Short rest periods after static lumbar flexion are a risk factor for cumulative low back disorder

https://doi.org/10.1016/j.jelekin.2004.06.005Get rights and content

Abstract

The objective of this work was to study the effect of rest periods of various durations applied between six 10-min sessions of static flexion on the development of cumulative low back disorder (CLBD). Three experimental groups of a feline model were used, and the rest duration between sequential static load periods was set to 5, 10, and 20 min, with a corresponding load-to-rest ratio of 2:1, 1:1 and 1:2, respectively. The reflex electromyographic (EMG) activity from the multifidus muscles and supraspinous ligament displacement (creep) were recorded during the flexion periods and over 7 h of rest following the load–rest cycles. It was found that a minor disorder developed in all the groups whereas a severe neuromuscular disorder including a delayed hyperexcitability was observed only in the group subjected to 5 min rest. The two-way ANOVA showed a significant effect of time post loading (p < 0.001) and rest duration (p < 0.001) on the Normalized Integrated EMG (NIEMG) recovery data; a significant effect of time post loading on the Displacement data (p < 0.001) was observed as well. The post hoc Fisher test performed on the NIEMG data during the recovery phase showed a significant difference between the group subjected to 5 min rest and the other two groups (p < 0.001). These results suggest that while a short rest period of 2:1 load-to-rest ratio leads to CLBD, longer rest at 1:1 and 1:2 load-to-rest ratio are more favorable for preventing or attenuating the development of CLBD. Short rest periods between sessions of static lumbar flexion, therefore, are a risk factor for the development of CLBD.

Introduction

Epidemiological studies point out that static lumbar flexion performed daily by workers in various professions (construction, roofing, welding, farm workers, etc.) leads over time to the development of cumulative low back disorder (CLBD) [7], [16], [22], [26]. The disorder is characterized by low back pain, weakness, limited range of motion and stiffness or spasms in the posterior muscles. It is a chronic disorder exhibiting very little improvement by various therapeutic modalities. The epidemiological data further point out that risk factors for CLBD consist of high load magnitude, longer duration over which the load was sustained, higher number of daily repetitions and frequency. Experimental biomechanical confirmation of the epidemiology available on this subject is lacking.

The feline model was used in the series of studies yielding significant new insights on the development of a neuromuscular disorder [28] and its mathematical model [28], [29], [30]. Briefly, it was demonstrated that anterior lumbar flexion at constant load strains the viscoelastic tissues (posterior ligaments, discs, facet capsule, etc.) and develops creep over time as was also confirmed with humans and the porcine model [4], [14]. Creep is associated with development of microdamage in these tissues and the consequences of spasms [9], [19], [34], [35] and acute inflammation [11], [28]. The myoelectric response to inflammation in the viscoelastic tissues was shown to be a prolonged delayed hyperexcitability of the multifidus muscles that started 2–3 h after the work was terminated and lasted 1–3 days, depending on the extent of the inflammation [28]. Overall, the description of the disorder and its inflammatory and biomechanical correlates proved useful in assessing the multifactorial aspects of CLBD.

Initial results from a systematic exploration on this subject aimed to obtain biomechanical validation of the epidemiology yielded interesting observations. Load magnitudes near the upper limits of the physiological range resulted in a severe neuromuscular disorder whereas static lumbar flexion under moderate or low loads did not [23]. Furthermore, repetition of 10-min static flexion followed by 10 min rest for three and six times did not induce a severe disorder whereas nine repetitions resulted in a severe disorder regardless of the load magnitude applied [24]. Additional findings point out that longer periods of static flexion followed by a fixed intersession rest of 10 min also resulted in a severe disorder [10] confirming that flexion duration is also a risk factor. Evidently, the duration of the rest period may also be a significant factor, and that is the subject of this investigation.

