title: Muscle hardness measurement by using ultrasound elastography: a feasibility study.
abstract: BACKGROUND
  Muscle hardening, including delayed onset muscle soreness, can be found after vigorous exercise. Some techniques for measuring muscle hardness have been proposed. Freehand ultrasound (US) elastography has been developed and applied to breast imaging.
  
  
  OBJECTIVE
  To evaluate the feasibility of US elastography for investigating changes in muscle hardness after eccentric exercise of the elbow flexor muscles.
  
  
  METHODS
  Six healthy male volunteers performed eccentric contractions of the elbow flexor muscles of their non-dominant arms. US elastography was performed by using 14-6 MHz linear array transducer combined with a stabilizer and a gel pack of reference agent. Color-coded elasticity images and the relative strain ratio of the biceps brachii muscle to the reference were obtained. To verify the US elastography measurements, a commercially available durometer was also employed. Both measurements were performed before, immediately after, and 1-4 days after exercise. The mean scores of strain ratios of the US elastography and durometer measurements were examined using repeated-measures ANOVA.
  
  
  RESULTS
  US elastography demonstrated significant muscle hardening and recovery after exercise (P<0.01). Muscle hardness increased up immediately after the exercise and continued to increase, peaking on day 2 post-exercise, and then decreased until day 4. The durometer indicated similar changes to US elastography. The control arms did not demonstrate any significant change.
  
  
  CONCLUSIONS
  US elastography is feasible to measure muscle hardness and to produce a two-dimensional hardness map of the muscle.
authors.affiliation: Department of Radiology, Faculty of Health Sciences, Tokyo Metropolitan University, Tokyo, Japan. niitsu2121@gmail.com
authors.forename: Mamoru
authors.initials: M
authors.lastname: Niitsu
authors.forename: Akie
authors.initials: A
authors.lastname: Michizaki
authors.forename: Asako
authors.initials: A
authors.lastname: Endo
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Takei
authors.forename: Osamu
authors.initials: O
authors.lastname: Yanagisawa
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D054459:Elasticity Imaging Techniques / Q000379:methods*; D004550:Elbow / Q000000981:diagnostic imaging; D015444:Exercise / Q000502:physiology; D005240:Feasibility Studies; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging*; D012016:Reference Values; D055070:Resistance Training / Q000379:methods; D014891:Weight Lifting / Q000502:physiology; D055815:Young Adult