title: Modulation of Stretch-Shortening-Cycle Behavior With Eccentric Loading of Triceps Surae: A Possible Therapeutic Mechanism.
abstract: BACKGROUND
  Eccentric exercises are increasingly being used to treat lower-limb musculoskeletal conditions such as Achilles tendinopathy. Despite widespread clinical application and documented efficacy, mechanisms underpinning clinical benefit remain unclear. Positive adaptations in motor performance are a potential mechanism.
  
  
  OBJECTIVE
  To investigate how an eccentric loading intervention influences measures of stretch-shortening-cycle (SSC) behavior during a hopping task.
  
  
  METHODS
  Within-subjects repeated-measures observational study.
  
  
  METHODS
  University motion-analysis laboratory.
  
  
  METHODS
  Healthy adults.
  
  
  METHODS
  A single intervention of 5 sets of 10 eccentric plantar-flexion contractions at 6 repetitions maximum using a commercial seated calf-raise machine.
  
  
  METHODS
  Lower-limb stiffness, sagittal-plane ankle kinematics, and temporal muscle activity of the agonist (soleus) and antagonist (tibialis anterior) muscles, measured during submaximal hopping on a custom-built sledge-jump system.
  
  
  RESULTS
  Eccentric loading altered ankle kinematics during submaximal hopping; peak angle shifted to a less dorsiflexed position by 2.9° and ankle angle precontact shifted by 4.4° (P < .001). Lower-limb stiffness increased from 5.9 to 6.8 N/m (P < .001), while surface EMG measures of soleus occurred 14-44% earlier (P < .001) after the loading intervention.
  
  
  CONCLUSIONS
  These findings suggest that eccentric loading alters SSC behavior in a manner reflective of improved motor performance. Decreased ankle excursion, increased lower-limb stiffness, and alterations in motor control may represent a positive adaptive response to eccentric loading. These findings support the theory that mechanisms underpinning eccentric loading for tendinopathy may in part be due to improved "buffering" of the tendon by the neuromuscular system.
authors.forename: James R
authors.initials: JR
authors.lastname: Debenham
authors.forename: William I
authors.initials: WI
authors.lastname: Gibson
authors.forename: Mervyn J
authors.initials: MJ
authors.lastname: Travers
authors.forename: Amity C
authors.initials: AC
authors.lastname: Campbell
authors.forename: Garry T
authors.initials: GT
authors.lastname: Allison
mesh_terms: D000328:Adult; D000843:Ankle Joint / Q000502:physiology*; D001696:Biomechanical Phenomena / Q000502:physiology; D004576:Electromyography / Q000379:methods; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D035002:Lower Extremity / Q000502:physiology*; D008297:Male; D052580:Muscle Stretching Exercises / Q000379:methods*; D018482:Muscle, Skeletal / Q000502:physiology
keywords: Achilles tendon; eccentric exercise; lower-limb stiffness; motor control