Assessment of short-term physical loading of the back: Is serum keratan sulfate an appropriate biomarker?

Study Design: A prospective experimental study. Objectives: To investigate the potential of serum keratan sulfate (KS) as a n indicator of biochemical changes in intervertebral discs induced by physi cal loading of the back. Background: By providing objective information on exposure and effects at t he tissue level, biomarkers may enable us to improve our understanding of t he intermediate steps between exposure to physical loading and the occurren ce of back disorders. Serum KS has been proposed as a potential biomarker o f the molecular changes in intervertebral discs that occur because of physi cal loading and are a potential cause of back disorders. Methods and Measures: Thirty-two nonimpaired men volunteers with a mean age of 22.5 +/- 2.3 years participated in the experimental condition, a manual lifting task, as well as in the control condition, lying on the back. Seru m KS levels were measured immediately before and after both conditions, as well as 24 hours and 1 week later. Results: No significant changes in serum KS levels were found after exposur e to physical loading (mean +/- SD serum KS before, 287.4 +/- 83.9 ng/mL; i mmediately after, 279.5 +/- 65.5 ng/mL; 24 hours after, 266.6 +/- 71.9 ng/m L; and 1 week after, 268.9 +/- 79.3 ng/mL), and no significant changes were found after lying on the back for 8 hours (mean SD serum KS before, 273.0 +/- 94.3 ng/mL; immediately after, 261.6 +/- 68.9 ng/mL; 24 hours after, 27 7.3 +/- 68.9 ng/mL; and 1 week after, 274.5 +/- 68.5 ng/mL). Conclusions: These results indicate that the serum KS level is not suitable as a biomarker of the effects of short-term physical loading of the back i nduced by a manual lifting task.