Elsevier

Clinical Biomechanics

Volume 22, Issue 7, August 2007, Pages 745-757
Clinical Biomechanics

Short rest between cyclic flexion periods is a risk factor for a lumbar disorder

https://doi.org/10.1016/j.clinbiomech.2007.03.010Get rights and content

Abstract

Background

The epidemiology identifies cyclic lumbar loading as a risk factor for cumulative trauma disorder. Experimental biomechanical and physiological confirmation is lacking. The objective of this study was to asses the impact of different rest durations applied between periods of cyclic loading on the development of an acute lumbar disorder which, if continued to be subjected to loading, may develop into a cumulative disorder.

Methods

Three groups of in vivo feline preparations were subjected to six sequential 10 min loading periods of cyclic lumbar flexion at 40 N with a frequency of 0.25 Hz applied to the L-4/5 level. The rest durations varied from 5 min in the first group, to 10 min in the second and to 20 min in the third. Reflexive EMG from the multifidi and lumbar displacement were used to identify significant (P < 0.001) effects of time and rest duration for post-load EMG and displacement. Single-cycle test were performed hourly for 7 h post-loading to assess recovery. A model developed earlier was applied to represent the experimental data.

Findings

The groups allowed 5 and 10 min rest exhibited an acute neuromuscular disorder expressed by a significant (P < 0.001) delayed hyperexcitability 2–3 h into the 7 h recovery period with the intensity of the hyperexcitability significantly higher (P < 0.001) for the group allowed only 5 min rest. The group allowed 20 min rest had a slow, uneventful recovery, free of delayed hyperexcitability.

Interpretations

Occupational and sports activities requiring repetitive (cyclic) loading of the lumbar spine may be a risk factor for the development of a cumulative lumbar disorder and may require sufficient rest, as much as twice as long as the loading period, for prevention. Comparison to similar data for static lumbar loading shows that cyclic loading is more deleterious than static loading, requiring more rest to offset the negative effect of the repeated acts of stretch.

Introduction

Epidemiologic data identifies repetitive (cyclic) flexion to be a risk factor for cumulative trauma disorder (CTD) in the lumbar spine (Andersson, 1999, Bernard et al., 1997, Manchikanti, 2000, Melhorn, 2003). Up to 42% of the costs associated with worker’s compensation claims are associated with low back pain, many of which are diagnosed as idiopathic (Manchikanti, 2000). Identifying risk factors and mechanisms of injury could help lessen the large financial burden and safety issue that CTD presents in the workplace. In the case of cyclic loading, a cumulative effect is observed by the presence of creep in the viscoelastic tissues caused by microdamage to the collagen fibers present in the tissue (Williams et al., 2000). Because of the cumulative effect, even moderate loads are sufficient to cause an acute neuromuscular disorder. Microdamage to the collagen fibers elicits an acute inflammatory response in an attempt to promote healing (Solomonow et al., 2003b, Solomonow, 2004). Given inadequate rest time and further exposure to load, acute inflammation can become chronic and can lead to a debilitating, cumulative neuromuscular disorder (Fransen et al., 2002; Solomonow et al., 2004). The symptoms of CTD include pain, weakness, spasms, and decreased range of motion (Barbe et al., 2003, Bernard et al., 1997, Fryer et al., 2004, Kang et al., 2002, Halbertsma et al., 2001). More insight is needed to understand the mechanisms and risk factors of CTD so as to prevent and treat the disorder more effectively.

Previous work with a feline model using static flexion has identified load magnitude (Sbriccoli et al., 2004a, Sbriccoli et al., 2004b), load duration (LaBry et al., 2004), number of repetitions (Sbriccoli et al., 2004a, Sbriccoli et al., 2004b), short rest periods (Courville et al., 2005), and work to rest ratios (Sbriccoli et al., 2006) to be risk factors in the development of an acute neuromuscular disorder. This disorder was manifested by EMG spasms and decreased EMG during the loading periods and by initial and delayed hyperexcitability during the rest period. Recent studies with cyclic flexion have examined the effect of load frequency (Lu et al., 2004), load magnitude (Claude et al., 2003), and number of repetitions (Navar et al., 2006) on a feline model. Furthermore, cyclic flexion has been shown to have a more harmful effect than static flexion for similar protocols investigating loading repetitions and load magnitude. Further exploration into the effect of rest durations on cyclic flexion and its relative effect to static flexion is needed and that is the focus of this study.

The objective is to investigate the effect of short rest durations on cyclic loading in order to provide biomechanical and physiological evidence to support and validate previous epidemiological findings. In a previous static loading study examining the effect of rest periods it was found that work to rest ratios of 1:1 or lower prevented the development of an acute neuromuscular disorder (Courville et al., 2005). We hypothesize that short rest durations between cyclic loading periods will cause an acute neuromuscular disorder. Also, we predict that cyclic loading will elicit a more intense neuromuscular disorder than static loading for identical load magnitudes, load durations and rest durations. Specifically, a work to rest ratio of 1:1 with cyclic flexion may not allow enough rest to prevent the development of an acute neuromuscular disorder.

Section snippets

Preparation

Twenty-one adult cats weighing 3.53 kg ± 0.34 were used in this study. Cats were anesthetized intravenously with 60 mg/kg chloralose with the pre-anesthetic intramuscular injection of xylazine, 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

Results

Fig. 1a, Fig. 1b depicts a typical response of one preparation subjected to six 10-min working periods separated by 5-min rest periods. The top three traces depict the raw EMG signal from electrodes placed between L-3/4, L-4/5, L-5/6, respectively, the fourth trace shows the displacement and the bottom trace the applied load. The EMG amplitude decreases over time during the working periods, and random spasms are present throughout. Creep is evident in the displacement traces and accumulates

Discussion

The major outcomes of this study show that short rest between periods of cyclic loading elicits an acute neuromuscular disorder. While a neuromuscular disorder is not present in the group subjected to 20-min rest, an acute neuromuscular disorder is present in the groups subjected to 10-min rest and 5-min rest. Furthermore, the intensity of the acute neuromuscular disorder increased with shorter rest periods. Caused by the accumulation of creep and microdamage to the soft tissues in the lumbar

Acknowledgement

This work was supported by Grant R01-OH-007622 from the National Institute of Occupational Safety and Health.

References (38)

  • M.W. Olson et al.

    Flexion–relaxation response to cyclic lumbar flexion

    Clinical Biomechanics

    (2004)
  • M.W. Olson et al.

    Flexion–relaxation response to gravity

    Journal of Biomechanics

    (2006)
  • R.J. Parkinson et al.

    The time-varying response of the in vivo lumber spine to dynamic repetitive flexion

    Clinical Biomechanics

    (2004)
  • S. Petrie et al.

    Mechanoreceptors in the human elbow ligaments

    Journal of Hand Surgery – American

    (1998)
  • M. Solomonow

    Ligaments: a source of work-related musculoskeletal disorders

    Journal of Electromyography and Kinesiology

    (2004)
  • M. Solomonow et al.

    Flexion–relaxation response to static lumbar flexion in males and females

    Clinical Biomechanics

    (2003)
  • M. Stubbs et al.

    The ligamento-muscular protective reflex in the lumbar spine of the feline

    Journal of Electromyography and Kinesiology

    (1998)
  • J.H. van Dieën et al.

    Trunk muscle activation in low-back pain patients, an analysis of the literature

    Journal of Electromyography and Kinesiology

    (2003)
  • Bernard, B.P. et al., 1997. Musculoskeletal disorders and workplace factors: A critical review of Epidemiological...
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