title: Plyometric training improves voluntary activation and strength during isometric, concentric and eccentric contractions.
abstract: OBJECTIVE
  This study investigated effects of plyometric training (6 weeks, 3 sessions/week) on maximum voluntary contraction (MVC) strength and neural activation of the knee extensors during isometric, concentric and eccentric contractions.
  
  
  METHODS
  Twenty-seven participants were randomly assigned to the intervention or control group.
  
  
  METHODS
  Maximum voluntary torques (MVT) during the different types of contraction were measured at 110° knee flexion (180°=full extension). The interpolated twitch technique was applied at the same knee joint angle during isometric, concentric and eccentric contractions to measure voluntary activation. In addition, normalized root mean square of the EMG signal at MVT was calculated. The twitch torque signal induced by electrical nerve stimulation at rest was used to evaluate training-related changes at the muscle level. In addition, jump height in countermovement jump was measured.
  
  
  RESULTS
  After training, MVT increased by 20Nm (95% CI: 5-36Nm, P=0.012), 24Nm (95% CI: 9-40Nm, P=0.004) and 27Nm (95% CI: 7-48Nm, P=0.013) for isometric, concentric and eccentric MVCs compared to controls, respectively. The strength enhancements were associated with increases in voluntary activation during isometric, concentric and eccentric MVCs by 7.8% (95% CI: 1.8-13.9%, P=0.013), 7.0% (95% CI: 0.4-13.5%, P=0.039) and 8.6% (95% CI: 3.0-14.2%, P=0.005), respectively. Changes in the twitch torque signal of the resting muscle, induced by supramaximal electrical stimulation of the femoral nerve, were not observed, indicating no alterations at the muscle level, whereas jump height was increased.
  
  
  CONCLUSIONS
  Given the fact that the training exercises consisted of eccentric muscle actions followed by concentric contractions, it is in particular relevant that the plyometric training increased MVC strength and neural activation of the quadriceps muscle regardless of the contraction mode.
authors.affiliation: Department of Exercise Science, University of Rostock, Germany. Electronic address: martin.behrens@uni-rostock.de.
authors.forename: Martin
authors.initials: M
authors.lastname: Behrens
authors.affiliation: Department of Orthopaedics, University Medicine Rostock, Germany.
authors.forename: Anett
authors.initials: A
authors.lastname: Mau-Moeller
authors.affiliation: Department of Pediatrics, University Medicine Rostock, Germany.
authors.forename: Karoline
authors.initials: K
authors.lastname: Mueller
authors.affiliation: Department of Exercise Science, University of Rostock, Germany.
authors.forename: Sandra
authors.initials: S
authors.lastname: Heise
authors.affiliation: Department of Exercise Science, University of Rostock, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Gube
authors.affiliation: Department of Exercise Science, University of Rostock, Germany.
authors.forename: Nico
authors.initials: N
authors.lastname: Beuster
authors.affiliation: Department of Traumatology, Hand and Reconstructive Surgery, University Medicine Rostock, Germany.
authors.forename: Philipp K E
authors.initials: PK
authors.lastname: Herlyn
authors.affiliation: Department of Pediatrics, University Medicine Rostock, Germany.
authors.forename: Dagmar-C
authors.initials: DC
authors.lastname: Fischer
authors.affiliation: Department of Exercise Science, University of Rostock, Germany.
authors.forename: Sven
authors.initials: S
authors.lastname: Bruhn
mesh_terms: D000328:Adult; D004576:Electromyography; D005260:Female; D006801:Humans; D007717:Knee / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D053580:Muscle Strength / Q000502:physiology*; D059385:Plyometric Exercise; D052097:Quadriceps Muscle / Q000502:physiology; D019415:Torque
keywords: Interpolated twitch technique; M-wave; Quadriceps; Stretch-shortening cycle; Twitch torque