Low Back Pain among Medical Students in Belgrade (Serbia): A Cross-Sectional Study

Aim To examine the prevalence of low back pain, to identify self-perceived triggers of low back pain, and to investigate the impact of perceived pain on the daily activities and mood among medical students. Methods This cross-sectional study enrolled 459 fourth year students at the Faculty of Medicine in Belgrade during December 2014. The anonymous questionnaire was used for data collection. In data analysis, the chi-square test and t-test were used. Results The lifetime prevalence of low back pain was 75.8%, 12-month prevalence 59.5%, and point prevalence 17.2%. Chronic low back pain was experienced by 12.4% of the students. Both the lifetime (p=0.001) and the 12-month (p=0.001) low back pain prevalence rates were significantly higher among female medical students. Mental stress during an exam period (p=0.001), sitting at the university (p=0.002), fatigue (p=0.043), improper body posture (p=0.005), and lack of exercise (p=0.001) as self-perceived triggers of low back pain were significantly more often reported by female students, compared to males. Regarding daily functioning, the experience of low back pain mostly affects students sleeping (14.6%) and walking (12.0%). Conclusions The prevalence of LBP is high among Belgrade medical students and significantly affects their everyday functioning.


Introduction
Low back pain (LBP) is one of the most common health problems and a ects people of all ages, from children to the elderly [1,2]. According to the Global Burden of Disease 2010 Study, the prevalence and burden of LBP are very high throughout the world [3]. Out of the 291 conditions studied, LBP was found to have the sixth highest burden and to cause more disability globally than any other condition [3]. In 2010, the age-standardized point prevalence was highest in Western Europe (15%) and North Africa/Middle East (14.8%). e age-standardized point prevalence in Central Europe, including Serbia, was 11.5% (12.6% in males and 10.3% in females) and ranked the fth place [3]. However, it is estimated that over 80% of the population will experience an episode of LBP at some time during life, and that about 18% of the population experience LBP at any given moment [4]. e main risk factors for LBP are age, gender, obesity, psychosocial factors (stress, anxiety, and depression), level of education, occupational factors, decreased exibility and mobility of muscles, hypermobility, competition sports, type and way of carrying and transporting weight, postural habits, level of physical activity, smoking, and domestic factors such as watching TV and computer/videogame [5,6]. LBP often begins in childhood, and the prevalence rate for adolescents approaches that seen in adults [7]. Epidemiological studies have shown an increase in LBP in children, teenagers, and young adults [8], but studies exhibit great variability in prevalence rates [7]. It is challenging to compare the prevalence of LBP between populations and over time due to methodological heterogeneity across studies such as the age of the sample, the sample size, the de nition of LBP, the LBP recall period, the strategy for extracting data, the methodology used, and diculties in obtaining true population estimates [6,7]. Some studies reported a high prevalence of LBP among medical students [9][10][11]. Due to highly demanding curriculum during the studies, medical students are exposed to stress, sedentary lifestyle, and long hours on hospital wards and clinics which may lead to the high prevalence of LBP in this population. Also, the presence of LBP can a ect medical students' productivity, their attendance at lectures and medical training, and therefore their future career. Higher prevalence of LBP was observed among students with ve or more semesters, suggesting that advanced students who most often are exposed to practical activities are at increased risk for disease [12]. e aims of this study were to examine the prevalence of LBP (lifetime, 12-month, and point prevalence) among Belgrade clinical medical students, to identify self-perceived triggers of LBP, and to investigate the impact of perceived pain on their daily activities and mood.

Study Participants.
A cross-sectional study was conducted in December 2014 among fourth year students at the Faculty of Medicine in Belgrade. e study was approved by Institutional Review Board of the Faculty of Medicine, University of Belgrade. Students were recruited before the start of compulsory practical sessions at the Institute of Epidemiology. e purpose of the study and questionnaire's content were described to the students. A total 459 of all 533 fourth year medical students completed the questionnaire fully (response rate was 86.12%).

