Original article Trunk muscle response to various protocols of lumbar traction Jacek Cholewicki a, b, c, * , Angela S. Lee a , N. Peter Reeves a, b , Elizabeth A. Calle b a Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, 333 Cedar St., New Haven, CT 06520-8071, USA b Department of Biomedical Engineering, Yale University, New Haven, CT 06520, USA c Michigan State University Center for Orthopedic Research, Ingham Regional Orthopedic Hospital, 2727 S. Pennsylvania Avenue, Lansing, MI 48910, USA article info Article history: Received 3 October 2007 Received in revised form 21 July 2008 Accepted 3 August 2008 Keywords: Spinal loads EMG Flexibility abstract The purpose of this study was to compare trunk muscle activity, spinal decompression force, and trunk flexibility resulting from various protocols of spinal traction. Four experiments explored the effects of (1) sinusoidal, triangular, square, and continuous distraction-force waveforms, (2) 0, 10, 20, and 30 degrees of pull angle, (3) superimposed low, medium and high frequency force oscillations, and (4) sham traction. Nineteen healthy subjects volunteered for this study. Surface EMG was recorded during traction and later used in a biomechanical model to estimate spine decompression force. Trunk flexibility was measured before and after each treatment. There were no differences in muscle activity between any of the experimental conditions except the thoracic erector spinae muscle, which had lower EMG during continuous compared to sinusoidal distraction-force waveform (p ¼ 0.02). Thoracic and lumbar erector spinae muscles were significantly less active during sham than real traction (p ¼ 0.01 and p ¼ 0.04, respectively). The estimated L4–L5 spine compression force was 25 N. Trunk flexibility decreased after each experimental session (p ¼ 0.01), and there were no differences between sessions. Our results suggest that the trunk muscle activity is minimal and point toward fluid exchange in the disc as one of the key biomechanical effects of spinal traction. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction With low back pain (LBP) remaining one of the most prevalent and costly health problems in Western Society (Andersson, 1999), the search continues for an effective treatment. Because spinal surgery is expensive and not always effective, the management of LBP begins usually with a conservative approach. One such conservative approach is mechanical spinal traction. This type of treatment relies on the application of a continuous or intermittent distraction-force between the pelvis and ribcage. Over 30% of physical therapists surveyed in Ontario, Canada, used spinal trac- tion as the preferred treatment for subacute LBP and acute LBP with sciatica (Li and Bombardier, 2001), which represents the trends in North America. Similarly, lumbar traction is frequently used in the UK despite numerous recommendations suggesting it is ineffective (Harte et al., 2003). These recommendations, based on compre- hensive reviews of randomized clinical trials, state that lumbar traction cannot be recommended as a single therapy for LBP with or without sciatica (Harte et al., 2003; Airaksinen et al., 2006; van Tulder et al., 2006a,b; Clarke et al., 2007). However, these reviews also state that the literature does not allow for a firm negative conclusion to be made due to the small number of high quality studies published. Most of the studies had too few subjects, mixed patient population, and other methodological flaws. The exact mechanism through which traction might be effective is not known. It has been suggested that spinal elongation, by increasing intervertebral space, inhibits nociceptive nerve activity, improves mobility, reduces muscle spasm, relieves nerve root compression, and lessens adhesions around the facet joints. None of these mechanisms have been supported sufficiently by empirical data (van der Heijden et al., 1995; Clarke et al., 2007). However, all of these possible mechanisms depend on adequate distraction- force being transmitted directly to lumbar segments. During trac- tion, muscle tension and friction between the body and the support surface should be taken into account in the form of counterforces (van der Heijden et al., 1995). While the counteractive friction force can be eliminated with various technological solutions, such as a split and sliding table, the effects of trunk muscle response to lumbar traction are unknown (van der Heijden et al., 1995; Krause et al., 2000; Clarke et al., 2007). Two previous studies looked only at EMG of sacrospinalis muscles (Hood et al., 1981; Letchuman and Deusinger, 1993). Thus, relaxation of spinal muscles appears to be * Corresponding author. Michigan State University Center for Orthopedic Research, Ingham Regional Orthopedic Hospital, 2727 S. Pennsylvania Avenue, Lansing, MI 48910, USA. Tel. þ1 517 975 3302; fax: þ1 517 975 3305. E-mail address: cholewic@msu.edu (J. Cholewicki). Contents lists available at ScienceDirect Manual Therapy journal homepage: www.elsevier.com/locate/math ARTICLE IN PRESS 1356-689X/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.math.2008.08.005 Manual Therapy xxx (2008) 1–5 Please cite this article in press as: Cholewicki J et al., Trunk muscle response to various protocols of lumbar traction, Manual Therapy (2008), doi:10.1016/j.math.2008.08.005