Adaptation of rat soleus muscles to 4 wk of intermittent strain.
Stauber-WT; Miller-GR; Grimmett-JG; Knack-KK
J Appl Physiol 1994 Jul; 77(1):58-62
The hypothesis that different stretching protocols produce different responses from the soleus muscle when subjected to chronic intermittent stretching was investigated in the female Sprague- Dawley-rat. Anesthetized rats were subjected to repeated soleus muscle strain overloads every other day for 4 weeks. The soleus muscle was electrically stimulated, and the dorsum of the foot was moved through its range of motion ten times in 13 seconds (slow stretch) or 5 seconds (fast stretch). On physical examination, following a month of repeated dynamic stretching, the soleus muscles seemed to be larger and there was no apparent evidence of fibrosis or scarring. Muscles which had been slow stretched had a mass 12.8% greater than the mass of the contralateral muscle. This increased mass resulted from myofiber hypertrophy. The fast stretched muscles increased in mass by 10.4%. The fast stretched soleus muscles contained a variety of different fiber sizes, ranging from normal to small with cross sectional areas of less than 60 square micrometers. Widened interstitial spaces in the fast stretched muscles accounted for their increased mass. In the slow stretched muscles, a typical hypertrophy response was documented without the presence of small fibers. The authors indicate that there appeared to be two distinct populations of fibers for the fast stretched muscles: a small fiber population and a normal sized fiber population. This was verified by image analysis. The authors conclude that the stretch overloaded rat soleus muscle offers a model for studying muscle adaptation in response to material fatigue. The nature of these responses and the stimulus for their development is not clear.
NIOSH-Publication; NIOSH-Grant; Musculoskeletal-system-disorders; Physiological-response; Muscle-function; Muscle-stress; Muscle-physiology; Laboratory-animals;
Author Keywords: skeletal muscle; stretch overload; fiber cross-sectional area; muscle hypertrophy; noncontractile tissue
Physiology West Virginia University 3051 Health Sciences North Morgantown, WV 26506
Journal of Applied Physiology
West Virginia University, Morgantown, West Virginia