SPINE Volume 31, Number 15, pp 1740 –1744 ©2006, Lippincott Williams & Wilkins, Inc. Association Between Back Pain and Physical Fitness in Adolescents Lars Bo Andersen, PhD, Dr Med Sci,* Niels Wedderkopp, PhD,† and Charlotte Leboeuf-Yde, PhD† Study Design. A cross-sectional study of 9413 adoles- cents. Objectives. To study the associations between back pain, physical activity, and physical fitness. Summary of Background Data. A high physical fitness level, and especially muscle endurance in the back mus- cles, is associated with lower risk of back pain, but little is known about other types of physical fitness and back pain in adolescents. Methods. A cross-sectional study of 3956 boys and 5457 girls 17 years of age. The associations between self- reported back pain and different types of physical fitness and self-reported physical activity were analyzed in high schoolchildren in Denmark. Results. Back pain was reported by 43% of the girls and 37% of the boys. Back pain was associated with low isometric muscle endurance in the back extensors, and the highest quartile had a lower risk of back pain (odds ratio = 0.71; 95% confidence interval, 0.62– 0.82) within the last month. No associations were found to aerobic fitness, functional strength, flexibility, or physical activity level after adjustment for muscle endurance. More girls than boys experienced back pain, and it was more com- mon in taller adolescents. Conclusion. Children with high isometric muscle en- durance were less likely to report back pain. No other measures of physical fitness or level of self-reported physical activity were linked to back pain reporting. Key words: back pain, adolescents, physical fitness, physical activity. Spine 2006;31:1740 –1744 Back pain in children was earlier thought to be rare and, when present, it was thought to indicate serious disor- ders. 1 Later studies indicate that back pain starts early in childhood, 2–5 and a steep incline in the prevalence of low back pain (LBP) has been reported around puberty. 6,7 Whether the back pain in children develops into serious problems later in life is not known, but it is a predictor for future back problems. 8 As back pain is one of the diseases causing most days off from work in the adult population, it is both from an economically point of view and for the subjects suffering from back pain important to study preventive strategies and possible causes of back pain. Physical activity and fitness may be linked to back pain. Physical inactivity may result in diminished muscle strength or muscle endurance, reduced bone mineral content, and poor flexibility and coordination, which could all contribute to back pain. Previous studies have shown that low isometric mus- cle endurance in the back extensors assessed with the Sørensen test was associated with a risk of LBP during the next year in middle aged men and women, and causal inference has seriously been considered. 9 However, the predictive value of other physical performance measures in general is not well studied, and studies we found did not provide us with a clear picture. Jackson et al did not find an association between sit-and-reach or sit-ups and LBP in adults. 10 Oldervoll et al compared the effects of aerobic training and strength promotion exercises on back pain and found that improvement in aerobic fitness was not necessary to reduce back pain. 11 Nourbakhsh and Arab tested the association between 17 mechanical factors and LBP and found that endurance of the back extensor muscles had the highest association with LBP. 12 Spinal stabilization exercise programs can increase mus- cle endurance substantially both in healthy subjects and LBP patients, and it may therefore be possible to treat or prevent LBP if low muscle endurance at least partly causes LBP. 13 However, few studies have assessed the association between physical performance and back pain in adolescents. 14,15 The present study was conducted in Denmark to mon- itor the physical activity and fitness level of high school children. Questionnaires including physical activity hab- its and back pain were sent to all high schools in the country, and physical fitness was assessed in almost 10,000 adolescents. The aim of the present study was to examine the association between physical fitness, physi- cal activity, and self-reported back pain in adolescents. Methods The study population was 9,413 first grade high school adoles- cents, 3,956 boys and 5,457 girls, from Denmark with a mean age of 17.1 years (SD, 0.6 years). More than 12,000 answered the questionnaire, but some of these did not answer the back questions. The total high school population in this grade was 23,231, which give a participation rate close to 50%. All 150 high schools in Denmark were invited to participate, of which 107 schools participated. Participation of classes was decided by the physical education teachers from participating classes, and very few individual students from participating classes did From the *Norwegian School of Sport Sciences, Oslo, Norway; †The Back Research Center, Ringe; and the University of Southern Denmark, Denmark. Acknowledgment date: June 23, 2005. First revision date: August 23, 2005. Acceptance date: September 19, 2005. The manuscript submitted does not contain information about medical device(s)/drug(s). No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript. Address correspondence and reprint requests to Lars Bo Andersen, PhD, Dr Med Sci, Norwegian School of Sport Sciences, Postbox 4014, Ullevål stadion, Sognsveien 220, 0806 Oslo, Norway; E-mail: lars.bo.andersen@nih.no 1740