Acute effect of muscle stretching on the steadiness of sustained submaximal contractions of the plantar flexor muscles

• Published in: Journal of applied physiology (1985) Vol. 110; no. 2; pp. 407 - 415
• Main Authors: KATO, Emika, VIEILLEVOYE, Stéphanie, BALESTRA, Costantino, GUISSARD, Nathalie, DUCHATEAU, Jacques
• Format: Journal Article
• Language: English
• Published: Bethesda, MD American Physiological Society 01-02-2011
• Subjects: Adaptation, Physiological - physiology; Adult; Ankle Joint - physiology; Biological and medical sciences; Female; Fundamental and applied biological sciences. Psychology; Humans; Isometric Contraction - physiology; Joints; Male; Muscle Strength - physiology; Muscle Stretching Exercises - methods; Muscle, Skeletal - physiology; Muscular system; Physical Exertion - physiology; Physiology; Stress, Mechanical; Studies; Ultrasonic imaging; force fluctuation; Nervous system diseases; Force; ultrasonography; Acute; Electrophysiology; Striated muscle; muscle architecture; Muscle contraction; Motor control; Equilibrium disorder; Vertebrata; Mammalia; Plantar; Flexor muscle; ENT disease; Electromyography; Stretching
• ISSN: 8750-7587; 1522-1601; 1522-1601
• DOI: 10.1152/japplphysiol.01087.2010

This paper examines the acute effect of a bout of static stretches on torque fluctuation during an isometric torque-matching task that required subjects to sustain isometric contractions as steady as possible with the plantar flexor muscles at four intensities (5, 10, 15, and 20% of maximum) for 20 s. The stretching bout comprised five 60-s passive stretches, separated by 10-s rest. During the torque-matching tasks and muscle stretching, the torque (active and passive) and surface electromyogram (EMG) of the medial gastrocnemius (MG), soleus (Sol), and tibialis anterior (TA) were continuously recorded. Concurrently, changes in muscle architecture (fascicle length and pennation angle) of the MG were monitored by ultrasonography. The results showed that during stretching, passive torque decreased and fascicle length increased gradually. Changes in these two parameters were significantly associated (r(2) = 0.46; P < 0.001). When data from the torque-matching tasks were collapsed across the four torque levels, stretches induced greater torque fluctuation (P < 0.001) and enhanced EMG activity (P < 0.05) in MG and TA muscles with no change in coactivation. Furthermore, stretching maneuvers produced a greater decrease (∼15%; P < 0.001) in fascicle length during the torque-matching tasks and change in torque fluctuation (CV) was positively associated with changes in fascicle length (r(2) = 0.56; P < 0.001), MG and TA EMG activities, and coactivation (r(2) = 0.35, 0.34, and 0.35, respectively; P < 0.001). In conclusion, these observations indicate that repeated stretches can decrease torque steadiness by increasing muscle compliance and EMG activity of muscles around the joint. The relative influence of such adaptations, however, may depend on the torque level during the torque-matching task.