title: Role of the trunk during drop jumps on stable and unstable surfaces.
abstract: BACKGROUND
  The present study investigated associations between trunk muscle strength, jump performance, and lower limb kinematics during drop jumps on stable and unstable surfaces. Next to this behavioral approach, correlations were also computed on a neuromuscular level between trunk and leg muscle activity during the same test conditions.
  
  
  METHODS
  Twenty-nine healthy and physically active subjects (age 23 ± 3 years) were enrolled in this study. Peak isokinetic torque (PIT) of the trunk flexors and extensors was assessed separately on an isokinetic device. In addition, tests included drop jumps (DJ) on a force plate under stable and unstable (i.e., balance pad on top of the force plate) surfaces. Lower limb kinematics as well as electromyographic activity of selected trunk and leg muscles were analyzed.
  
  
  RESULTS
  Significant positive but small correlations (0.50 ≤ r ≤ 0.66, p < 0.05) were detected between trunk extensor PIT and athletic performance measures (i.e., DJ height, DJ performance index), irrespective of surface condition. Further, significant negative but small correlation coefficients were examined between trunk extensor PIT and knee valgus motion under stable and unstable surface conditions (-0.48 ≤ r ≤ -0.45, p < 0.05). In addition, significant positive but small correlations (0.45 ≤ r ≤ 0.68, p < 0.05) were found between trunk and leg muscle activity, irrespective of surface condition.
  
  
  CONCLUSIONS
  Behavioral and neuromuscular data from this study indicate that, irrespective of the surface condition (i.e., jumping on stable or unstable ground), the trunk plays a minor role for leg muscle performance/activity during DJ. This implies only limited effects of trunk muscle strengthening on jump performance in the stretch-shortening cycle.
authors.affiliation: Division of Training and Movement Science, Cluster of Excellency in Cognition Sciences, University of Potsdam, Am Neuen Palais 10, Haus 12, 14469, Potsdam, Germany, prieske@uni-potsdam.de.
authors.forename: Olaf
authors.initials: O
authors.lastname: Prieske
authors.forename: Thomas
authors.initials: T
authors.lastname: Muehlbauer
authors.forename: Tom
authors.initials: T
authors.lastname: Krueger
authors.forename: Armin
authors.initials: A
authors.lastname: Kibele
authors.forename: David G
authors.initials: DG
authors.lastname: Behm
authors.forename: Urs
authors.initials: U
authors.lastname: Granacher
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D035002:Lower Extremity / Q000502:physiology; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology; D004856:Postural Balance; D060726:Torso / Q000502:physiology*