clinical relevance to evaluate such an intervention over a longer period, e.g. the consecutive season, and injuries as one unit and to separate traumatic and overuse injuries due to their different injury mechanisms [1, 40]. To our knowledge, no second-season follow-up study of a psychological group intervention has been published earlier. The primary objective with the present study was to evaluate injury prevention of a psychological skills training group-based intervention programme, the season after the implementation (i.e. at the end of the second season in elite floorball teams for males and females). The secondary objective was to evaluate the effect of the intervention over the two consecutive floorball seasons as a whole.
Materials and methods This prospective study was carried out during the seasons 2010/2011 and 2011/2012 in the Swedish Floorball Federation’s elite leagues. The leagues consist of 28 teams, 14 male teams and 14 female teams. Twenty-three teams, 11 male teams and 12 female teams, totalling 346 players (174 males and 172 females), volunteered to participate in the study during the two seasons with completed injury records (Table 1). These players fulfilled the inclusion criteria, which were to understand the Swedish language; to be able to respond on psychometric instruments and questionnaires; and, for the intervention group, to participate in
Table 1 Gender-specific characteristics of the study participants Intervention group (n = 175)
Control group (n = 171)
Age Floorball experiencea Injured players, Season 1b
Male (n = 87) 23.9 ± 3.9 14.4 ± 3.4 34 (39 %)
Female (n = 88) 22.0 ± 4.9 12.3 ± 3.1 33 (37 %)
Male (n = 87) 24.9 ± 4.5 13.7 ± 4.6 40 (46 %)
Female (n = 84) 22.8 ± 4.4 11.9 ± 3.2 35 (42 %)
Exposure hours to floorball per weekc
6.1 ± 0.6
6.1 ± 1.0
6.2 ± 0.9
6.7 ± 0.7
Gender a
a
Mean years and standard deviation
b
Season 2010/2011
c
Mean hours/week and standard deviation during game season
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a provided psychological intervention programme. During the study, 55 players (13 %) dropped out. This was because they stopped playing floorball (n = 27) or they belonged to teams that did not report the injuries during the second season [e.g. transferred to teams abroad or to teams in Sweden with no or new medical staff (n = 28)]. The analysis of the dropouts showed no significant differences in age, floorball experience, previous injuries, or exposure to floorball (Table 2). The cohort was closed, meaning that new players coming into any of the teams were not included in the analysis. Procedure The Swedish Floorball Federation gave the approval to conduct this study. In springtime 2010, the coaches gave their approval to their teams’ participation and the athletes made the final decision to participate. The athletes received verbal and written information regarding the study and its purpose. Those athletes that participated gave their written consent to participate, contact information, baseline information, and completed psychometric instruments (reported elsewhere). The teams’ medical staffs were asked to document injuries starting from preseason training and continuously onwards through the two seasons. The hours of exposure were calculated from time periods involved in compulsory floorball training and games during preseason and competitive season. The teams were consecutively allocated to an intervention group n = 11 (males n = 94, females n = 99) or a control group n = 12 (males n = 109, females n = 99) by the first author [26]. At the same time as the teams reported that they accepted to participate in the study, they were asked to participate in the intervention group. This procedure continued until eleven teams were included. The players in the intervention group took part in a psychological skills training programme starting in the fall of the first study season, 2010/2011, whereas Table 2 Characteristics of the players that participated and those players that dropped out in-between the two seasons Players (n = 346)
Dropouts (n = 55)
p value Effect size
Agea
22.4 ± 4.2 Injuries presea- 0 (0–2) son (n) 1b
22.8 ± 4.9 0 (0–2)
n.s n.s
0.001c 0.18d
Injuries season 0 (0–6) (n) 1b
0 (0–3)
n.s
0.16d
Years in floorball (n)a
11.4 ± 4.9
n.s
0.003c
12.2 ± 3.5
n = number a Mean and standard deviation, and d Cohen’s d
b
median (range), effect size: c eta2
the players in the control group did not receive this or any other intervention. The psychological skills training programme was conducted by external sport psychology consultants. During the second preseason and full-game season, 2011/2012, all teams, irrespective of group membership, were prospectively followed without any intervention. The medical staff for each team continued to record injuries throughout the second season. Injury surveillance Injuries were defined as time-loss events with the following categories: mild (1–7 days absence from regular training or games), moderate (8–30 days absence from regular training and games), and severe (absence from floorball for more than 30 days) [43]. Injuries were also classified into traumatic injuries and overuse injuries [13]. The teams were offered the use of the Swedish National Injury Register. This web-based on-line registration was customised to fit the present study and was provided to all teams by the Swedish Floorball Federation. Intervention Sessions covering somatic and cognitive contents: