Low back pain in female elite football and handball players compared with an active control group

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1 DOI /s SPORTS MEDICINE Low back pain in female elite football and handball players compared with an active control group Paula Tunås Agnethe Nilstad Grethe Myklebust Received: 2 July 2013 / Accepted: 6 May 2014 Ó Springer-Verlag Berlin Heidelberg 2014 Abstract Purpose The purpose of this cross-sectional study was to compare the prevalence of low back pain (LBP) among female elite football and handball players to a matched non-professional active control group. Methods The participants were requested to answer a questionnaire based on standardized Nordic questionnaires for musculoskeletal symptoms to assess the prevalence of LBP. Included participants were elite female football (n = 277) and handball players (n = 190), and a randomly selected control group from the Norwegian population (n = 167). Results Fifty-seven percentage of the football players, 59 % of the handball players and 60 % of the control group had experienced LBP the previous year. There were no significant group differences in the prevalence of LBP ever (p = 0.62), the previous year (p = 0.85) or the previous 7 days (p = 0.63). For both sports, there was a significant increase in prevalence of LBP from the resting period to the competitive periods of the season (p B 0.001). Seventy percent of the goalkeepers in both football and handball had experienced LBP the previous year. Conclusion There were no difference in LBP among female elite football and handball players compared with the control group. However, female elite athletes in football and handball reported a high prevalence of LBP compared to previous studies. The variations in LBP and playing positions indicate that specific field positions, P. Tunås (&) A. Nilstad G. Myklebust Department of Sports Medicine, Oslo Sports Trauma Research Centre, Norwegian School of Sports Sciences, PB 4014, Ullevål Stadion, 0806 Oslo, Norway paulatunas@hotmail.com in football and handball, is a risk factor for developing LBP. Level of evidence III. Keywords Low back pain Prevalence Female Elite athletes Football Handball Introduction Top-level sports require monotonous and repetitive demanding physical exercises and training with high loads on the spine, often from an early age [6]. Several studies have reported a high prevalence of LBP among elite athletes [4, 6, 15, 16, 18, 35, 36]. Existing literature has focused on sports with specific demands to the lower back, such as rowing [4, 33], gymnastics [7, 12, 21, 24, 35, 36], wrestling [6, 13, 24, 36], weight lifting [6, 13, 24, 29] and cross-country skiing [4, 10, 28]. There are also studies that have investigated the prevalence of LBP in team sports. Hoskins et al. [18] showed that elite rugby players were twice as likely to report daily or weekly LBP as a nonathletic group, and the prevalence of LBP increased with athletic level. Keene et al. [21] reported the incidence of back injuries in American football college players to be 17 per 100 participants. In a retrospective study on beach volleyball players, LBP was reported as the most common overuse injury [5]. Hangai et al. [16] also demonstrated a high rate of LBP in volleyball players (78 %), compared to control subjects (50 %). Baseball, basketball [16], ice hockey [6], tennis [16, 36] and male football [15, 16, 24, 26, 29, 30, 36] are other team sports that have reported a high prevalence of LBP. The origin of LBP can be a result of a traumatic as well as an overuse injury [30]. A traumatic injury refers to a

2 specific traumatic event leading to immediate interruption of training and competition or matches [8, 11]. An overuse injury is caused by micro-trauma over a long period of time without a single identifiable event of trauma and do not necessarily cause absence from training and competition [3, 8, 11, 30]. It is thereby possible that overuse injuries are underestimated in several sports, as many studies have used the time loss definition (an injury that results in a player being unable to take full part in future training or match play) or the medical attention definition (an injury that results in a player receiving medical attention) to report injuries [8, 11]. The effect of this may have contributed to inaccurate reports of prevalence of LBP in many sports. Traumatic injuries in the lower extremities, especially in knee and ankle have reported to be high in both football [20, 32, 37] and handball [23, 25, 31], while the prevalence of LBP has been given less attention and is poorly investigated. On the other hand, retrospective epidemiological studies reporting overuse injuries in football [20, 30, 32] and handball [31] have found LBP to be one of the most prevalent overuse injuries [20, 30 32]. Ristolainen et al. [30] presented LBP to be the most prevalent previous overuse injury (28 %) among football players. Few studies have compared the prevalence of LBP among football players with a control group [15, 16, 24, 38]. Two longterm follow-up studies found no differences in LBP in former male football players compared to non-athletes [24, 38]. In contrast, two cross-sectional studies, which included athletes from various sports, indicated a higher rate of LBP in football players than in a normal population [15, 