Therefore, the aim of the present study was to assess the risk of rest periods of various duration applied to the lumbar spine of feline preparations between a sequence of six periods of 10 min of static lumbar flexion, and followed by 7 h of rest. In an attempt to possibly identify an optimal work to rest ratio, three protocols were used; the rest duration between sequential 10-min static load periods was set to 5, 10, and 20 min, respectively. We hypothesize that shorter rest periods (5 min, corresponding to a 2:1 load-to-rest ratio) would elicit a more pronounced neuromuscular disorder in comparison to a 1:1 (10 min rest) or a 1:2 load-to-rest ratio (20 min rest) which might prevent or attenuate the manifestations of an acute neuromuscular disorder which may further lead to a cumulative low back disorder.

Section snippets

Preparation

21 adult cats (weight 3.81 kg ± 0.44) were used in this study. Cats were anesthetized with 60 mg/kg chloralose, according to a protocol approved by the Institutional Animal Care and Use Committee (IACUC). The skin overlying the lumbar spine was dissected to expose the lumbar fascia, and an S shaped stainless-steel hook was applied around the supraspinous ligament between L-4 and L-5. The preparation was then positioned in a rigid stainless-steel frame and fixed for subsequent EMG electrodes

Results

A typical example of the EMG and displacement behavior during two different protocols is shown in Figs. 1(a) and (b). Fig. 1(a) refers to a preparation subjected to six 10-min work sessions spaced by 5-min rest periods (6 × 10:5), while Fig. 1(b) shows the response obtained in a preparation for six 10-min work sessions spaced by 20 min rest periods (6 × 10:20). In the top three traces of each graph, the raw EMG is presented; the fourth trace represents the displacement and the bottom trace the load

Discussion

The major results obtained in this study consist of the presence of a severe acute neuromuscular disorder as a consequence of a short rest period between six sequential 10-min periods of static load application to the lumbar spine in feline preparations as opposed to a minor disorder when longer rest periods were applied. This disorder was described as the combination of different features consisting of the presence of spasms within the EMG signal, a progressive decrease in the EMG amplitude

Acknowledgments

This work was supported by the National Institute of Occupational Safety and Health with Grants OH-04079 and OH-07622. Paola Sbriccoli was a research fellow from the Department of Human Movement and Sport Sciences, University Institute of Motor Sciences (IUSM) of Rome (Italy), and Amy Courville was a graduate student in Physiology, LSUHSC. Both were supported by Grant HEF (2000-5)-7 from the Louisiana Board of Regents.

Amy Elizabeth Courville received a B.S. in Biological Sciences from Louisiana State University A&M in Baton Rouge, Louisiana. She is currently pursuing a M.S. in Physiology from Louisiana State University Health Sciences Center in New Orleans, Louisiana.

References (35)

  • M.H. Cole et al.

    Low back pain and lifting: a review of epidemiology and aetiology

    Work

    (2003)
  • L. Ekstrom et al.

    Intervertebral disc response to cyclic loading

    Proceedings of the Institution of Mechanical Engineering

    (1996)
  • E. Eversull et al.

    Neuromuscular neutral zones sensitivity to lumbar displacement rate

    Clinical Biomechanics

    (2001)
  • A. Haig et al.

    Prospective evidence for change in paraspinal muscle activity after herniated nucleus pulposus

    Spine

    (1993)
  • W.E. Hoogendoorn et al.

    Flexion and rotation of the trunk and lifting at work are risk factors for low back pain: results of a prospective cohort study

    Spine

    (2000)
  • W. Hoyt et al.

    EMG assessment of chronic low back pain syndrome

    Journal of the American Osteopathic Association

    (1981)
  • M. Jackson et al.