Questionnaire.
Each student had to ll out an anonymous questionnaire that included questions regarding the following: demographic characteristics (age, gender, and place of living), the prevalence of LBP (lifetime, 12-month, and point prevalence) and chronic LBP, self-perceived triggers of LBP (stress at the university during the exam period, sitting at the university, uncomfortable mattress, and improper body posture), the impact of pain on daily functioning (sleeping, walking, and everyday activities), and the impact of pain on mood (anger and anxiety). In order to assess self-perceived triggers of LBP and the impact of pain on daily functioning and mood, a numerical rating scale was used ranging from zero (no impact) to six (extremely strong impact). To facilitate data analysis, we collapsed responses to no impact, small/moderate impact, and strong/extremely strong impact. For students, LBP was de ned as pain in the area between the inferior margin of the 12th rib and inferior gluteal folds [3,13]. e lifetime prevalence was estimated as the proportion of respondents who had ever su ered LBP at some point in their lives. e 12-month prevalence referred to the presence of LBP in the last year, and the point prevalence referred to the presence of LBP at the moment of lling out the questionnaire (currently). We classi ed LBP as chronic if it was present for more than 12 weeks.

Statistical Analysis.
Statistical di erences between male and female students were tested using the chi-square test and t-test. A p value of <0.05 was considered statistically signi cant.

Prevalence of Low Back Pain.
e mean age of study participants was 22.46 years (SD ± 0.95), and two-thirds (66.0%) were female students. Out of 459 investigated students, 75.8% reported LBP at some point in their lives, 59.5% in the last 12 months, and 17.2% of them were suffering from LBP at the moment they were surveyed (Table 1). Chronic LBP reported 12.4% of the students. e lifetime and 12-month prevalence of LBP were signi cantly higher among female than male medical students, while the point prevalence was similar in both groups.

Self-Perceived Subjective Triggers of LBP.
e most often cited self-perceived subjective triggers with strong/extremely  (Figure 1). Other reported triggers were bad mattress, house cleaning, intensive sport activities, and weather conditions. Statistically signi cant gender di erence regarding selfperceived subjective triggers of LBP was found for mental stress during an exam period, sitting at the university, fatigue, lack of exercise, and improper body posture which were reported more often by female students (Table 2).

3.3.
e Impact of LBP on Everyday Functioning and Mood. Regarding everyday functioning, LBP mostly a ects students sleeping (14.6%) and walking (12.0%) (Figure 2), while personal interrelationships are less likely a ected by the presence of LBP. Similar ndings were observed for the presence of LBP currently and in the previous 12 months. e most medical students cited that the presence of LBP currently and in the last year annoys them and makes them angry and worry (Figure 3).