16]. To our knowledge, no previous studies have examined the prevalence of LBP among elite handball players or among female elite football players, and little is known of what consequences football and handball play has on the lower back. Evaluating the prevalence of LBP among elite football and handball players is essential for developing prevention strategies. Increased knowledge on the prevalence of LBP will improve the development of prevention exercises and programs in the clinic. Thus, the purpose of the present study was to investigate the prevalence of LBP among female elite football and handball players, and to compare the result with a matched non-professional active group of women. Materials and methods This cross-sectional study is based on a survey among female elite football players ( ; 3 years), female elite handball players ( ; 5 years) and a female control group (2012) (Fig. 1). The survey was conducted as a part of a prospective cohort study aimed at investigating risk factors for ACL injuries in female elite football and handball players. The players participated in pre-season screening tests where they also completed a questionnaire regarding LBP. All players who completed the questionnaire and were years of age the year they were tested, were included in this study. A gender-matched control group (females aged 18 32) of 400 people was randomly selected from the Norwegian population by the National Register and included in the study. A similar questionnaire (without sports-specific questions) was sent by post to the control group. Subjects who did not return the questionnaire within 4 weeks were contacted by telephone and were asked to complete the questionnaire directly, or to return it by or post. To compare the elite-level athletes with a less athletic group, we excluded subjects from the control group who reported being competitive athletes training more than 5 times per week. We also excluded samples unable to speak or read Norwegian. The questionnaire The questionnaire was based on standardized Nordic questionnaires, which have been found valid, to study and compare the prevalence of occupational musculoskeletal symptoms in different groups and populations in the Nordic countries [1, 22]. The reliability of the questionnaire has been shown to be acceptable [22]. The Nordic questionnaire about LBP uses the following definition; pain, ache or discomfort in the lower back with or without radiation to one or both legs. The participants were requested to answer the questionnaire whether they had pain or not in the lower back, by marking the option closest to the true situation. Special information was given to exclude pain caused by the menstrual period. We included the following standard questions from the Nordic questionnaire: Have you ever experienced LBP? Have you experienced LBP during the previous 7 days? How many days during the past 12 months have you had LBP? Have you been examined or treated for LBP by a physician, physical therapist, chiropractor or other health personnel as an outpatient during the previous 12 months? Have you ever had to change your occupation or working assignments because of LBP? Have you ever had surgery because of LBP? Have you ever experienced radiating LBP? In addition to the standard questions, specific questions were elaborated. Most of these were based on sport-specific questions (thoroughly pilot tested) used in the study by Bahr et al. [4]. These questions are listed above:

3 What is your playing position on the court? How many seasons have you been playing at the elite level? How many hours have you trained during the past year (4 categories: \400 h/ h/ h/ [700 h)? How many days of training have you missed because of LBP during the past 12 months? How many matches have you missed because of LBP during the past 12 months? Have you experienced LBP during the following parts of the season: the resting period, the transitional period or the competitive season (4 categories: no/sometimes/ weekly/daily? Has the LBP been caused by contact with another player? In what involvement have you experienced LBP (3 categories: acute pain as a result of injury/pain over time as a result of overuse/both)? The control group answered the last specific question only. In addition, the control group answered questions about their training habits (number of weekly training sessions and eventual competitive sport). Questions regarding age, height and weight were also included for all three groups. Ethical approval The study was approved by the Regional Committee for Medical Research Ethics; South-Eastern Norway Regional Health Authority (ID number 2011/1999) and by the Norwegian Social Science Data Services (ID number 28757), Norway. All players signed a written informed consent form. Statistics The questionnaires were analysed using SPSS (v for Windows, SPSS, Evanston, Illinois). Subject characteristics are reported as means ± standard deviations, and differences were assessed using a one-way between-group analysis of variance (ANOVA). We compared LBP prevalence between groups with Chi-square tests (Pearson s chi-square or Fishers exact test, as appropriate). Wilcoxon signed rank test was used to test for changes in LBP prevalence across the season. Binary logistic regression analyses were used to test for interaction of the training volume in the