e.g. relaxation, stress management, control of emotions, and goal setting were used to equip the teams with strategies to reduce the stress response (according to Williams and Andersen’s stress injury model) [42]. The intervention was developed to educate the entire team (players and staff) at the same time and was provided by sport psychology consultants. Appointments for sessions were scheduled to fit the team. The interventions were tailored for elite floorball and consisted of six meetings developed to last approximately 1 h each; details are presented elsewhere [39]. The present study was approved by the Regional ethical board, Karolinska Institutet, Stockholm, Sweden, Dnr 2009/2001-31. Statistical analysis An a priori sample size calculation was preformed to find out the number of participants needed to reach a power of 0.8. For this calculation, alpha was set to 0.05. Furthermore, the sample size was based on both the results of earlier studies [21, 25, 39] and the context. The estimated Cohen’s d effect size was 0.5 (a moderate effect size). Including these statistics into a power analysis results showed in an estimate that a minimum of 64 participants, in each group, were needed to reach sufficient power (β = 0.8). The data were analysed using IBM, SPSS version 20 to investigate injury incidence, differences in injury rates (injuries/1,000 exposure hours), and kinds of injuries between the
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Table 3 The injury frequency and proportions (percentage of total) Intervention Male (n = 87)
Control Female (n = 88)
Trauma Overuse Trauma Overuse Mild Moderate Severe
4 10 4
3 1 3
Total n (%) 18 (15) 7 (6)
9 4 2
7 4 0
15 (12) 11 (9)
Total
Total (n = 175)
Male (n = 87)
23 (19) 19 (16) 9 (8)
6 6 8
51 (43)
20 (17) 11 (9)
Female (n = 84)
Trauma Overuse Trauma Overuse 6 2 3
15 2 3
14 0 3
20 (17) 17 (15)
Total (n = 171)
All (n = 346) Trauma n (%)
Overuse n (%)
41 (34) 10 (8) 17 (14)
34 (29) 22 (18) 17 (14)
30 (25) 7 (6) 9 (8)
68 (57)
73 (61)
46 (39)
The injuries are divided into traumatic or overuse injuries and categorised as mild (1–7 days absence from floorball), moderate (8–29 days absence from floorball), or severe (>30 days absence from floorball), n number (per cent)
two groups (intervention group and control group) for male as well as female players. A descriptive analysis showed a positive skewed distribution of the data (2.3 ± 0.1). Therefore, a nonparametric analysis, the Mann–Whitney U test, was chosen for the inferential statistics. The effect size for the nonparametric test was calculated with the equation r = z/√N [12], where z is the z distribution and N is the sample size of the study. To compare the calculated effect size with other effect sizes (e.g. Cohen’s d), the formula d = 2r/√(1 − r2) was used [12]. Student’s t test was used when comparing the cohort and the dropouts in terms of age and years in floorball. The effect size for t tests was calculated with the equation eta squared = t2/t2 + (N1 + N2 − 2) [10]. The results were considered to be statistically significant if p was less than 0.05 and 95 % confidence interval (CI).
Results The evaluation of the present intervention during the first season has previously been reported elsewhere [39]. Results after season two In total during the second season, with trauma and overuse injuries combined, 93 players (27 %) out of the 346 players sustained 119 injuries during the game season (0.34 injury/player, 95 % CI 0.28–0.43), the intervention group 0.31 (95 % CI 0.22–0.39), and the control group 0.41 (95 % CI 0.29–0.53). In the intervention group, 29 % of the male players and 30 % of the female players were injured. In the control group, 40 % of the male players and 36 % of the female players were injured. The injury frequency showed that the total number of injuries was fewer in the intervention group than the control group. The frequency of severe injuries was 46 % lower in the intervention group. The female players in the intervention group sustained fewer overuse injuries than the females in the control group (Table 3).
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The inferential analysis of data from the second season in the intervention group and the control group did not show any statistically significant differences regarding injury rates, and the effect sizes of Cohen’s d were 0.1 or below. Both male and female players in the intervention group had a lower injury incidence compared to the corresponding figures in the control group (Table 4). Results of the two seasons together When comparing the injury rates during the whole study period, from the start of the first season to the end of the second season, neither the total number of injuries nor when injuries were divided into traumatic and overuse, nor separated by gender, showed any statistically significant differences between groups. For instance, the analysis of the injuries as one unit in the intervention group (Md = 1, n = 175) and the control group (Md = 1, n = 171) showed U = 14,183.5, z = −0.89, p = 0.37, r = 0.05, and Cohen’s d = 0.1. The effect size of the influence of the psychological skills training was considered to be small, with Cohen’s d = 0.2 for traumatic injuries, also for male and female separately. Cohen’s d = 0.2 was also shown for overuse injuries in male players and for all injuries combined. The corresponding effect sizes in other calculations were smaller than 0.2.
