Association between low back pain and functional / kinetic aspects of surfers : disability , function , flexibility , range of motion and angle of the thoracic and lumbar spine

| Although surfing can contribute to chronic low back pain, the relationship between functional/kinetic changes and low back pain are still not fully understood. The association between low back pain and functional/ kinetic aspects was investigated in people who had surfed for different numbers of years, in a cross-sectional study involving 66 surfers from the coast of Paraná. The participants were allocated into three groups considering how long they had surfed: G1 (up to 4.9 years), G2 (from 5 to 9.9 years) and G3 (more than 10 years). The following items were evaluated: body mass index; level of physical activity; low back pain; intensity and frequency of low back pain, low back disability, low back function, low back flexibility, low back range of motion, low back and thoracic angles. To analyze the association between functional/ kinetic aspects and low back pain, Pearson’s Qui-Square Bazanella et al. Dor lombar e aspectos cinético-funcionais de surfistas 395 test was used for categorical data, while for nominal data ANOVA with Bonferroni’s post-hoc test (p<0.05) was used. The group which had surfed the longest (G3) showed an association with the occurrence of low back pain (p=0.05) and its highest intensity (p=0.01). The group with 5 to 9.9 years of surfing (G2) showed the largest low back angle (p=0.04). We conclude that the surfer’s chronic low back pain is associated with greater pain intensity, the angle of the lumbar curvature and how long the


INTRODUCTION
Surf is an intermittent type of sport that requires the person to alternate between high, moderate and low intensity activities 1 . It is performed by people of different ages and requires long periods of practice. Moreover, it requires a high level of neuromuscular ability and balance, with movements from higher and lower limbs and the spine 2 . Thus, pains and discomforts associated with the muscle demands of these movements from the sport may arise over time 3,4 .
Of the chronic muscle dysfunctions, lower back pain stands out among surfers from different countries 3,5,6 , at times making them find the sport intolerable or giving it up. In Brazil, chronic low back pain affects three of every 10 athletes who surf 7 . The higher incidence of low back pain in surfers in comparison with a group of sedentary people 8 reveals the need of specialized professional attention in the search for the kinetic/functional factors demanded by the sport.
Professional surfers who train most of their time present better control of their posture, especially in unstable surfaces 9 . Similarly, recreational surfing may cause beneficial adaptations to the neuromuscular function on the long term, with lower rates of posture oscillation in the standing position, with closed eyes and in a smooth surface 2 . However, when we compare amateur surfers with active individuals who perform different sports, there is no different in their balance control 10 . Thus, we conclude that lower back pain in surfers is not caused by posture instability, since higher rates of oscillation may be related to low back pain 11 .
However, isometric hyperextension while paddling 7 and doing the pop-up (quick movement to change from the position of paddling to standing up on the surfboard) 12 were mentioned as probable causes for lower back pain. As a result, our hypothesis is that kinetic and functional changes in the thorax and lower back could be related to pain in the area.
Up to the moment, we did not identify any study that investigated the association between low back pain and kinetic and functional factors in surfers. Thus, the present study aimed to investigate the relationship between the presence of lower back pain (and its intensity) and some of the variables of the kinetic/ functional condition of the region (lumbar disability caused by pain, lumbar function and flexibility, range of motion and angle of the thoracic and lumbar spine) in surfers from the coast of Paraná who had been surfing for different numbers of years.

