Dynamic contractility and efficiency impairments in stretch-shortening cycle are stretch-load-dependent after traininginduced muscle damage

Mark Vaczi, Levente Racz, Tibor Hortobagyi, Jozsef Tihanyi

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To determine the acute task and stretch-load dependency of neuromuscular impairments after muscle-damaging exercises, we examined the magnitude of strength deficits in isometric and stretch-shortening cycle (SSC) contractions after a single bout of exercise. Ten trained men performed 90 unilateral isokinetic eccentric-concentric knee extensions on a dynamometer. Plasma creatine kinase activity, muscle soreness, maximal isometric torque, short-range stiffness, and peak torque in the eccentric phase of the SSC contraction at 3 stretch-loads (120, 150, and 180 J) were determined in the quadriceps before and 24 hours after exercise. During SSC, positive mechanical work and efficiency were also calculated. Creatine kinase and soreness increased at 24 hours (p < 0.05). In each of the 3 stretchload conditions, muscle damage affected short-range stiffness less than isometric and peak SSC torque (p < 0.05), providing evidence for a selective impairment in contractile function after muscle damage. With greater SSC stretch-load peak, SSC torque deficit increased linearly, whereas short-range stiffness deficit was unaffected. Efficiency declined only at the 180-J condition (p < 0.05) as a result of decreased positive work (p < 0.05). It was concluded that intense exercise produced microtrauma in the muscle, and a selective loss of force generating capacity, which suggests greater damage to the contractile machinery. Practitioners may expect greater acute impairment of force generation in movements that use large loads in their daily training drills. However, altered knee flexion strategy during SSC may compensate for the force deficit, preserving mechanical efficiency at smaller stretchloads.

Original languageEnglish
Pages (from-to)2171-2179
Number of pages9
JournalJournal of Strength and Conditioning Research
Issue number8
Publication statusPublished - Aug 1 2013



  • Isokinetic training
  • Knee extensor
  • Microinjury
  • Stretching energy

ASJC Scopus subject areas

  • Orthopedics and Sports Medicine
  • Physical Therapy, Sports Therapy and Rehabilitation

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