Discussion The most important finding in this study was that a lower number of players sustained fewer injuries in the intervention group compared to the control group during the second season. The two-season evaluation of a psychological injury prevention intervention showed a small effect (d = 0.2) for traumatic and overuse injuries in male players in the intervention group. The effect size was the same (d = 0.2) in female players in the intervention group for
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Table 4 Injury rates (numbers and percentage per season) for the intervention group and the control group by gender Season 1a
Season 2
Intervention Male
Control Female
Male
Intervention Female
Male
Control Female
Male
Female
Players (n)
94
99
109
99
87
88
87
84
Exposure (h) Injuriesb Injury incidencec
16,155 47 (24) 2.9 (2.2–3.8)
15,180 40 (20) 2.6 (1.9–3.6)
17,910 51 (26) 2.8 (2.1–3.7)
15,000 59 (30) 3.9 (3.0–5.0)
14,877 25 (21) 1.7 (1.0–2.7)
13,728 26 (22) 1.9 (1.1–2.9)
14,964 31 (26) 2.1 (1.3–3.2)
12,852 37 (31) 2.9 (1.9–4.2)
Injury/playerd
0.5 (0.3–0.7)
0.4 (0.3–0.5)
0.5 (0.3–0.6)
0.6 (0.4–0.8)
0.3 (0.2–0.4)
0.3 (0.2–0.4)
0.4 (0.2–0.5)
0.4 (0.2–0.7)
h hours, n number a
These results from season 1 have been published previously [40]
b
Number of injuries (percentage of total number of injuries per season)
c
Injuries/1,000 exposure hours (CI 95 %)
d
Injuries/player, means (CI 95 %)
traumatic and overuse injuries combined and for traumatic injuries separately. The effect size of the intervention’s influence is small but has increased for the abovementioned groups despite that no intervention was provided the second year. The rationale for using a group-based intervention including the entire team was that all team members would get the same education and be able to discuss and maintain the skills after the intervention was finished. This intervention comprised six sessions, which is similar to other psychological injury studies [7, 22, 25, 34]. Probably, the most effective intervention is when someone close to the team continues the psychological skills training that were implemented in order to maintain continuity and competence with the training. The result of injuries/player in the intervention group, 0.34 in this study, is equal to 0.34 [37] or lower, which is 0.49 [39] lower than in earlier floorball studies. The injury incidence (per 1,000 exposure hours) in the present study decreased in both groups after the second season. The incidence of injuries (1.9) in female players in the intervention group during the second season was lower than in female players in the control group for both the second season (2.9) and the first season (3.9) [39]. An increased awareness of the need for preventions strategies in elite floorball may have had an impact on the overall reduction of injuries. The severe injuries are the most important ones for prevention, and many studies have focused on ACL injury prevention [28, 33, 35]. This study did not, however, focus on level of injury severity or ACL injuries, in particular. At this time, there is no evidence in floorball that psychological variables contribute more to risk levels when it comes to severe injuries (e.g. ACL ruptures) even though there were 46 % fewer severe injuries in the intervention group after the second season. This result is important because severe injuries probably are those that influence the athlete
the most, not only through experiences of pain, but also due to absence from sport. Moreover, severe injuries may lead to athletes’ careers ending; also, at elite levels, these injuries are expensive for both athletes and society. The results showed that fewer players in the intervention group sustained fewer numbers of injuries than players in the control group over the two seasons. The decrease of injuries is therefore likely to play a significant role from a clinical point of view. Previous injury has been reported to be a risk factor for re-injury [16]. Hence, prevention of the occurrence of new injuries as well as re-injuries is important from both clinical and health economic perspectives. The injury registration in this study distinguished between overuse injuries and traumatic injuries. The injuries were defined by time-loss, which may not capture many overuse injuries because many players continue to play with overuse complaints [5, 38]. During the second season, 40 % of the injuries were overuse injuries. The choice of the present intervention was based on earlier studies discussing stress and injury relationships suggested by Williams and Andersen [22, 42]. Stress has been suggested to cause an acute response which might influence the risk of traumatic injury. The results of the present study showed a small effect of the intervention for traumatic injuries in both genders and in overuse injuries in male players. It is possible that the floorball players experience stress over time along with other kinds of stress responses besides the acute stress response. The allocation to the groups was not blinded, which might be considered a limitation. True experimental design with random assignment to groups in a study such as this one, however, would actually introduce problems that would undermine the study’s findings such as contamination across members of the team who did and did not receive the intervention or some members of a team feeling left out while others receive more attention. When evaluating injury prevention
