In this longitudinal study on sport school students, one in every two students reported having frequent pain at baseline or at the two-year follow-up. Girls were at higher risk of having frequent pain at follow-up than boys. Being pre PHV at baseline was a risk factor for boys, whereas having frequent pain in two or more body regions and reporting a worse health status at baseline were risk factors for girls for belonging to the frequent pain group two years later. Participation in non-contact sports was a risk factor for having frequent pain at follow-up in both boys and girls. Having frequent pain at follow-up was associated with a worse sports performance at follow-up in boys, but no associations between frequent pain and sports performance were found in girls.
The overall prevalence of pain in this study was similar to that reported in population-based studies [2, 10, 32]. Still, the finding that one in two adolescent athletes experienced frequent pain in our study is concerning, since physical activity from a public health point of view would be expected to lead to better health and less pain. Legault et al. [33] investigated the 6-month prevalence of pain in adolescent athletes and found a prevalence of 38%. The methodology used for measuring pain differs between studies with regard to frequency, duration, intensity, and localization, which probably contributes to the variation in pain prevalence reported.
The prevalence of frequent pain at follow-up was higher in girls than in boys in our study. Previous research has shown that girls are at higher risk of experiencing pain than boys [2, 10], which was reflected by our athletic sample as well. The over-representation of girls with pain remains to be explained, but it is possibly a combination of biological, psychological, and social considerations that governs the experiencing and persistence of pain in boys and girls.
Frequent pain at baseline was a risk factor for frequent pain at follow-up for girls in this study, but the number of regions with frequent pain was also of importance. Pain in two or more body regions was associated with having frequent pain two years later for girls. The same was not found for girls reporting pain in only one body region. For boys there was a similar trend as that seen in girls. A previous cohort study found high persistence rates of multisite pain over time in both boys and girls [12], and it is possible that a larger sample of boys in our study could have strengthen the analysis. Rathleff et al. [2] reported a prevalence of 30% for multisite pain, which is slightly lower than the prevalence of 40–46% seen in our study on adolescent athletes.
Having a worse health status at baseline was a risk factor for having frequent pain at follow-up in this study, which was an association that was only seen in girls. The association between pain and poorer health status is supported by the results of a population-based study on pain in adolescents [5]. Since the present study included both persistence and development of frequent pain over time, it is not possible to say whether or not a worse health status at baseline is predictive of pain in the future. Psychological symptoms in children and adolescents appear to be predictive of reporting musculoskeletal complaints two years later [34], which emphasizes the need for monitoring of health status and pain together more closely in adolescent athletes. The pressure to perform in sports may lead to pain, and pain that is not properly managed over time may lead to poorer health. Both athletes and their surrounding teams must recognize that pain management requires a bio-psychosocial approach [8]. Sustainability in the health of adolescent athletes is an important goal for youth sports [35].
In comparison with boys from the average and post PHV group, boys in the pre PHV group were at higher risk of being in the frequent pain group at follow-up. Interestingly, in a review on pain and maturity, Swain et al. [20] stated that there was not enough evidence to conclude that pain increases as maturity advances in general populations. Our finding of late maturing boys still reporting having pain after two years adds to the ongoing discussion about the relationship between pain and maturity, but it is uncertain whether our results are specific to late maturing boys enrolled in a competitive sports school or if late maturity per se might increase the risk for pain among adolescent boys in general. Further studies on both adolescent athletes and boys in general are required to improve our knowledge in this area.
In the present study, the students who participated in non-contact sports were more likely to report having frequent pain at the follow-up. A previous population-based study on adolescents [32] demonstrated that the risk of having frequent pain in specific regions varied depending on type of sport and sex. Boys in team sports, such as football and handball, had a lower risk of having neck and shoulder pain, but a higher risk of having lower extremity pain in comparison with non-active boys. This result was not seen in girls from team sports. Girls in endurance sports, such as cross-country skiing and running, had a lower risk of having neck and shoulder pain and low back pain than non-active girls, but for boys there were no differences in risk of pain between boys in endurance sports and non-active boys [32]. The type of sport and sex appears to be important when studying frequency and localization of pain and should be considered in future studies.
