title: Evaluation of central and peripheral fatigue in the quadriceps using fractal dimension and conduction velocity in young females.
abstract: OBJECTIVE
  Over the past decade, linear and non-linear surface electromyography descriptors for central and peripheral components of fatigue have been developed. In the current study, we tested fractal dimension (FD) and conduction velocity (CV) as myoelectric descriptors of central and peripheral fatigue, respectively. To this aim, we analyzed FD and CV slopes during sustained fatiguing contractions of the quadriceps femoris in healthy humans.
  
  
  METHODS
  A total of 29 recreationally active women (mean age±standard deviation: 24±4 years) and two female elite athletes (one power athlete, age 24 and one endurance athlete, age 30 years) performed two knee extensions: (1) at 20% maximal voluntary contraction (MVC) for 30 s, and (2) at 60% MVC held until exhaustion. Surface EMG signals were detected from the vastus lateralis and vastus medialis using bidimensional arrays.
  
  
  RESULTS
  Central and peripheral fatigue were described as decreases in FD and CV, respectively. A positive correlation between FD and CV (R=0.51, p<0.01) was found during the sustained 60% MVC, probably as a result of simultaneous motor unit synchronization and a decrease in muscle fiber CV during the fatiguing task.
  
  
  CONCLUSIONS
  Central and peripheral fatigue can be described as changes in FD and CV, at least in young, healthy women. The significant correlation between FD and CV observed at 60% MVC suggests that a mutual interaction between central and peripheral fatigue can arise during submaximal isometric contractions.
authors.affiliation: Rehabilitation Research Laboratory, Department of Business Economics, Health and Social Care, University of Applied Sciences and Arts of Southern Switzerland, SUPSI, Manno, Switzerland.
authors.forename: Matteo
authors.initials: M
authors.lastname: Beretta-Piccoli
authors.affiliation: Department of Molecular Medicine and Sport Medicine Centre Voghera, University of Pavia, Pavia, Italy.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: D'Antona
authors.affiliation: Rehabilitation Research Laboratory, Department of Business Economics, Health and Social Care, University of Applied Sciences and Arts of Southern Switzerland, SUPSI, Manno, Switzerland.
authors.forename: Marco
authors.initials: M
authors.lastname: Barbero
authors.affiliation: Division of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, United States of America.
authors.forename: Beth
authors.initials: B
authors.lastname: Fisher
authors.affiliation: Division of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, United States of America.
authors.forename: Christina M
authors.initials: CM
authors.lastname: Dieli-Conwright
authors.affiliation: Department of Business Economics, Health and Social Care, University of Applied Sciences and Arts of Southern Switzerland, SUPSI, Landquart, Switzerland.
authors.forename: Ron
authors.initials: R
authors.lastname: Clijsen
authors.affiliation: Rehabilitation Research Laboratory, Department of Business Economics, Health and Social Care, University of Applied Sciences and Arts of Southern Switzerland, SUPSI, Manno, Switzerland.
authors.forename: Corrado
authors.initials: C
authors.lastname: Cescon
mesh_terms: D000328:Adult; D004558:Electric Stimulation; D004576:Electromyography; D016552:Ergometry / Q000379:methods; D005260:Female; D017709:Fractals; D006801:Humans; D007537:Isometric Contraction; D018763:Muscle Fatigue / Q000502:physiology*; D052097:Quadriceps Muscle / Q000502:physiology*; D012815:Signal Processing, Computer-Assisted; D055815:Young Adult