Abstract
BackgroundThe flexion relaxation phenomenon (FRP) has been widely investigated. Nevertheless, no study has been reported on the FRP as well as spasm response to large lifting load. The aim of this study was to evaluate the effect of large lifting load on the FRP response and spasm during execution of a flexion-extension exercise.MethodsTwenty-two healthy male university students without low back pain history participated this study. Subjects randomly performed three trials of trunk flexion-extension cycles of 5 s flexion and 5 s extension in each of 4 conditions (three large lifting loads of 15, 20 and 25 kg and one lifting load of 0 kg for comparison). Surface EMG from bilateral erector spinae was recorded during the performance of a trunk anterior flexion-extension exercise. The relaxation phase was determined through the onset of electromyography (EMG) signals. Spasm was evaluated in the relaxation period. The mean normalized electromyography (NEMG) was derived from the raw EMG.ResultsSpasm was observed in more than 45% of the individuals and the intensity of muscle activation was increased by more than 78% in the relaxation phase.ConclusionsA large lifting load could lead to a high prevalence of spasms as well as a high intensity of muscle activations on erector spinae muscle in the relaxation period, which may be associated with the development of low back disorder during the performance of a flexion-extension exercise.
Highlights
IntroductionNo study has been reported on the flexion relaxation phenomenon (FRP) as well as spasm response to large lifting load
The flexion relaxation phenomenon (FRP) has been widely investigated
The main results of this study showed that, during anterior trunk flexion-extension with a large lifting load, spasms occurred with a high prevalence, and the normalized normalized electromyography (NEMG) showed a significant increase in the relaxation period
Summary
No study has been reported on the FRP as well as spasm response to large lifting load. The aim of this study was to evaluate the effect of large lifting load on the FRP response and spasm during execution of a flexion-extension exercise. In a previous experimental investigation, Solomonow et al [31] found that during sustained static lumbar flexion, bilateral spasms were occasionally observed on the erector spinae (ES). After sustained static lumbar flexion, the relaxation period (from the time of the EMG-off in the flexion phase to the time of the EMG-on in the extension phase) in the FRP on the ES was found to be shorter during the execution of a trunk anterior flexion-extension. Based on the mechanism of a synergistic load sharing between passive tissues and active muscles (e.g., ES) in the FRP [8,9,10], Solomonow et al [31] pointed out that the increase of ES muscle activation would indicate the compensation for the decreased ability to resist the tension of stretching
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