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in ecological contexts, quasi-experimental methods are often preferred over true experimental designs [11]. The baseline information did not show differences between the two groups [39]. The cohort consisted of 82 % of the available teams at the start of this study. A limitation of this study was that players dropped out, and the inferential statistics were therefore restricted to a lower number of participants during the second season (n = 346). Even though the dropout analysis did not show statistical differences, and the dropouts were considered missing at random, the comparisons between the two studied seasons might be disparate. Solutions like “last value carried forward” or “list wise deleting” are both suggested in the literature but might change the result when making an assumption that uninjured players remain without injuries and that injured players sustain the same number of injuries during the following season [36]. The 13 % dropout rate did not, however, influence the present study where the power analysis showed a need of n = 64 in each group. Even though players dropped out from the study, the teams’ staff reported the injuries in the remaining players. Another limitation was that although the teams were included as a cluster to avoid spill over effects [8, 9], the risk of spill over, i.e. contamination between study groups, eventually arose between the two studied seasons. This might have been the case when some players and coaches were transferred to other teams, belonging to the opposite group, the intervention or control. In earlier studies, the importance of injury definitions [18] and recurrent events [13, 14] has been discussed. This was not defined in the present study and must be considered as a limitation. One of the limitations in the statistical analysis was the unmeasured confounding variables from, e.g., training content. A further limitation is that the practice and compliance with the intervention strategies or how the intervention teams used the psychological skills has not been evaluated. The clincial relevance of this study is the potential longterm effect of a psychological skills training intervention evaluated in a reduction of traumatic and overuse injuries. This will encourage coaches and medical teams to include psychology in the preventive strategies. The person who implements the intervention, in this case a sport psychology consultant, probably has a substantial influence on the outcome, and it is therefore interesting to evaluate this influence in future research. Other suggestions for future research are to evaluate the experience of stress and life events in floorball players along with further investigation of injury mechanisms in terms of overuse injuries and their prevention. Also, further research is suggested to investigate the costs of injuries in sport.
Conclusion It is valuable to study possible behavioural changes following injury prevention after a period of time. In the
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present study, elite floorball players were evaluated at two consecutive seasons after a psychological skills training programme. This group-based training showed a small effect size after the second year resulting in fewer injuries in total, but also fewer severe injuries in the intervention group compared to the control group. It is therefore important not to overlook the potential of a group-based psychological injury prevention programme. Acknowledgments Grants to accomplish this study were provided from Sophiahemmet Foundation, the Swedish Naprapathic Association, and Swedish National Centre for research in Sports. Thanks to the Swedish Floorball Federation and the participating coaches, players, and their medical staff.
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SPORTS MEDICINE
Sports injury prevention in Swedish elite floorball players: evaluation of two consecutive floorball seasons Ulrika Tranaeus · Urban Johnson · Andreas Ivarsson · Björn Engström · Eva Skillgate · Suzanne Werner
Received: 8 August 2014 / Accepted: 27 October 2014 / Published online: 2 November 2014 © European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA) 2014
Abstract Purpose The objective was to evaluate the effect of a psychological group-based injury prevention, which was implemented throughout the first season, after the second season, in Swedish elite floorball teams (males and females). The secondary objective was to evaluate the effect of the intervention over the two consecutive floorball seasons as a whole. Methods Twenty-three teams in the premier leagues for males and females volunteered and were allocated to an intervention group, n = 175 players, and a control group n = 171 players. The intervention group participated in psychological skills training during the first season. The control group did not receive any alternative treatment. Neither of the groups received any intervention during the second season. All injuries were registered and documented
U. Tranaeus · U. Johnson · A. Ivarsson Center of Research on Welfare, Health and Sport, Halmstad University, Halmstad, Sweden U. Tranaeus · B. Engström · S. Werner Department of Molecular Medicine and Surgery, Stockholm Sports Trauma Research Center, Karolinska Institutet, Stockholm, Sweden U. Tranaeus (*) · B. Engström · S. Werner Capio Artro Clinic, Sophiahemmet, Box 5605, 114 86 Stockholm, Sweden e-mail: [email protected] E. Skillgate Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden E. Skillgate Scandinavian College of Naprapathic Manual Medicine, Stockholm, Sweden
according to time-loss definition and classified into either traumatic or overuse injuries. Results Ninety-three players (27 %) sustained 119 injuries during the second season. The intervention group 0.31 (95 % CI 0.22–0.39) and the control group 0.41 (95 % CI 0.29–0.53) injuries/player. The injury incidence decreased in the intervention group and was lower than the control group. The analysis showed no statistical differences when comparing the intervention group and the control group neither after the second season nor after the two seasons together, Cohen’s d 0.2. Conclusion This group-based training showed a small effect size after the second year resulting in fewer injuries, especially severe injuries, in the intervention group compared to the control group. It is, therefore, important not to overlook the potential of a group-based psychological injury prevention programme. Level of incidence II. Keywords Athletic injury · Behaviour · Overuse injury · Psycho-education · Traumatic injury
