title: Methods of Muscle Activation Onset Timing Recorded During Spinal Manipulation.
abstract: The purpose of this study was to determine electromyographic threshold parameters that most reliably characterize the muscular response to spinal manipulation and compare 2 methods that detect muscle activity onset delay: the double-threshold method and cross-correlation method.
  
  
  
  Surface and indwelling electromyography were recorded during lumbar side-lying manipulations in 17 asymptomatic participants. Muscle activity onset delays in relation to the thrusting force were compared across methods and muscles using a generalized linear model.
  
  
  
  The threshold combinations that resulted in the lowest Detection Failures were the "8 SD-0 milliseconds" threshold (Detection Failures = 8) and the "8 SD-10 milliseconds" threshold (Detection Failures = 9). The average muscle activity onset delay for the double-threshold method across all participants was 149 ± 152 milliseconds for the multifidus and 252 ± 204 milliseconds for the erector spinae. The average onset delay for the cross-correlation method was 26 ± 101 for the multifidus and 67 ± 116 for the erector spinae. There were no statistical interactions, and a main effect of method demonstrated that the delays were higher when using the double-threshold method compared with cross-correlation.
  
  
  
  The threshold parameters that best characterized activity onset delays were an 8-SD amplitude and a 10-millisecond duration threshold. The double-threshold method correlated well with visual supervision of muscle activity. The cross-correlation method provides several advantages in signal processing; however, supervision was required for some results, negating this advantage. These results help standardize methods when recording neuromuscular responses of spinal manipulation and improve comparisons within and across investigations.
authors.affiliation: Graduate Research Assistant, Department of Mechanical and Materials Engineering, University of Denver, Denver, CO.
authors.forename: Stuart J
authors.initials: SJ
authors.lastname: Currie
authors.affiliation: Graduate Research Assistant, Department of Mechanical and Materials Engineering, University of Denver, Denver, CO.
authors.forename: Casey A
authors.initials: CA
authors.lastname: Myers
authors.affiliation: Assistant Professor, Department of Mathematics, Physics and Engineering, Mount Royal University, Calgary, AB, Canada.
authors.forename: Ashok
authors.initials: A
authors.lastname: Krishnamurthy
authors.affiliation: Clinician, University of Colorado Hospital, Integrative Medicine Program at University of Colorado Hospital, University of Colorado Denver School of Medicine, Aurora, CO.
authors.forename: Brian A
authors.initials: BA
authors.lastname: Enebo
authors.affiliation: Assistant Professor, Department of Mechanical and Materials Engineering, University of Denver, Denver, CO. Electronic address: Bradley.davidson@du.edu.
authors.forename: Bradley S
authors.initials: BS
authors.lastname: Davidson
mesh_terms: D000293:Adolescent; D000328:Adult; D064131:Back Muscles / Q000502:physiology*; D001696:Biomechanical Phenomena; D004576:Electromyography / Q000379:methods*; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000502:physiology; D008297:Male; D020393:Manipulation, Spinal; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology*; D012018:Reflex / Q000502:physiology*; D013997:Time Factors; D055815:Young Adult
keywords: Biomechanical Phenomena; Chiropractic; Electromyography; Kinetics; Manipulation; Reflex; Spinal