Open AccessArchitectural and mechanical properties of the rat adductor longus: Response to weight‐lifting training
Author(s) -
Roy Roland R.,
Wilson Roberta,
Edgerton V. Reggie
Publication year - 1997
Publication title -
the anatomical record
Language(s) - English
Resource type - Journals
eISSN - 1097-0185
pISSN - 0003-276X
DOI - 10.1002/(sici)1097-0185(199702)247:2<170::aid-ar3>3.0.co;2-1
Subject(s) - anatomy , body weight , fiber type , fiber , hindlimb , strength training , weight bearing , medicine , physical medicine and rehabilitation , materials science , surgery , skeletal muscle , composite material
Background The primary objective of this study was to determine the effects of an 8 week weight‐lifting program on the mechanical, histochemical, and architectural properties of the rat adductor longus muscle, a predominantly slow adductor muscle. Methods The weight‐lifting program was progressive such that the rats were performing three bouts of ten lifts with 300% body weight load every other day during the last 3 weeks of training. The in situ mechanical properties, fiber type composition, and architectural characteristics of the muscle were determined in control and weight‐trained rats. Intramuscular electromyographic recordings were used to verify the recruitment of the adductor longus during the lifting task. Results The adductor longus was composed predominantly of slow fibers (˜80% slow oxidative) and had a relatively simple architectural design, i.e., one motor end‐plate band near the center of the muscle, virtually no angle of pinnation of the fibers from the line of pull, and a fiber length:muscle length ratio of 0.72. The mean fiber type composition and fiber size, the total fiber number, and the mean physiological cross‐sectional area of the adductor longus were similar in the two groups of rats. The mean body weight of weight‐lifting rats was significantly less than control. The weight of the adductor longus relative to body weight and its fatigue resistance were higher and the maximum rate of shortening was slower in weight‐lifting than in control rats. No other mechanical property was significantly affected by the training program. Conclusions The results indicate that approximately 1 minute of overload every other day by physiological recruitment of motor units can induce remodeling of the adductor longus of growing rats; i.e., the trained muscles were slower and less fatigable than control. Given that the effects on the architectural or force‐generating properties of the muscles were small, the marked improvement in the ability to lift heavier loads as the training progressed appears to be more attributable to neurally related than to muscle‐related phenomena. Anat. Rec. 247:170‐178, 1997. © 1997 Wiley‐Liss, Inc.