title: Effect of surface stiffness on the neural control of stretch-shortening cycle movements.
abstract: OBJECTIVE
  It is accepted that leg stiffness (Kleg ) increases when surface stiffness decreases, and vice versa. However, little is known how the central nervous system fulfils this task. To understand the effect of surface stiffness on the neural control of stretch-shortening cycle movements, this study aimed to compare modulation of spinal and corticospinal excitability at distinct phases after ground contact during two-legged hopping when changing from solid to elastic ground.
  
  
  METHODS
  Motor-evoked potentials (MEPs) induced by transcranial magnetic stimulation (TMS) and H-reflexes were elicited at the time of the short (SLR)-, medium (MLR)- and long (LLR)-latency responses of the soleus muscle (SOL) during two-legged hopping on different stiffness surfaces, elastic and stiff.
  
  
  RESULTS
  Soleus H-reflexes during two-legged hopping on the elastic surface were lower at SLR and larger at LLR than on the stiff surface (P < 0.05 for both comparisons). SOL MEP size was higher at the time of SLR during hopping on the elastic surface than on the stiff surface (P < 0.05) although the background EMG was similar.
  
  
  CONCLUSIONS
  It is argued that this phase-specific adaptation in spinal reflex excitability is functionally relevant to adjust leg stiffness to optimally exploit the properties of the elastic surface. Thus, the increased corticospinal excitability on the elastic surface may reflect a more supraspinal control of the ankle muscles to compensate the decrease in reflexive stiffness at the beginning of touchdown and/or counteract the higher postural challenges associated with the elastic surface.
authors: Departamento de Ciencias de la Actividad Física y del Deporte, Facultad de Ciencias de la Actividad Física y del Deporte, UCAM, Universidad Católica San Antonio, Murcia, Spain.
authors: G
authors: G
authors: Márquez
authors: L
authors: L
authors: Morenilla
authors: W
authors: W
authors: Taube
authors: M
authors: M
authors: Fernández-del-Olmo
mesh_terms: D000328:Adult; D004576:Electromyography / Q000379:methods; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006181:H-Reflex / Q000502:physiology*; D006801:Humans; D008297:Male; D009068:Movement / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation* / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation / Q000379:methods
keywords: H-reflex; leg stiffness; stretch-shortening cycle; transcranial magnetic stimulation