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Lumbar Posture—Should It, and Can It, Be Modified? A Study of Passive Tissue Stiffness and Lumbar Position During Activities of Daily Living

JP Scannell, PT, MSc, is a doctoral candidate at the University of Waterloo, Waterloo, Ontario, Canada
SM McGill, PhD, is Professor of Spine Biomechanics, Faculty of Applied Health Sciences, Department of Kinesiology, University of Waterloo, 200 University Ave W, Waterloo, Ontario, Canada N2L 3G1 (mcgill{at}healthy.uwaterloo.ca).

Address all correspondence to Dr McGill

Background and Purpose. Physical therapists commonly attempt to reduce and prevent low back pain by "improving" individuals' lumbar posture. To investigate the physical therapy clinical practice of attempting to "improve" lumbar posture, measures of passive tissue stiffness and angular deformation during activities of daily living were used. Participants. The lumbar spine posture of 150 university students was measured as the inclinometer angle difference between L1 and S1. Eighteen female participants (6 with hypolordosis, 6 with hyperlordosis, and 6 controls without lumbar spine impairment) were recruited from this lumbar posture database. Hypolordosis and hyperlordosis were clinically classified by physical therapists. Methods. Lumbar passive tissue stiffness was measured during sitting, standing, and walking before and after a 12-week exercise program, and estimates of lumbar passive tissue strain were calculated from those measurements. Results. The neutral zone (NZ), a range of lumbar positions of low passive tissue stiffness, was identified. Prior to training, the subjects with hypolordosis had more passive tissue strain during sitting than the subjects with hyperlordosis, and the subjects with hyperlordosis stood in extension relative to their NZs while the control subjects and subjects with hypolordosis stood within their NZs. Before and after training, subjects in all 3 groups walked with lumbar spine positions within their NZs. After training, the lumbar posture of the subjects with hypolordosis and the subjects with hyperlordosis changed toward a "mean" (mid-range) lumbar posture. After the exercise program, subjects in all 3 groups stood and walked with their lumbar spines in positions within their NZs, and they sat with their lumbar spines flexed relative to their NZs. Discussion and Conclusion. Knowing that tissue failure can be related to passive tissue strain, the results of this study support the clinical practice of attempting to change individuals' posture-related lumbar spine positions during activities of daily living. Lumbar passive tissue strain, as estimated from the NZ and angular deformation during activities of daily living, can be decreased, but can also be increased, by an exercise program.

Key Words: Lumbar elastic equilibrium • Passive tissue strain • Posture