title: Short rest periods after static lumbar flexion are a risk factor for cumulative low back disorder.
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.
authors.affiliation: Department of Orthopaedic Surgery, Bioengineering Laboratory, Occupational Medicine Research Center, Louisiana State University Health Sciences Center, New Orleans, LA 70112, USA.
authors.forename: Amy
authors.initials: A
authors.lastname: Courville
authors.forename: Paola
authors.initials: P
authors.lastname: Sbriccoli
authors.forename: Bing-He
authors.initials: BH
authors.lastname: Zhou
authors.forename: Moshe
authors.initials: M
authors.lastname: Solomonow
authors.forename: Yun
authors.initials: Y
authors.lastname: Lu
authors.forename: Evalina L
authors.initials: EL
authors.lastname: Burger
mesh_terms: D000818:Animals; D002415:Cats; D004576:Electromyography; D017116:Low Back Pain / Q000209:etiology / Q000503:physiopathology*; D008159:Lumbar Vertebrae / Q000502:physiology*; D023421:Models, Animal; D009119:Muscle Contraction / Q000502:physiology*; D009126:Muscle Relaxation / Q000502:physiology*; D018482:Muscle, Skeletal / Q000503:physiopathology*; D020127:Recovery of Function / Q000502:physiology; D012307:Risk Factors; D016474:Weight-Bearing / Q000502:physiology