Introduction The high incidence of injuries in sports is well documented, [2, 3, 19] showing a need for prevention of sports injuries [17, 31]. Previous studies on injury prevention suggest the use of research frameworks [4, 40] approached from different angles, for instance, implementation issues [11] and behavioural matters [41]. Most prevention research evaluates the effect of the intervention immediately after or close to the completion of the intervention. Successful injury prevention should work in the long-term perspective. Subsequently, this requires an evaluation after longer period of
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time. Therefore, in the present study, evaluation of the first season’s intervention of psychological skills training [39] has been performed at the end of the second consecutive season. Documentation of psychological factors as predictors for sport injuries has been reported in previous research [20, 22]. This is in line with theoretical models suggesting that some psychosocial and historical variables may be risk factors for injuries [1, 42]. These risk factors may be present along with many other intrinsic factors (e.g. age, gender, skill level [1]). Stress has also been reported to be a source of injuries [6, 15, 29]. Stress levels are discussed as being influenced by one’s history of stress, personality factors that predispose people to have substantial stress responses, and coping recourses [42]. Accordingly, studies on injury prevention aimed to reduce perceived stress levels, as well as stress reactions, have been conducted [23]. Three studies [25, 30, 34] used relatively long time frames for an evaluation after the end of an intervention (12 weeks or a completed sport season), whereas three other studies evaluated the intervention immediately after the intervention was finished [7, 21, 24]. These studies further showed the potential effect of using psychological interventions to prevent sport injuries and reduce the time-loss from sport due to injury. None of these studies, however, consisted of large cohorts. To our knowledge, only a few intervention studies have evaluated preventive effects after a longer period of time (e.g. a second season or more) [26, 27], and none of these studies evaluated a psychological intervention focusing on injury incidence in consecutive seasons. Floorball is an indoor team sport with a growing number of players worldwide. The rules and game format are the same for both male and female teams. Three previous studies on floorball reported seasonal incidences of 0.34 injuries/player in males and females [37], 0.46 injuries/player in females [32], and 0.49 injuries/player in males and females [39], respectively. Two injury prevention studies have previously been performed in high-level floorball players [33, 39]. Neuromuscular leg training for female floorball players reduced the injury risk to the lower
extremity by 66 % in an intervention group (n = 256) compared to a control group (n = 201) [33]. A psychological skills training programme including male and female floorball players did not result in significant differences between an intervention group (n = 193) and a control group (n = 208) at the end of the season [39]. Injury prevention strategies are implemented to influence a behavioural change with a long-term goal to reduce as many injuries, in as many athletes, as possible [11]. The hypothesis is that a psychological skills training programme might reduce the number of injuries after a consecutive season. Therefore, it is of clinical relevance to evaluate such an intervention over a longer period, e.g. the consecutive season, and injuries as one unit and to separate traumatic and overuse injuries due to their different injury mechanisms [1, 40]. To our knowledge, no second-season follow-up study of a psychological group intervention has been published earlier. The primary objective with the present study was to evaluate injury prevention of a psychological skills training group-based intervention programme, the season after the implementation (i.e. at the end of the second season in elite floorball teams for males and females). The secondary objective was to evaluate the effect of the intervention over the two consecutive floorball seasons as a whole.
Materials and methods This prospective study was carried out during the seasons 2010/2011 and 2011/2012 in the Swedish Floorball Federation’s elite leagues. The leagues consist of 28 teams, 14 male teams and 14 female teams. Twenty-three teams, 11 male teams and 12 female teams, totalling 346 players (174 males and 172 females), volunteered to participate in the study during the two seasons with completed injury records (Table 1). These players fulfilled the inclusion criteria, which were to understand the Swedish language; to be able to respond on psychometric instruments and questionnaires; and, for the intervention group, to participate in
Table 1 Gender-specific characteristics of the study participants Intervention group (n = 175)
Control group (n = 171)
Age Floorball experiencea Injured players, Season 1b
Male (n = 87) 23.9 ± 3.9 14.4 ± 3.4 34 (39 %)
Female (n = 88) 22.0 ± 4.9 12.3 ± 3.1 33 (37 %)
Male (n = 87) 24.9 ± 4.5 13.7 ± 4.6 40 (46 %)
Female (n = 84) 22.8 ± 4.4 11.9 ± 3.2 35 (42 %)
Exposure hours to floorball per weekc
6.1 ± 0.6
6.1 ± 1.0
6.2 ± 0.9
6.7 ± 0.7
Gender a
a
Mean years and standard deviation
b
Season 2010/2011
c
Mean hours/week and standard deviation during game season