    Multifidus EMG and tension relaxation recovery after prolonged static lumbar flexion

    Spine

    (2001)
  • Cited by (23)

    • The effect of sustained static kneeling on kinetic and kinematic knee joint gait parameters

      2015, Applied Ergonomics
      Citation Excerpt :

      This hypothesized mechanism is supported by research showing that a constant tibial load (200 N for men and 150 N for women) for a period of 10 min, at knee flexion angles of 35 and 90°, induced ligament creep in the human ACL and associated neuromuscular disorders, as demonstrated by 3–5 mm of tibial displacement and quadriceps and hamstring muscle spasms immediately following the protocol (Chu et al., 2003). Although the duration of residual creep was not reported in the study by Chu et al. (2003), Courville et al. (2005) showed that three cycles of work-to-rest ratio of 2:1, with 10 min of static lumbar flexion in felines, resulted in signs of a neuromuscular disorder and ligament creep lasting over 7 h. Additionally, prolonged static loads on ligaments induce acute inflammatory responses that lead to acute neuromuscular disorders and the associated injury risks (as reviewed by Solomonow, 2006). Additionally, the proposed pathway connecting occupational kneeling to the onset of KOA via knee instability (Fig. 1) is supported by Sharma (2001) and Andriacchi et al. (2004), who reported that decreased joint stability, as caused by ligament laxity, proprioceptive deficits, or neuromuscular impairments, is a risk factor for KOA.

    View all citing articles on Scopus

    Amy Elizabeth Courville received a B.S. in Biological Sciences from Louisiana State University A&M in Baton Rouge, Louisiana. She is currently pursuing a M.S. in Physiology from Louisiana State University Health Sciences Center in New Orleans, Louisiana.

    Paola Sbriccoli, PhD., MD was born in 1964. In 1986 she graduated “cum laude” at the ISEF (Superior Institute of Physical Education) of Rome. In 1994 she received her Medical Doctor degree from the University of Rome “La Sapienza” and in 1998 she specialized “cum laude” in Sport Medicine. From May 2003 to April 2004 she has attended a research fellowship at the Bioengineering Laboratory (Department of Orthopaedics) of the Louisiana State University Health Sciences Center in New Orleans, Louisiana USA where she worked on neuromuscular function and dysfunction in spine and knee in humans and animal preparation. Her present appointment is at University Institute of Motor Sciences of Rome, Faculty of Motor Sciences as researcher in Methods and Teaching of Sports Activities. She is ordinary member of the Physiological Society of Italy, the European College of Sport Science, and the International Society for Electrophysiology and Kinesiology. Her main interests in research are non-invasive assessment of muscle damage and repair, and linear and non-linear analysis of sEMG signals in healthy humans.

    Bing He Zhou (M’89) graduated in 1970 from the Department of Electronic Engineering, University of Science and Technology of China (USTC) in Beijing, China.

    From 1970 to 1978, he worked as an Electronics Engineer at the Beipiao Broadcasting Station in Liaoning Province. In 1978, he joined the faculty of the Department of Electronic Engineering at USTC, where he was an Associate Professor of Electronic and Biomedical Engineering and the Vice Director of the Institute of Biomedical Engineering. From 1985 to 1987, he was a Visiting Research Professor in the Bioengineering Laboratory at Louisiana State University Medical Center (LSUMC) in New Orleans, where he worked with the laboratory staff on various studies related to the analysis and control of the neuromuscular system, electromyography, and instrumentation design. Currently, he is a Research Professor in the Bioengineering Laboratory at LSUMC. His teaching and research interests focus on analog and digital electronics, biomedical electronics, digital signal processing, and microcomputerized medical instrumentation.

    Dr. Zhou is a Committee Member of the International Union of Radio Science (USRI), the Commission of Electromagnetics in Biology and Medicine (Commission K), and the Chinese Biomedical Electronic Society. He is also a Senior Member of the Chinese Electronic Society, as well as a member of the Chinese Biomedical Engineering Society, the Chinese Computer Society, and the IEEE/Engineering in Biology and Medicine Society. He received the Zhang Zhongzhi Award for excellent teaching and research activities at USTC in 1989, and first-place awards for most outstanding academic paper from the Chinese Biomedical Electronic Society (1991) and the Anhui Biomedical Engineering Society (1992).