two sports with regard to prevalence of LBP, adjusted for the parameters age, weight and height. The dependent variable was the prevalence of LBP the previous 12 months (yes/no), while yearly training volume was the independent variable and age, weight and height were covariates. We also used Binary logistic regression to assess whether seasons and playing positions on the court were potential predictive factors for developing LBP, with adjustments for age, height and weight. Low back pain in the previous 12 months (yes/no) was the dependent variable, and as independent variables we used seasons and playing positions. Odds ratios (OR) with 95 % confidence intervals (CI) are reported. p values equal to or below 0.05 were considered statistical significant. Results Participants Sample characteristics There were no differences in age between the football (22.4 ± 4) and the handball players (22.3 ± 3) (p = 0.92), but the control group (25.6 ± 4) was older compared to both the football (p = 0.001) and the handball players (p = 0.001; Table 1). The handball players were higher than the two other groups (p = 0.001), but there was no difference between the football players and the control group (p = 0.94). There were differences in weight between handball players and the control group (p = 0.01), between football players and the control group Table 1 Subject characteristics (n = 634) by group Fotball players n = 311 Answers n = 305 Included n = 277 Excluded n = 28 Football (n = 277) Handball players n = 206 Answers n = 203 Included n = 190 Total participants n = 634 Handball (n = 190) Excluded n = 13 Control group n = 400 Answers n = 170 Included n = 167 Fig. 1 Flowchart of included participants in the study Control group (n = 167) Age (years) 22.4 ± ± ± 4 Height (cm) ± ± ± 7 Weight (kg) 62.6 ± ± ± 14 Elite level (years) 3.1 ± ± 4 Results are shown as mean ± SD. Elite level: number of seasons (years) playing at the elite level in their sport Excluded n = 3

4 (p = 0.001), and between the football and handball players (p = 0.001). Prevalence of LBP Table 2 summarizes the responses to the LBP questionnaire. There were no differences in the prevalence of LBP among the groups. More than 60 % of the groups had experienced LBP ever. More than half of the participants had experienced LBP during the previous 12 months and % reported having experienced LBP the previous week. Figure 2 illustrates the prevalence of days of LBP the previous 12 months by group. Football and handball players reported having received significantly more outpatient medical assistance than the control group. Only 3.2 % (n = 6) of the handball players, 3.6 % (n = 10) of the football players and 4.9 % (n = 8) of the participants in the control group who reported having experienced LBP ever did not experience LBP the previous 12 months. More than 70 % of the football and handball players, who reported having experienced LBP ever, described the source of the LBP to be a result of overuse injury. Less than 10 % of the football and handball players Table 2 Responses (%) to the various LBP questions by group (n = 634) Football (n = 190) Handball (n = 277) Control group (n = 167) p value LBP ever (n = 634) (n.s) LBP previous 12 month (n = 629) (n.s) LBP previous 7 days (n.s) (n = 629) Sleeping problems (n.s) (n = 627) Medical assistance (n = 628) Surgery (n = 627) (n.s) Occupational change (n.s) (n = 628) Radiating LBP (n = 628) Gluteal region (n.s) Thigh (n.s) Knee (n.s) Lower leg or foot (n.s) Missed training (n.s) (n = 467) Missed competition (n = 467) (n.s) Prevalence of LBP (%) reported a traumatic injury as the source of the pain. When looking at the different playing positions on the court among football players, the highest prevalence was found for goalkeepers (71 %) and midfielders (67 %). For handball players, goalkeepers (70 %) and line players (63 %) had the highest prevalence. Low back pain related to playing situations was reported in 39 % of the football players and 41 % of the handball players. Football players experienced most LBP during landing, followed by shooting and turning/cutting. For handball players, the corresponding figures were shooting, followed by tackling and landing. Only 4.7 % (n = 13) of the football players and 6.3 % (n = 12) of the handball players reported that LBP was caused by a contact situation with another player. Midfielders (OR 2.5, CI ; p = 0.03) and goalkeepers (OR 3.04, CI ; p = 0.05) in football were more likely to experience LBP compared to strikers (Table 3). Number of years playing at elite level did not affect the risk of LBP. Training volume Football Handball Control group 0 days 1-7 days 8-30 days >30 days Daily Fig. 2 Prevalence of days of LBP (%) during the previous 12 months by group (n = 629) The total training volume during the previous 12 months for football and handball players is presented in Table 4. The training volume in the control group was reported; never 8.4 % (n = 14), once a week or less 19.2 % (n = 32), 1 2 times a week 31.1 % (n = 52), 3 4 times a week 29.3 % (n = 49), 5 times a week 8.4 % (n = 14) and 7 times a week 0.6 % (n = 1). The most common activity reported by the control group was fitness studio training. Training volume exceeding 700 h per year was related to less amount of LBP, but the relationship was not significant (OR 0.5; CI ; p = 0.28) (Table 5).