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a provided psychological intervention programme. During the study, 55 players (13 %) dropped out. This was because they stopped playing floorball (n = 27) or they belonged to teams that did not report the injuries during the second season [e.g. transferred to teams abroad or to teams in Sweden with no or new medical staff (n = 28)]. The analysis of the dropouts showed no significant differences in age, floorball experience, previous injuries, or exposure to floorball (Table 2). The cohort was closed, meaning that new players coming into any of the teams were not included in the analysis. Procedure The Swedish Floorball Federation gave the approval to conduct this study. In springtime 2010, the coaches gave their approval to their teams’ participation and the athletes made the final decision to participate. The athletes received verbal and written information regarding the study and its purpose. Those athletes that participated gave their written consent to participate, contact information, baseline information, and completed psychometric instruments (reported elsewhere). The teams’ medical staffs were asked to document injuries starting from preseason training and continuously onwards through the two seasons. The hours of exposure were calculated from time periods involved in compulsory floorball training and games during preseason and competitive season. The teams were consecutively allocated to an intervention group n = 11 (males n = 94, females n = 99) or a control group n = 12 (males n = 109, females n = 99) by the first author [26]. At the same time as the teams reported that they accepted to participate in the study, they were asked to participate in the intervention group. This procedure continued until eleven teams were included. The players in the intervention group took part in a psychological skills training programme starting in the fall of the first study season, 2010/2011, whereas Table 2 Characteristics of the players that participated and those players that dropped out in-between the two seasons Players (n = 346)
Dropouts (n = 55)
p value Effect size
Agea
22.4 ± 4.2 Injuries presea- 0 (0–2) son (n) 1b
22.8 ± 4.9 0 (0–2)
n.s n.s
0.001c 0.18d
Injuries season 0 (0–6) (n) 1b
0 (0–3)
n.s
0.16d
Years in floorball (n)a
11.4 ± 4.9
n.s
0.003c
12.2 ± 3.5
n = number a Mean and standard deviation, and d Cohen’s d
b
median (range), effect size: c eta2
the players in the control group did not receive this or any other intervention. The psychological skills training programme was conducted by external sport psychology consultants. During the second preseason and full-game season, 2011/2012, all teams, irrespective of group membership, were prospectively followed without any intervention. The medical staff for each team continued to record injuries throughout the second season. Injury surveillance Injuries were defined as time-loss events with the following categories: mild (1–7 days absence from regular training or games), moderate (8–30 days absence from regular training and games), and severe (absence from floorball for more than 30 days) [43]. Injuries were also classified into traumatic injuries and overuse injuries [13]. The teams were offered the use of the Swedish National Injury Register. This web-based on-line registration was customised to fit the present study and was provided to all teams by the Swedish Floorball Federation. Intervention Sessions covering somatic and cognitive contents: e.g. relaxation, stress management, control of emotions, and goal setting were used to equip the teams with strategies to reduce the stress response (according to Williams and Andersen’s stress injury model) [42]. The intervention was developed to educate the entire team (players and staff) at the same time and was provided by sport psychology consultants. Appointments for sessions were scheduled to fit the team. The interventions were tailored for elite floorball and consisted of six meetings developed to last approximately 1 h each; details are presented elsewhere [39]. The present study was approved by the Regional ethical board, Karolinska Institutet, Stockholm, Sweden, Dnr 2009/2001-31. Statistical analysis An a priori sample size calculation was preformed to find out the number of participants needed to reach a power of 0.8. For this calculation, alpha was set to 0.05. Furthermore, the sample size was based on both the results of earlier studies [21, 25, 39] and the context. The estimated Cohen’s d effect size was 0.5 (a moderate effect size). Including these statistics into a power analysis results showed in an estimate that a minimum of 64 participants, in each group, were needed to reach sufficient power (β = 0.8). The data were analysed using IBM, SPSS version 20 to investigate injury incidence, differences in injury rates (injuries/1,000 exposure hours), and kinds of injuries between the
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Table 3 The injury frequency and proportions (percentage of total) Intervention Male (n = 87)
Control Female (n = 88)
Trauma Overuse Trauma Overuse Mild Moderate Severe
4 10 4
3 1 3
Total n (%) 18 (15) 7 (6)
9 4 2
7 4 0
15 (12) 11 (9)
Total
Total (n = 175)
Male (n = 87)
23 (19) 19 (16) 9 (8)
6 6 8
51 (43)
20 (17) 11 (9)
Female (n = 84)
Trauma Overuse Trauma Overuse 6 2 3
15 2 3
14 0 3
20 (17) 17 (15)
Total (n = 171)
All (n = 346) Trauma n (%)
Overuse n (%)
41 (34) 10 (8) 17 (14)
34 (29) 22 (18) 17 (14)
30 (25) 7 (6) 9 (8)
68 (57)
73 (61)
46 (39)
The injuries are divided into traumatic or overuse injuries and categorised as mild (1–7 days absence from floorball), moderate (8–29 days absence from floorball), or severe (>30 days absence from floorball), n number (per cent)
two groups (intervention group and control group) for male as well as female players. A descriptive analysis showed a positive skewed distribution of the data (2.3 ± 0.1). Therefore, a nonparametric analysis, the Mann–Whitney U test, was chosen for the inferential statistics. The effect size for the nonparametric test was calculated with the equation r = z/√N [12], where z is the z distribution and N is the sample size of the study. To compare the calculated effect size with other effect sizes (e.g. Cohen’s d), the formula d = 2r/√(1 − r2) was used [12]. Student’s t test was used when comparing the cohort and the dropouts in terms of age and years in floorball. The effect size for t tests was calculated with the equation eta squared = t2/t2 + (N1 + N2 − 2) [10]. The results were considered to be statistically significant if p was less than 0.05 and 95 % confidence interval (CI).
