title: [Experimental simulated study on the break for manual lifting task by surface electromyography and electrocardiogram].
abstract: OBJECTIVE
  To investigate the recovery duration of manual lifting tasks.
  
  
  METHODS
  30 college student volunteers with gender equally distributed were involved in the simulated stoop-, squart- and semi squart-lifting tasks in the laboratory. Signals of electromyography (EMG) at the back muscles (left and right thorax m. erector spinae, LT(10) and RT(10); left and right lumbar m. erector spinae, LL(3) and RL(3)) and electrocardiography (ECG) were recorded during the rest intervals. The percentage of maximum voluntary electrical activation (MVE%), EMG median frequency (MF), and heart rate (HR) were analyzed to predict the recovery time required.
  
  
  RESULTS
  During the break, MVE% at 4 back muscles of all the male subjects were recovered to resting level within 5 minutes and 91.8% were within 2 minutes. Except for RL(3) after squat- and stoop-lifting task, the MVE% of female subjects went back to resting level within 3 minutes and 67.8% were within 2 minutes. The MF of male subjects were recovered in 10 minutes and 74.9% within 2 minutes, with the exception of RL(3) after stoop- and squat-lifting tasks. All the female MF were recovered in 8 minutes and 83.4% were within 2 minutes. However, during the last 20 minute break after the lifting tasks, the MVE% and MF of all male and female subjects were recovered, while HR came back to resting level within 14 and 5 minutes, respectively.
  
  
  CONCLUSIONS
  For the three manual lifting tasks with 25% MVC workload lasting for 4.5 min, a break of 15 minutes is sufficient for most erectors spinae to recover from local muscle load. However, in terms of the HR, a break of 15 minutes is enough for the recovery of systematic load.
authors.affiliation: MOE Key Lab of Environmental and Occupational Health, Department of Occupational and Environmental Health, School of Public Health, Tongji Medical College, Huazhong University of Science & Technology, Wuhan 430030, China.
authors.forename: Zheng-lun
authors.initials: ZL
authors.lastname: Wang
authors.forename: Lei
authors.initials: L
authors.lastname: Wu
authors.forename: Ting-bo
authors.initials: TB
authors.lastname: Song
authors.forename: Biao
authors.initials: B
authors.lastname: Chen
authors.forename: Li-hua
authors.initials: LH
authors.lastname: He
authors.forename: Sheng
authors.initials: S
authors.lastname: Wang
authors.forename: Lei
authors.initials: L
authors.lastname: Yang
mesh_terms: D000328:Adult; D001415:Back; D004562:Electrocardiography; D004576:Electromyography; D005260:Female; D006801:Humans; D017770:Lifting; D008161:Lumbosacral Region; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D011187:Posture; D012146:Rest / Q000502:physiology*; D016474:Weight-Bearing; D055815:Young Adult