title: Muscle and tendon stiffness assessment using the alpha method and ultrafast ultrasound.
abstract: OBJECTIVE
  The alpha method enables the dissociation of the passive (i.e., tendinous tissues) and active (i.e., fascicles) part of muscle-tendon stiffness. It is based on two main assumptions (i.e., a constant tendon stiffness and a muscle stiffness proportional to the torque produced), which have not been approved in vivo. The purpose of this study was to validate these two assumptions using ultrafast ultrasound, and to compare fascicle and tendon stiffness as determined by both methods.
  
  
  METHODS
  Ten healthy males performed a fast-stretch experiment on the ankle plantar flexors. The mathematical model of the alpha method allowed to estimate the stiffness of muscle and tendinous tissues on the basis of the assumptions associated to the behaviors of muscle fascicles and tendinous tissues. Muscle and tendon stiffness of the gastrocnemius medialis were also calculated from ultrafast ultrasound measurements.
  
  
  RESULTS
  Muscle stiffness measured by the ultrasound method increased from 217 ± 83 to 720 ± 265 N/mm with an increasing level of force (from 30 to 90 % MVC). Tendinous stiffness measured by the ultrasound method remained constant across the force level (P < 0.001). However, the stiffness values obtained with both methods were significantly different (P < 0.001).
  
  
  CONCLUSIONS
  In conclusion, these findings validate the two main assumptions underlying the alpha method using ultrasound. Differences in stiffness values obtained with alpha and ultrasound methods could be associated with physiological and geometrical differences between the whole plantar flexors muscles characterized by the alpha method and the gastrocnemius medialis assessed with the ultrasound method.
authors: Laboratory "Movement, Interactions, Performance" (EA 4334), University of Nantes, UFR STAPS, 25 bis boulevard Guy Mollet, BP 72206, 44322, Nantes Cedex 3, France.
authors: Hugo
authors: H
authors: Hauraix
authors: Alexandre
authors: A
authors: Fouré
authors: Sylvain
authors: S
authors: Dorel
authors: Christophe
authors: C
authors: Cornu
authors: Antoine
authors: A
authors: Nordez
mesh_terms: D000328:Adult; D000842:Ankle / Q000502:physiology; D000843:Ankle Joint / Q000502:physiology*; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology*; D013710:Tendons / Q000502:physiology*; D019415:Torque; D055815:Young Adult