Neural and mechanical responses of the triceps surae muscle group after 1 h of repeated fast passive stretches

• Published in: Journal of applied physiology (1985) Vol. 96; no. 6; pp. 2325 - 2332
• Main Authors: Avela, Janne, Finni, Taija, Liikavainio, Tuomas, Niemela, Elina, Komi, Paavo V
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Am Physiological Soc 01.06.2004; American Physiological Society
• Subjects: Adult; Ankle Joint - physiology; Biological and medical sciences; Electromyography; Exercise; Fundamental and applied biological sciences. Psychology; Human mechanics; Humans; Male; Motor Activity - physiology; Motor Neurons - physiology; Muscle Contraction - physiology; Muscle, Skeletal - innervation; Muscle, Skeletal - physiology; Muscular system; Nervous system; Reference Values; Reflex, Stretch - physiology; Reflexes; Striated muscle. Tendons; Tendons - physiology; Torque; Vertebrates: osteoarticular system, musculoskeletal system; Osteoarticular system; Biomechanics; Human; Reflex; muscle adaptation; muscle stretch; Triceps surae muscle; Striated muscle; Stretching; Tendon
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.01010.2003

Neuromuscular Research Center, Department of Biology of Physical Activity, University of Jyväskylä, FIN-40100 Jyväskylä, Finland Submitted 16 September 2003 ; accepted in final form 5 February 2004 Experiments were carried out to examine interaction between mechanical changes of the muscletendon unit and reduced reflex sensitivity after repeated and prolonged passive muscle stretching (RPS). There is some evidence that this interaction might be relevant also during active stretch-shortening cycle type of fatigue tasks. The results demonstrated a clear deterioration of voluntarily and electrically induced muscle contractions after RPS. Maximal voluntary contraction (MVC), average electromyographic activities of the gastrocnemius and soleus muscles, and maximal twitch contraction decreased on average by 13.8, 10.4, 7.6, and 16.8%, respectively. In addition, there was a 14% lengthening in the total duration of the twitch. MVCs measured at different ankle joint angles revealed a downward and rightward shift in the torquefascicle length curve after RPS. Interestingly, there was a crossing in the torque-fascicle length curves while measured at different activation levels but at the same joint angle before and after RPS. Even though no changes were observed in the activation level during MVCs, all the reflex parameters showed a clear reduction after RPS. This study presents evidence that repeated and prolonged passive muscle stretching can lead to some modification of material behavior of the aponeurosis-tendon system, such as stress relaxation and/or plastic deformation. In addition, altered material properties seem to affect proprioceptive feedback and, therefore, the motor unit activation in proportion to the contractile failure. muscle stretch; reflex; muscle adaptation Address for reprint requests and other correspondence: J. Avela, Neuromuscular Research Center, Dept. of Biology of Physical Activity, Univ. of Jyväskylä, FIN-40100 Jyväskylä, Finland (E-mail: avela{at}sport.jyu.fi ).