METHODOLOGY
The participants of this cross-sectional study were professional, amateur or recreational surfers from the coast of Paraná who had been surfing for at least 6 months. They were from both sexes, and their age ranged between 18 and 42. We excluded individuals with peripheral neurological and vascular comorbidities, who had had back surgery less than a year before or who had a herniated disk and/or spine fractures.
For the sample calculation, we considered the percentage of surfers was 1.47% 13,14 (2,803,770) of the total of the population in Brazil (190.732.694), according to data from the last Census/IBGE 2010. When adopting these parameters, based on the equation of a previous study 14 , the result was 62 surfers, and 66 were selected (figure 1). The participants were allocated into three different experimental groups according to how long they had been surfing: group 1 (G1, up to 4.9 years of surfing, n=22), group 2 (G2, between 5 and 9.9 years of surfing, n =17) and group 3 (G3, more than 10 years of surfing, n=27). Table 1 shows the characteristics of the participants. All procedures carried out in this study were approved by the Research Ethics Committee (Statement 335,941).
The procedures of this study were carried out individually by a single inter-rater.
To characterize the participants, we used a demographic questionnaire which assessed: age, gender, surfing category, years of surfing, number of hours per day and weekly frequency of the surfing training.
The Body Mass Index (BMI) was obtained by dividing the mass of the individual by the square of their height (kg/m²) and the participants were classified as underweight, eutrophic, overweight or obese 15 .
The level of physical activity was investigated by the IPAQ (International Physical Activity Questionnairelong version) 16 and the participants were classified as sedentary, insufficiently active, active and very active.
Acute lower back pain was analyzed by asking if an episode of acute lower back pain had occurred in the previous four weeks, with its intensity being assessed with the 11-point pain intensity numerical rating scale (PI-NRS) 17 , which consists in 11 numbers, from 0 (no pain) to 10 (worst pain), over a horizontal 10-cm line.
Chronic lower back pain was evaluated using the Nordic Musculoskeletal Questionnaire (NMQ) 18 , which asked if chronic lower back pain had occurred for longer than 4 weeks in the previous 12 months. The participant also answered if the pain was associated with surfing.
Lumbar disability was investigated with the QUEBEC Back Pain Disability Scale Questionnaire 19 , and the participant evaluated how hard it is to perform 20 daily activities. The scores of the items were added up, to a total score within the range of 10 and 100, with higher numbers representing greater levels of disability.
Lumbar function was evaluated with the Back Performance Scale (BPS) 20 , which consists in conducting 5 tests to evaluate the physical performance of the lower back region in different daily life activities. The score was obtained by adding up the individual scores of each tests, with the higher scores indicating the worst performance.
Lower back flexibility was measured by Schober's test 21 , with a variation equal or greater than 5 cm being considered normal.
The range of motion of the lumbar spine was evaluated with goniometry 21 . The maximal active range of motion of the flexion and extension of the lumbar spine was requested, in degrees. A freedom of movement between 0 and 95 o was considered normal for lumbar flexion, and between 0 and 35 o for lumbar extension 21 .
The thoracic and lumbar angles were measured in degrees with a spline. Previous evidences 22 indicate that the method is strongly correlated with the gold standard test performed in radiography. The method 22 consists in the palpation and marking of the spinous processes, molding the flexible ruler of 80 cm (spline) from the seventh cervical vertebrae (C7) to the first sacral vertebrae (S1) and then drawing the form in graph paper. The angle is determined by an algorithm developed in the Matlab software with a third-degree polynomial. The measurement was done in three repetitions by a single inter-rater which presented an intra-class correlation coefficient of: ICC lumbar=0.83, p=0.003; ICC thoracic=0.82, p=0.004. Values between 20 and 60 o for the thoracic curvature and 22 and 54 o for the lumbar curvature were considered normal. Values below the reference values were considered rectifications of the curvature, and those above it, thoracic hyperkyphosis or lumbar hyperlordosis.
The statistical analysis was performed using the Statistical Package for the Social Sciences (SPSS) software, version 21.0. All the data were submitted to an analysis of normality and homogeneity of variances with the Kolmogorof-Smirnov and Levene tests, respectively. The nominal and/or ordinal variables were described in frequency and in percentage, while numerical variables were described in average and standard deviation.
To analyze the categorical dada, we used Pearson's chi-square test. For the numerical variables, ANOVA was used among the groups with Bonferroni's post-hoc test. For all the analyses, the level of significance was fixed at p<0.05. The size of the effect was determined through the calculation of the omega, with ω =0.01 being considered a small effect, ω =0.06 a moderate effect and values above 0.14 a large effect 23 .

RESULTS
Presence of lower back pain, periodicity and association with surfing Table 2 shows there was a significant association between the presence of chronic low back pain and surfing, χ 2 (1) = 5.97 (p=0.05). However, there was no statistically significant difference between the three groups of the study for the occurrence of lower back pain (acute or chronic) or for its periodicity.
Kinetic and functional aspects (intensity of the lumbar pain, disability, function, flexibility, range of motion and angle of the thoracic and lumbar spine) Table 3 presents the kinetic and functional aspects of the three different experimental groups. The effect of the number of years surfing was significant for pain intensity, F (2, 39) = 4.40, p = 0.01, ω = 0.15 (large effect size).
The analyses also revealed that the lumbar angle was greater for those who had been surfing for a period between 5 and 9.9 years, in comparison with those who had surfed for less time (up to 4.9 years), F (2, 65) = 3.38, p = 0.04, ω = 0.07 (moderate effect size). However, this difference was not confirmed in Group 3, which had the longest surfing period (p > 0.05).
As a result, to eliminate the effect of the changes caused by age, we conducted statistical analyses using age as a covariate. The results showed that age had no significant relationship with pain intensity nor with the lumbar angle, F (2, 39) = 2.49, p = 0.12, r= 0.37 (large effect size).