    Dr. Moshe Solomonow is a Professor and Director of Bioengineering and of The Occupational Medicine Research Center at Louisiana State University Health Sciences Center in New Orleans, Louisiana. He received the B.Sc., and M.Sc. in Engineering and the Ph.D. in Engineering and Neuroscience from the University of California, Los Angeles.

    He is the Founding Editor of The Journal of Electromyography and Kinesiology, and serves on the Editorial Board of several bioengineering and medical journals. Dr. Solomonow is a consultant to the National Science Foundation, National Institute of Health, Center for Disease Control, The Veterans Administration and scientific agencies of several European and Asiatic governments and Canada. He was a council member of the International Society of Electrophysiological Kinesiology, the International Society of Functional Electrical Stimulation, and the IEEE-Biomedical Engineering Society. He published over 120 refereed journal papers on motor control, Electromyography, muscle, ligament and joint Biomechanics, electrical muscle stimulation, prosthetics and orthotic systems for paraplegic locomotion, and supervised more than 150 engineering, physical therapy, medical students and orthopaedic residents, as well as postgraduate students and fellows from several countries.

    Dr. Solomonow organized the EMG Tutorial Workshop in the ISB Congress, the Canadian Society of Biomechanics, The Human Factors and Ergonomics Society, and The Society for Clinical Movement Analysis, was on the organizing committee of numerous conferences and gave keynote and symposia lectures in many others. He received the Crump Award For Excellence in Bioengineering Research (UCLA), the Distinctive Contribution Award from Delta 7 Society (France), The Doctor Medicine Honoris Causa (Vrije Universitiet, Brussels), The I. Cahen Professorship (LSUHSC) and the 1999 Volvo Award For Low Back Pain Research.

    Dr. Yun Lu received his medical degree from Xian Medical College in China in December of 1982. He was an orthopaedic resident from 1983 to 1986; chief resident from 1986 to 1987; and attending orthopedic surgeon from February 1988 to December 1988, at West Capital Hospital of the Fourth Military Medical University, Xian, China. He was a post-doctoral fellow from 1988 to 1989 at the Department of Orthopaedic Surgery, School of Medicine, Johns Hopkins University, Baltimore, MD, and a fellow in the Department of Orthopaedic Surgery at Louisiana State University in New Orleans, since 1989. He is a Research Professor in the Bioengineering Laboratory at LSUHSC.

    Dr. Evailina Burger completed her undergraduate and medical degrees from the University of the Orange Free State and from the University of Pretoria in the Republic of South Africa. She served as Captain in the Spine Unit in the South African Defense Force, Department of Orthopaedics. She then completed her internship at Vereeniging & Sebokeng Hospitals (now know as Kopanong Hospital), and her orthopaedic training at Kalafong Hospital Pretoria (University of Pretoria). She served as Senior Orthopaedic Consultant and Head of the Spinal Unit at Pretoria Academic Hospital, University of Pretoria, with special interest in the Pediatric Orthopaedic Unit and was in private practice at Pretoria East Neuro-Orthopaedic Hospital in Pretoria.

    Dr. Burger’s research interests include scoliosis, spondylolisthesis, patella and ulna fractures, intervertebral discs, and the efficacy of drugs used in orthopaedic surgery.

    She is a member of several national and international organizations, including the American Association of Orthopaedic Surgeons (International Member), the Scoliosis Research Society (International Member), the AO Alumni, the Greater New Orleans Orthopaedic Society, the South African Spine Cord Society, and the South African Spine Cord Association. Dr. Burger’s teaching responsibilities include teaching the annual spine course to undergraduate students in South Africa, Committee Member for the SAOA Instructional Course spine Symposium, Chairperson for the AO Advanced Spine Course and the Spine Symposium for General Practitioners, and the ABC Fellows Coordinator for South Africa and New Orleans. Dr. Burger serves as a reviewer of the Journal of Orthopaedics and is ATLS Trauma certified.

    Dr. Burger has been an Associate Professor and Head of the Spine Unit at LSUHSC Department of Orthopaedics since November 2001.

    View full text