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Synopsis: Greater cumulative athletic training time correlated with greater degrees of thoracic kyphosis and lumbar lordosis.
Source: Wojtys EM, et al. The association between athletic training time and the sagittal curvature of the immature spine. Am J Sports Med 2000;28(4):490-498.
This study from the university of Michigan’s Medsport and the departments of mechanical engineering, biomedical engineering, and kinesiology, as well as the Institute of Gerontology, was inspired by the chairman of the University of Michigan’s Section of Orthopaedic Surgery, Dr. Robert Hensinger. Dr. Hensinger, observing his own patient population, felt that there seemed to be an increase in thoracic kyphosis in competitive swimmers and wondered if athletic participation could be associated with a greater tendency toward saggital spinal curvature. It is known that not only can compressive loading of the spine affect vertebral apophyseal development and hence vertebral shape (as seen in Scheuermann’s kyphosis), but also mechanical loading can affect disk shape and hence spinal curvature. Furthermore, intense athletic training can, depending on the sport, result in repetitive high muscle forces about the spine that ultimately can cause significant compressive, shear, and bending loads on the vertebral endplates. Hence, Wojtys and colleagues formulated two related null hypotheses for their study. First, large angles of thoracic kyphosis or lumbar lordosis are not associated with increased exposure to athletic training, as quantified by the number of annual training hours. And second, that these angles would not differ by age, sex, or primary sport.
Two thousand two hundred and seventy children (407 girls and 1863 boys) between 8-18 years of age were enrolled in the study. Inclusion criteria for the athletic group required self reported participation in regular extracurricular athletic training and competitive sport a minimum of four days a week, three months out of the year. Youngsters in the control group denied any participation in competitive sport or physical training programs. The medial sagittal curves in the study population were measured in the upright standing position using an optical rasterstereographic method. The degree of curve was correlated with age and sex of the child and the sport in which he or she participated.
No significant differences were found between the measured sagittal angle of the thoracic and lumbar spine and the age or sex of the study population. However, both thoracic and lumbar angles of curvature increased with the number of annual training hours. The increase in curvature of the thoracic spine was proportional to training time, but the increase in curvature of the lumbar spine remaining fairly constant per training time under 400 hours per year. Additionally, curves appeared to vary according to the child’s primary sport. Curves were lowest in the sedentary controls. Those children participating in football, gymnastics, hockey, swimming, and wrestling had significantly greater thoracic and lumbar curves than those participating in track and volleyball.
This study is another well-organized and executed study from the Michigan group. It reminds us that, although moderate physical activity has a positive effect on bone development, excessive forces placed on immature bone (and in this particular case, intervertebral disks) may be detrimental. Wojtys et al enumerate the limitations of their study, which include a nonrandomized sampling technique, a "self-reported" time of athletic participation, and lack of objective measure of the magnitude of the spine loads involved. While not using conventional radiographs for quantifying the degree of thoracic kyphosis and lumbar lordosis, Wojtys et al do cite literature in which their technique for curve measurement was found to correlate with radiographic measurements with a correlation coefficient of 0.7.