Results The evaluation of the present intervention during the first season has previously been reported elsewhere [39]. Results after season two In total during the second season, with trauma and overuse injuries combined, 93 players (27 %) out of the 346 players sustained 119 injuries during the game season (0.34 injury/player, 95 % CI 0.28–0.43), the intervention group 0.31 (95 % CI 0.22–0.39), and the control group 0.41 (95 % CI 0.29–0.53). In the intervention group, 29 % of the male players and 30 % of the female players were injured. In the control group, 40 % of the male players and 36 % of the female players were injured. The injury frequency showed that the total number of injuries was fewer in the intervention group than the control group. The frequency of severe injuries was 46 % lower in the intervention group. The female players in the intervention group sustained fewer overuse injuries than the females in the control group (Table 3).
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The inferential analysis of data from the second season in the intervention group and the control group did not show any statistically significant differences regarding injury rates, and the effect sizes of Cohen’s d were 0.1 or below. Both male and female players in the intervention group had a lower injury incidence compared to the corresponding figures in the control group (Table 4). Results of the two seasons together When comparing the injury rates during the whole study period, from the start of the first season to the end of the second season, neither the total number of injuries nor when injuries were divided into traumatic and overuse, nor separated by gender, showed any statistically significant differences between groups. For instance, the analysis of the injuries as one unit in the intervention group (Md = 1, n = 175) and the control group (Md = 1, n = 171) showed U = 14,183.5, z = −0.89, p = 0.37, r = 0.05, and Cohen’s d = 0.1. The effect size of the influence of the psychological skills training was considered to be small, with Cohen’s d = 0.2 for traumatic injuries, also for male and female separately. Cohen’s d = 0.2 was also shown for overuse injuries in male players and for all injuries combined. The corresponding effect sizes in other calculations were smaller than 0.2.
Discussion The most important finding in this study was that a lower number of players sustained fewer injuries in the intervention group compared to the control group during the second season. The two-season evaluation of a psychological injury prevention intervention showed a small effect (d = 0.2) for traumatic and overuse injuries in male players in the intervention group. The effect size was the same (d = 0.2) in female players in the intervention group for
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Table 4 Injury rates (numbers and percentage per season) for the intervention group and the control group by gender Season 1a
Season 2
Intervention Male
Control Female
Male
Intervention Female
Male
Control Female
Male
Female
Players (n)
94
99
109
99
87
88
87
84
Exposure (h) Injuriesb Injury incidencec
16,155 47 (24) 2.9 (2.2–3.8)
15,180 40 (20) 2.6 (1.9–3.6)
17,910 51 (26) 2.8 (2.1–3.7)
15,000 59 (30) 3.9 (3.0–5.0)
14,877 25 (21) 1.7 (1.0–2.7)
13,728 26 (22) 1.9 (1.1–2.9)
14,964 31 (26) 2.1 (1.3–3.2)
12,852 37 (31) 2.9 (1.9–4.2)
Injury/playerd
0.5 (0.3–0.7)
0.4 (0.3–0.5)
0.5 (0.3–0.6)
0.6 (0.4–0.8)
0.3 (0.2–0.4)
0.3 (0.2–0.4)
0.4 (0.2–0.5)
0.4 (0.2–0.7)
h hours, n number a
These results from season 1 have been published previously [40]
b
Number of injuries (percentage of total number of injuries per season)
c
Injuries/1,000 exposure hours (CI 95 %)
d
Injuries/player, means (CI 95 %)
traumatic and overuse injuries combined and for traumatic injuries separately. The effect size of the intervention’s influence is small but has increased for the abovementioned groups despite that no intervention was provided the second year. The rationale for using a group-based intervention including the entire team was that all team members would get the same education and be able to discuss and maintain the skills after the intervention was finished. This intervention comprised six sessions, which is similar to other psychological injury studies [7, 22, 25, 34]. Probably, the most effective intervention is when someone close to the team continues the psychological skills training that were implemented in order to maintain continuity and competence with the training. The result of injuries/player in the intervention group, 0.34 in this study, is equal to 0.34 [37] or lower, which is 0.49 [39] lower than in earlier floorball studies. The injury incidence (per 1,000 exposure hours) in the present study decreased in both groups after the second season. The incidence of injuries (1.9) in female players in the intervention group during the second season was lower than in female players in the control group for both the second season (2.9) and the first season (3.9) [39]. An increased awareness of the need for preventions strategies in elite floorball may have had an impact on the overall reduction of injuries. The severe injuries are the most important ones for prevention, and many studies have focused on ACL injury prevention [28, 33, 35]. This study did not, however, focus on level of injury severity or ACL injuries, in particular. At this time, there is no evidence in floorball that psychological variables contribute more to risk levels when it comes to severe injuries (e.g. ACL ruptures) even though there were 46 % fewer severe injuries in the intervention group after the second season. This result is important because severe injuries probably are those that influence the athlete