Pain and type of sport can also be discussed in relation to injuries. Overuse injuries appear to be more common in non-contact sports than in contact sports [36], which could be in line with the increased risk of pain seen in non-contact sport athletes in our study. Contact sports appear to be associated with a high risk of traumatic injuries [36]. Traumatic injuries usually include time lost from participation, and in this study the injured students were excluded mostly due to the fact that they could not participate in sports tests. The reported pain in this study is thus less likely to be due to current acute injuries. Hainline et al. [9] emphasized both pain management (the bio-psychosocial perspective) and injury management (focusing on the musculoskeletal state) for athletes, since pain may persist independently of injury—or after the tissue has healed. Since we studied the experience of pain regardless of cause, the results should be interpreted from this standpoint.
Frequent pain was found to be associated with a worse sports performance in the 20-m sprint and CMJ-AS at follow-up in boys. The same analysis (but controlled for maturity offset) was previously done for baseline, which showed similar results [6]. Since maturity offset is the most accurate around average PHV [16, 17], it was omitted from analysis at follow-up. Due to heterogeneity in the type of sports represented at the school and small differences in sports performance between pain groups, it is difficult to evaluate whether the negative effect of frequent pain on sports performance has any practical implications. Future studies of pain in athletic samples should assess functional ability in addition to questions about pain.
The limitations of this study should also be discussed. The drop-out rate from baseline to follow-up was 26%, but the students who were lost to follow-up did not differ significantly from the sample included regarding baseline variables. The study had to rely on the limited number of participants that could be included from this unique sport school, which may invoke a power problem in analyses with non-significant, although interesting, results. As an example, a post-hoc analysis with the observed absolute difference of 25% for the outcome of frequent pain in boys at follow-up, gave a statistical power of 60% based on two-tailed test with the statistical significance set to p-value < 0.05. Having a larger sample size might have given higher power in logistic regressions (where non-significant trends were identified in boys) and might have allowed multiple regression analyses, which could not be performed with the sample size used.
Adolescents admitted to the sports school were already pre-selected because of their sports talent, which could make it difficult to apply the results to a more general population [37]. It is also a limitation that time spent or intensity of training in regular club practices and competitions outside of school hours was not collected. This may vary depending on type and level of sports. The selected sports performance tests are commonly used when evaluating physical capacity in adolescents, but sports performance is a broader concept involving technical and tactical elements, which was not assessed in the present study.
Almost all the girls in this sport school study were classified as post PHV. It would have been interesting to determine how timing in physical maturity affected pain in girls, but since they were 13–14 years of age during their first year at the sport school (baseline), and girls generally reach PHV at the age of 12 [17], the study started too late to capture PHV in girls. Analyzing maturity offset as a continuous variable gave no further information.
To estimate maturity by anthropometric measurements and sex-specific equations in adolescents is an uncertain method in comparison with skeletal age assessments [38], but it is one of few non-invasive methods available. An update of maturity offset equations was published a few years ago [39], but was not used in the previously published cross-sectional study [6] or in the present longitudinal study. Analyses with the updated equations (data not shown) did not change the results from or the conclusions made in the present manuscript. Future studies in the field should take the various limitations with maturity estimation into consideration.
The study had several strengths that are worth highlighting. Firstly, the longitudinal study design enabled us to study risk factors for persistence or development of frequent pain over two years. Secondly, the study involved both boys and girls attending the same sport school, which proved to be valuable in terms of increasing our knowledge of sex-specific differences in risk factors for pain in adolescent athletes. Thirdly, a variety of sports were represented, which strengthened the applicability of the results.
Pain in childhood is associated with reporting of pain in young adulthood, and persistent pain has negative effects on physical, psychological, and social wellbeing. In the IOC consensus statement on pain management in athletes, it is emphasized that pain should be understood as a condition that is influenced by bio-psychosocial factors [9]. The results from the present study are in line with the IOCs recommendations, and give scientific support for parents and for the support staff surrounding the adolescent athlete in being observant of the increased risk of developing persistent pain. The findings can also assist in developing pain preventive interventions in adolescent athletes who are aiming for a future professional career. It is of utmost importance to recognize students who are at higher risk of developing pain early on, to prevent pain from becoming persistent.