title: Effect of exercise-induced muscle damage on muscle hardness evaluated by ultrasound real-time tissue elastography.
abstract: OBJECTIVE
  To assess the effect of exercise-induced muscle damage on muscle hardness and evaluate the relationship between muscle hardness and muscle damage indicators.
  
  
  METHODS
  Seven men (mean 25.3 years; 172.7 cm; 66.8 kg) performed the single-leg ankle plantar flexion exercise involving both concentric and eccentric contractions (10 sets of 40 repetitions). The hardness of the medial gastrocnemius (MG) was evaluated using ultrasound real-time tissue elastography before, from day 1 to 4, and day 7 after exercise. The strain ratio between the MG and a reference material was calculated. Simultaneously, we evaluated the magnetic resonance T2 value (an index of edema) of the triceps surae, the ankle dorsiflexion range of motion (ROM), and calf muscle soreness. Serum creatine kinase activity was assessed before, 2 and 4 h, and from day 1 to 4 after exercise.
  
  
  RESULTS
  The MG showed lower strain ratio, indicating increased muscle hardness, on day 4 post-exercise (P < 0.01) and higher T2 values on days 1-7 post-exercise (P < 0.01) relative to each pre-exercise value. The ankle dorsiflexion ROM was lower on days 2-4 post-exercise (P < 0.01). The serum creatine kinase markedly increased on days 3 and 4 post-exercise (not significant). The degree of muscle soreness among the post-exercise time points was similar. The decreased strain ratio did not correlate with the increased T2, the decreased joint ROM or muscle soreness.
  
  
  CONCLUSIONS
  Muscle hardness increased after strenuous resistance exercise, but the change was not related with muscle edema, decreased joint ROM, or muscle soreness resulting from muscle damage.
authors.affiliation: Faculty of Business and Information Sciences, Jobu University, 634-1 Toyazuka-machi, Isesaki, Gunma 372-8588 Japan.
authors.forename: Osamu
authors.initials: O
authors.lastname: Yanagisawa
authors.affiliation: Department of Health Science, Musashigaoka Junior College, 111-1 Minamiyoshimi, Yoshimi-cho, Hiki, Saitama 355-0154 Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Sakuma
authors.affiliation: Faculty of Sport Sciences, Waseda University, 2-579-15 Mikajima, Tokorozawa, Saitama 359-1192 Japan.
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Kawakami
authors.affiliation: Faculty of Sport Sciences, Waseda University, 2-579-15 Mikajima, Tokorozawa, Saitama 359-1192 Japan.
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Suzuki
authors.affiliation: Faculty of Sport Sciences, Waseda University, 2-579-15 Mikajima, Tokorozawa, Saitama 359-1192 Japan.
authors.forename: Toru
authors.initials: T
authors.lastname: Fukubayashi
keywords: Eccentric contraction; Magnetic resonance imaging; Muscle damage; Muscle edema; Muscle hardness; Real-time tissue elastography