5 Table 3 Analysis of risk factors for LBP during the previous 12 months (yes/no) by sport group (n = 449) Variables Discussion Regressions coefficient 95 % confidence limits of odds ratio p value OR LB UB Seasons (years) (n = 438) (n.s) Football (n = 239) Striker Ref. Defender 0.37 (n.s) Midfielder Forward 0.41 (n.s) Goalkeeper Handball (n = 185) Line player Ref. Back (n.s) Wing (n.s) Goalkeeper 0.08 (n.s) OR odds ratio, LB lower bound, UB upper bound, Ref. reference group Table 4 Training volume during the previous 12 months by sport (n = 440) Football (n = 267) (%) Handball (n = 173) (%) Training volume (h) \ (5.2) 10 (5.8) (36.7) 46 (26.6) (37.8) 81 (46.8) [ (20.2) 36 (20.8) Table 5 Logistic regression analysis of LBP in the previous 12 months (yes/no) and yearly training volume among the two sports groups (n = 438) Variables Regression coefficient p value OR LB UB Training volume \400 Ref (n.s) (n.s) [ (n.s) OR odds ratio, LB lower bound, UB upper bound, Ref. reference group The main findings of the current study were that there were no differences in the prevalence of LBP among female elite football players, female elite handball players and the control group. Nevertheless, according to results reported in previous studies, there is a high frequency of LBP among female elite football and handball players. Furthermore, nearly three-quarters of the goalkeepers among both football and handball players reported to have had LBP the previous 12 months. The players also reported a noticeably higher amount of LBP during the competitive season. Prevalence of LBP Our findings conclude small differences when comparing the prevalence of LBP among the three groups. In spite of this, there was a relatively high cumulative and period prevalence of LBP in the two athletic groups compared to other studies. In our study, we found that 57 % of the football players and 59 % of the handball players had experienced LBP the previous 12 months. In the study by Bahr et al. [4], the prevalence of LBP the previous 12 months was reported to be 63 % among cross-country skiers, 55 % among rowers and 50 % among orienteers. Sward et al. [36] reported back pain among wrestlers, gymnasts, football players and tennis players at a frequency between 50 and 85 %. Of these 58 % of the football players reported LBP, which is consistent with our findings. A higher prevalence was reported by Hangai et al. [15, 16], where the lifetime prevalence of LBP was 62 and 77 %, respectively. However, the high prevalence of LBP in the control group in our study is not in accordance with previous findings [4, 15, 16, 18, 35]. Noteworthy, many out of previous studies have not used a randomly selected control group [15, 16, 18, 35], and the result can therefore not be generalized to the total population. Another explanation of the high prevalence of LBP in the control group could be related to the fact that the athletic level of our controls was relatively high. Direct comparisons between elite athletes and a less athletic population regarding LBP may be difficult, as highly motivated top athletes may ignore pain with the purpose of maintaining or progressing physical performance [35]. Reasons could be strictly competitiveness, economical or keeping their position in the team. Granhed & Morelli [13] stated that that tolerance of pain seemed to be higher among athletes than non-athletes. They investigated wrestlers, who are athletes used to body contact during combats probably leading to painful moments. Bahr et al. [4] also mentioned that athletes may have a higher threshold for reporting symptoms, as LBP may interfere more with sport performance than other daily activities. Alternatively, even low amounts of pain may impede athletic performance and thus affect the athlete to a greater extent than a non-athlete [35]. Experience of pain is subjective and will likely differ within groups and not only between groups.

6 The low back pain questionnaire Notable is the significant larger proportion of football and handball players who sought medical attention in cause of LBP than the control group. The same finding was reported by Bahr et al. [4], who suggested that the finding could be explained by severity of the injury in sports groups compared to the less athletic group or that an elite athletic population has easier access to professional care. It could also mirror the fact that elite athletes strive hard to get back to full participation in training sessions and competitions as soon as possible. Only a few football and handball players in this study reported contact with another player to be the cause of their LBP. These findings are similar to the study by Greene et al. [14], where a majority of the reported sports-related back injuries were caused by self-initiated actions. Most participants reporting LBP ever did also report LBP the previous 12 months. A previous history of LBP is documented to be a strong risk factor for future episodes of LBP [27, 34]. Furthermore, current LBP and a history of LBP during the previous 5 years may be a predictor for sustaining LBP in the following athletic season [14]. The majority within all three groups in our study reported the cause of the LBP to be a result of overuse injury. This finding is in accordance with previous studies, showing that LBP among football [20, 30, 32] and handball players [31] more often is a result of overuse rather than a traumatic injury [20, 30 32]. The frequent overuse estimation gives us an indication of the importance of reporting all types of injuries, and not only the time-loss injuries, which is commonly used in epidemiological studies [3]. In our study, we would have ended up with a lower prevalence of LBP if we had used the time-loss definition, since only % of the football and handball players reported missed training due to LBP. For match absence, the corresponding numbers would have been approximately 10 % in both groups. It is important to keep in mind that these results are self-reported and not fully reliable, as we do not have information from clinical examinations. Our results demonstrated that being a goalkeeper increased the likelihood for LBP. A total of 70 % of