DISCUSSION
In this study, most young men who were eutrophic, active, who surfed recreationally three times a week, with a larger angle of the lumbar curvature and who had surfed the longest presented more intense lower back pain.
In the present study, more than half of the interviewees (60.6%) reported that at least one episode of lumbar pain had occurred in the previous 4 weeks. Similarly, 68.2% of surfers reported having lumbar pain in the previous 12 months. Steinman et al. 7 revealed the high prevalence of recurring lower back pain (28.4%) in recreational surfers from Brazil who had surfed for more than 5 years. The authors suggest that after years of surfing, due to the repetitive movements of compressing and rotating the spine, the dehydration of intervertebral disks may occur, leading to pain and even disk degeneration. Moreover, the cervical and thoracic spines may suffer injuries, causing muscle imbalance due to the isometric hyperextension during paddling and predisposing surfers to musculoligamentous injuries caused by trauma.
There is also evidence 12 that accelerating the popup (quick movement to change from paddling to standing up on the surfboard) is a probable cause for the occurrence of lower back pain and injury. This is based on the physical relationship between the acceleration and the forces of tension at work during the movement, since it is an intense and explosive movement of rotating and compressing the lumbar spine.
With the goal of identifying the prevalence of lower back pain in surfers from Rio de Janeiro, Souza et al. 8 observed that lower back pain was more common in surfers than in non-surfers. These findings corroborate the results of the present study, where we found a significant association between the presence of chronic lower back pain and surfing.
With respect to the presence of lower back pain and the years of surfing, Daniels et al. 24 state that lower back pain is a common complaint among athletes, with traumas and infections being the most frequent causes in teenagers, while for adults they are mechanical or a consequence of osteoarthritis. De Luigi 25 states that the high incidence of structural injuries and lower back pain is associated with young athletes. Contrarily, Nathanson et al. 3 affirm that older surfers (age higher than 40) and more experienced surfers (more than 20 years of surfing) have higher relative risks of injuries, with the 35-55 age bracket being the most affected by lower back pain 26 . These statements partially contradict the findings of our study, in which no significant differences were found between the three studied groups, which were subdivided according to years of surfing for acute pain, occurrence of chronic lumbar pain or its periodicity. As for pain intensity, those who had surfed the longest (Group 3) had more intense lower back pain. However, when we eliminated the effect of the changes which could be related to age, the results indicated that age does not have a significant relationship with pain intensity.
Posture changes may occur due to factors such as muscle hypertrophy, imbalance between agonist/ antagonist muscles, the decrease of flexibility due to repetitive movements and intense training for athletes 27 . Moreover, the increase of lumbar lordosis may directly cause lumbar pain, which was previously demonstrated by wrestling athletes who had chronic lumbar pain -the angle of their lumbar curvature was greater than that of asymptomatic individuals 28 , but this association has not been investigated for surfers up to the present moment. Surfers spend about 45-50% of their time on the surfboard paddling, which favors spine hyperextension 7 , which strengthens the posterior chain isometrically, possibly leading to muscle imbalance 29 . These results are compatible with the findings of the present study, in which the lumbar angle was greater for those who had surfed the longest when compared with those who had surfed less, suggesting that surfing may contribute to the increase of the lumbar curvature. However, the increase was not confirmed in Group 3, which had surfed the longest. Moreover, when we eliminate statistically the effect of changes brought by age, the results indicate that age did not have a significant relationship with the lumbar curvature and/or pain intensity.
In addition to the increase of the lumbar curvature, there are evidences that low back pain can be related to the loss of flexibility in the region 30 . Considering these indications, in our study we did not find an association between low back pain and flexibility and/or the range of motion of the lower back. Most participants (53%) presented values of normality for flexibility, but 57.5% showed loss of motion for lumbar flexion, and 36.3% showed restrictions for lumbar extension. Thus, in this study it was not possible to state that a restricted motion of the lower back leads to pain in the area.
There was also no association between lower back pain and lumbar disability, which was evaluated with the QUEBEC questionnaire, and no surfer presented a score greater than 30. This suggests that low back pain in surfers is not disabling. This finding is compatible with the evaluation of lumbar function, for which 95.5% of surfers presented a performance with no limitation (level 0) or minimally limited (level 1). In addition, the same occurred with the assessment of the thoracic curvature, for which 95.5% of the surfers presented angles considered normal. Thus, due to the indices of normality obtained in the sample of this study, the results of these variables should be interpreted with caution. Hence, future studies should analyze the relationship between lumbar disability and the loss of thoracic and lumbar curvature, and the flexibility of surfers with low back pain.
Although the present study explored the association between low back pain and kinetic and functional aspects, such as disability, function, flexibility, range of motion and the curvature of the thoracic and lumbar spines of surfers, some limitations can be mentioned so that they are studied by future researches, such as the aspect of practicing other sports in addition to surfing and specific training. Moreover, other methods can be used to collect data on low back pain instead of questionnaires and interviews.
We highlight that the clinical contribution of this work is relevant, since it shows the importance of evaluating the angle of the lumbar curvature for the choice of therapies aimed at preventing and reducing the intensity of low back pain in surfers. The data presented in this study showed some factors that cause low back pain in surfers, in particular the increase of the lumbar curvature. Hence, we single out the importance of postural re-education to correct the angle of the lumbar curvature in the prophylaxis of low back pain, as well as to control this type of pain in surfers.

CONCLUSION
There is a significant association between the occurrence of low back pain and surfing. A higher number of years of surfing seems to be associated with more intense low back pain and a larger angle of the lumbar curvature. However, for surfers low back pain is not associated with lumbar disability, function, flexibility, range of motion of the lumbar spine and the angle of the thoracic spine.