Discussion
According to the results of our study, the point prevalence of LBP among Belgrade medical students was 17.2%, 12-month prevalence 59.5%, and lifetime prevalence 75.8%. ese ndings are consistent with other studies, indicating that the point prevalence is less than the period prevalence and both are less than the lifetime prevalence [1,7,14]. e 12-month prevalence of LBP was 47.5% among students in India [9], 46.1% among Malaysian students [10], and 53.4% among Austrian medical students [15]. In a Brazilian study, which included medical and physiotherapy students, the lifetime prevalence of LBP only among medical students was 73.4%, 12-month prevalence 59.9%, and point prevalence 9.2%, while physiotherapy students reported a higher prevalence of LBP when compared with the medical students in all measures [12]. e lifetime and 12-month prevalence of LBP observed in our study were similar to those of the Brazilian study, but the point prevalence of LBP in our study was signi cantly higher than that in the Brazilian study. Higher point prevalence in our study may be explained by the fact that, in our study, fourth year medical students who were on clinical training participated and higher prevalence of LBP was observed   Pain Research and Management among older medical students, who are exposed to practical activities as mentioned earlier. In the Brazilian study, more than half of the medical students (51.2%) were preclinical, until the fourth semester. e Chinese study, conducted among fourth year medical students, as in our study, revealed a 12-month LBP prevalence of 40.1% and a point prevalence of 17.9% [11]. Female medical students in our study reported signicantly higher 12-month and lifetime prevalence, compared to male students, while the point prevalence of LBP was similar in both genders; in fact, the rate was lower in female students. According to studies conducted among children and adolescents, girls have higher prevalence rates of LBP than boys [16,17]; therefore, the lifetime LBP prevalence is expected to be higher in female students. Regarding studies conducted among medical students, most of the studies did not nd the signi cant di erence in the 12-month LBP prevalence between genders including the Chinese study [11], the study from India [9], and the Malaysian study as well, which investigated the prevalence of musculoskeletal pain including LBP too [10].
e Brazilian study compared the prevalence of LBP among medical and physiotherapy students, and the Austrian study compared the prevalence of LBP among the medical students and random sample of physical education students, and therefore they were not focused on the gender di erence of LBP among medical students. In contrast, the Australian study found that female medical students, compared to males, 1.8 times more often reported LBP [18]. e most often cited self-perceived subjective triggers with strong/extremely strong impact on LBP occurrence in our study were improper body posture, lack of exercise, and fatigue.
e study conducted among medical students in India [9] also showed that abnormal body posture was one of the factors independently associated with LBP. Although lack of exercise was reported as a risk factor for LBP in some studies [19,20], there is still con icting evidence on the potential association between physical activity and low back pain in both general population and school children [21]. Fatigue is a common complaint among medical students, and the study of Tanaka et al. [22] found that stress and coping styles were associated with severe fatigue in medical students. Medical students in our study reported fatigue as the third most often trigger of LBP.
However, female medical students, in comparison with male students, signi cantly more often reported mental stress during an exam period, sitting at the university, fatigue, lack of exercise, and improper body posture as potential triggers for LBP. In addition, the 12-month prevalence of LBP was signi cantly higher among female students. Taking into account that LBP is a multidimensional disorder, with physical, lifestyle, and psychosocial factors related to its development and maintenance [23], a possible explanation for these ndings includes that female students, in comparison with males, are more emotionally sensitive and feel fatigued more easily [24]. Also, females have greater sensitivity to painful stimuli and lower pain thresholds compared to males [25]. e study conducted among Australian adolescents indicates that being female and sitting posture are related factors for LBP, and that greater proportion of female participants than male participants were complaining of back pain that was made worse by sitting [23], which is very similar to the results of our study. e sex relationship with posture may be related to sex di erences in the shape of the pelvis, greater back muscle endurance in women, sex-speci c motor activation patterns, inappropriate furniture at the university and hospitals, behavioral issues, and other social factors such as anxiety and depression [23].
Numerous studies showed that multiple domains of psychosocial functioning are a ected by LBP experience such as social relationships, self-esteem, mood and a ect, social roles, family duties, life satisfaction, and independence in satisfying one's own needs [26]. In our study among medical students, LBP mostly a ects their sleeping quality and walking.
e study conducted at four universities in Poland indicates that LBP interferes with or limits daily activities of the students, such as sitting, standing,   or physical activity [27], and according to this study, LBP in uences sleeping in 17.7% of participants and walking in 12.8% which is very similar to the results of our study. Also, LBP experience a ects medical students' mood, and most of them make worry. erefore, it is necessary to organize physical education classes at least three times a week or daily at the faculty, as well as educational programs that theaches practical information about body mechanics and how to protect the back.
Our study has several limitations. e study participants were fourth year medical students on clinical training, and therefore, it was not possible to make a comparison among students of all six study years. Also, the survey has been undertaken in only one institution and should be expanded to include medical students from other universities in the country. Data about the experience of LBP, potential triggers, and impact of pain on daily functioning and mood were based on self-reports, and information bias is probably present. We did not collect data about BMI, smoking habits, and physical activity which future research should take into account.

Conclusions
e prevalence of LBP is high among Belgrade medical students and signi cantly a ects their everyday functioning and mood. Female students have signi cantly higher 12-month and lifetime prevalence of LBP, compared to males.

Conflicts of Interest
e authors declare that they have no con icts of interest.