title: Effects of Contract-Relax, Static Stretching, and Isometric Contractions on Muscle-Tendon Mechanics.
abstract: BACKGROUND
  Loading characteristics of stretching techniques likely influence the specific mechanisms responsible for acute increases in range of motion (ROM). Therefore, the effects of a version of contract-relax (CR) proprioceptive neuromuscular facilitation stretching, static stretching (SS), and maximal isometric contraction (Iso) interventions were studied in 17 healthy human volunteers.
  
  
  METHODS
  Passive ankle moment was recorded on an isokinetic dynamometer, with EMG recording from the triceps surae, simultaneous real-time motion analysis, and ultrasound-imaging-recorded gastrocnemius medialis muscle and Achilles tendon elongation. Subjects then performed each intervention randomly on separate days before reassessment.
  
  
  RESULTS
  Significant increases in dorsiflexion ROM (2.5°-5.3°; P < 0.01) and reductions in whole muscle-tendon stiffness (10.1%-21.0%; P < 0.01) occurred under all conditions, with significantly greater changes detected following CR stretching (P < 0.05). Significant reductions in tendon stiffness were observed after CR stretching and Iso (17.7%-22.1%; P < 0.01) but not after SS (P > 0.05), whereas significant reductions in muscle stiffness occurred after CR stretching and SS (16.0%-20.5%; P < 0.01) but not after Iso (P > 0.05). Increases in peak passive moment (stretch tolerance) occurred after Iso (6.8%; P < 0.05), CR stretching (10.6%; P = 0.08), and SS (5.2%; P = 0.08); no difference in changes between conditions was found (P > 0.05). Significant correlations (rs = 0.69-0.82; P < 0.01) were observed between changes in peak passive moment and maximal ROM under all conditions.
  
  
  CONCLUSIONS
  Although similar ROM increases occur after Iso and SS, changes in muscle and tendon stiffness are distinct. Concomitant reductions in muscle and tendon stiffness after CR stretching suggest a broader adaptive response that likely explains its superior efficacy in acutely increasing ROM. Although mechanical changes appear tissue-specific between interventions, similar increases in stretch tolerance after all interventions are strongly correlated with changes in ROM.
authors: 1Sport, Exercise, and Life Sciences, The University of Northampton, Northampton, UNITED KINGDOM; and 2Center for Exercise and Sport Science Research, School of Exercise and Health Sciences, Edith Cowan University, Joondalup, AUSTRALIA.
authors: Anthony D
authors: AD
authors: Kay
authors: Jade
authors: J
authors: Husbands-Beasley
authors: Anthony J
authors: AJ
authors: Blazevich
mesh_terms: D000125:Achilles Tendon / Q000502:physiology*; D000293:Adolescent; D000328:Adult; D000843:Ankle Joint / Q000502:physiology; D001696:Biomechanical Phenomena; D004576:Electromyography; D005260:Female; D006801:Humans; D007537:Isometric Contraction; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D009126:Muscle Relaxation / Q000502:physiology; D052580:Muscle Stretching Exercises / Q000379:methods*; D018482:Muscle, Skeletal / Q000502:physiology*; D016059:Range of Motion, Articular; D055815:Young Adult