the goalkeepers in both football and handball had experienced LBP the previous 12 months. Ozturk et al. [26] found a significantly higher prevalence of osteophytes in the spine in former football players among goalkeepers and forward players compared to the other playing positions. The high prevalence of LBP among goalkeepers in our results may indicate a high physical load of the lumbar spine in this playing position. The goalkeeper s role in both football and handball involves quick reflexive actions to prevent scoring, as well as landings with unequal weight distribution with a great range of motions in the spine. It is possible that these elements affect the lower back in a negative way. Ozturk et al. [26] suggest that goalkeepers in football conduct movements involving hyperextension and rotation of the spine more frequently than other players, and these actions have been suggested as an aetiological factor to develop spondylolysis [9, 17, 19]. There is also evidence supporting rotational movements in occupational settings to be a risk factor for developing LBP [17, 39], which could theoretically also be applied to sport exercises. Many years of competing at a high level have been found to increase the prevalence of LBP [16], but our findings did not indicate any interaction between prevalence of LBP the previous year and number of seasons played at the elite level. Instead, we found a higher prevalence of LBP in the intense training and competitive season, which is in line with the observation by Bahr et al. [4], assuming that periods with higher amounts of football and handball play is stressing the lower back. When investigating the relationship between LBP the previous year and annual training volume for the football and the handball players, we did not find any significant correlation. Conversely, the interaction was rather a reduction in LBP with increased training volume. During the active resting period, we assume that players have less footballand handball-specific training sessions, since there are fewer matches at this time. Contrary, the players do more basic physiological training with focus on strength, coordination and condition. Related to this reflection, it can be assumed that there are movements and actions in the two sports contributing to LBP, such as twisting and high load, rather than the training volume. Methodological considerations There are some limitations to consider when interpreting the results from the current study. The main limitation is the low response rate among the control group (46 %). This might be explained by the fact that subjects without symptoms of LBP did not answer to the questionnaire to the same extent, even though the invitation letter clearly stated that we wanted the participant to complete the questionnaire whether they have had pain or not in their lower back. With this in mind, the prevalence of LBP in the control group may be overestimated. Another potential limitation is the relatively high activity level in the control group, which may mask potential differences between the groups. We used a retrospective registration design to collect information about LBP, and one challenge with studies employing a retrospective model is the threat of recall bias. The fact that the results are dependent on the memories of the participants may lead to underreporting of the prevalence of LBP. However, this problem is likely to affect all three groups in a similar manner. The information regarding

7 symptoms of LBP in the present study was collected with the Nordic questionnaires, which have been thoroughly assessed for reliability, validity and practical use [1, 22]. Nevertheless, as Bahr et al. [4] stated when they investigated endurance athletes, it should be noted that the Nordic questionnaires are developed to investigate the prevalence of musculoskeletal symptoms in occupational settings in different populations and not in a sporting context. In order to better correspond to athletes, we therefore applied sportspecific questions, as previously used by Bahr et al. [4]. Another factor to consider is the threat of sampling bias. In this case, the data collection was conducted in connection with pre-season screening tests of female elite football and handball players in Norway. An inclusion criteria for the screening tests was that the players needed to be free of injury and able to fully participate in training and matches with their team. Therefore, some players did not participate due to other injuries, and we do not know whether these had experienced LBP or not. Despite this, as we have been able to include a high number of football and handball players in the study, we assume that these players are a representative sample of female football and handball players at the top level in Norway. The analysis controlled for age, height, weight, seasons playing at the elite level, training volume and playing position on court. There may be other confounders which we were unable to control for, such as playing surface. Football players have shown a higher incidence of LBP when playing at artificial turfs compared to natural grass [2]. There are no data about playing surface, but with this study design, it is not possible to establish such a causeand-effect relationship. Moreover, there are no information about the athletes occupational work, even though most of these players have a full-time job in addition to playing football or handball. This may be an influencing factor, as frequent lifting [17, 40] and twisting [17, 39] in occupational setting are elements that have shown to increase tendency to develop LBP. The high prevalence of LBP among female elite football and handball players indicate the need for preventive core exercises and programs. This is important to keep in mind in the daily clinical work, and hopefully, this will lead to a reduction of the prevalence of LBP in these athletes. Further research should focus on investigating why some playing positions have a higher propensity of developing LBP. Increased knowledge on risk factors for LBP will improve the development of preventive strategies. 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