the most, not only through experiences of pain, but also due to absence from sport. Moreover, severe injuries may lead to athletes’ careers ending; also, at elite levels, these injuries are expensive for both athletes and society. The results showed that fewer players in the intervention group sustained fewer numbers of injuries than players in the control group over the two seasons. The decrease of injuries is therefore likely to play a significant role from a clinical point of view. Previous injury has been reported to be a risk factor for re-injury [16]. Hence, prevention of the occurrence of new injuries as well as re-injuries is important from both clinical and health economic perspectives. The injury registration in this study distinguished between overuse injuries and traumatic injuries. The injuries were defined by time-loss, which may not capture many overuse injuries because many players continue to play with overuse complaints [5, 38]. During the second season, 40 % of the injuries were overuse injuries. The choice of the present intervention was based on earlier studies discussing stress and injury relationships suggested by Williams and Andersen [22, 42]. Stress has been suggested to cause an acute response which might influence the risk of traumatic injury. The results of the present study showed a small effect of the intervention for traumatic injuries in both genders and in overuse injuries in male players. It is possible that the floorball players experience stress over time along with other kinds of stress responses besides the acute stress response. The allocation to the groups was not blinded, which might be considered a limitation. True experimental design with random assignment to groups in a study such as this one, however, would actually introduce problems that would undermine the study’s findings such as contamination across members of the team who did and did not receive the intervention or some members of a team feeling left out while others receive more attention. When evaluating injury prevention
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in ecological contexts, quasi-experimental methods are often preferred over true experimental designs [11]. The baseline information did not show differences between the two groups [39]. The cohort consisted of 82 % of the available teams at the start of this study. A limitation of this study was that players dropped out, and the inferential statistics were therefore restricted to a lower number of participants during the second season (n = 346). Even though the dropout analysis did not show statistical differences, and the dropouts were considered missing at random, the comparisons between the two studied seasons might be disparate. Solutions like “last value carried forward” or “list wise deleting” are both suggested in the literature but might change the result when making an assumption that uninjured players remain without injuries and that injured players sustain the same number of injuries during the following season [36]. The 13 % dropout rate did not, however, influence the present study where the power analysis showed a need of n = 64 in each group. Even though players dropped out from the study, the teams’ staff reported the injuries in the remaining players. Another limitation was that although the teams were included as a cluster to avoid spill over effects [8, 9], the risk of spill over, i.e. contamination between study groups, eventually arose between the two studied seasons. This might have been the case when some players and coaches were transferred to other teams, belonging to the opposite group, the intervention or control. In earlier studies, the importance of injury definitions [18] and recurrent events [13, 14] has been discussed. This was not defined in the present study and must be considered as a limitation. One of the limitations in the statistical analysis was the unmeasured confounding variables from, e.g., training content. A further limitation is that the practice and compliance with the intervention strategies or how the intervention teams used the psychological skills has not been evaluated. The clincial relevance of this study is the potential longterm effect of a psychological skills training intervention evaluated in a reduction of traumatic and overuse injuries. This will encourage coaches and medical teams to include psychology in the preventive strategies. The person who implements the intervention, in this case a sport psychology consultant, probably has a substantial influence on the outcome, and it is therefore interesting to evaluate this influence in future research. Other suggestions for future research are to evaluate the experience of stress and life events in floorball players along with further investigation of injury mechanisms in terms of overuse injuries and their prevention. Also, further research is suggested to investigate the costs of injuries in sport.
Conclusion It is valuable to study possible behavioural changes following injury prevention after a period of time. In the
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present study, elite floorball players were evaluated at two consecutive seasons after a psychological skills training programme. This group-based training showed a small effect size after the second year resulting in fewer injuries in total, but also fewer severe injuries in the intervention group compared to the control group. It is therefore important not to overlook the potential of a group-based psychological injury prevention programme. Acknowledgments Grants to accomplish this study were provided from Sophiahemmet Foundation, the Swedish Naprapathic Association, and Swedish National Centre for research in Sports. Thanks to the Swedish Floorball Federation and the participating coaches, players, and their medical staff.
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