Muscular enlargement and number of fibers in skeletal muscles of rats

Abstract

The effect of muscular enlargement produced by surgical ablation of a synergist and the combination of synergist ablation and exercise on the number of fibers in the soleus (S), plantaris (P), and extensor digitorum longus (EDL) muscles of the rat was studied. The number of fibers per muscle was determined by direct counts of individual fibers dissected from HNO3-treated muscles. Ablation of a synergist produced average enlargements of about 25, 45, and 29% for the S, P, and EDL muscles, respectively. Exercise and synergist ablation produced increases in wet weight to about 44 and 88% for the S and P muscles, respectively, whereas no further increases were observed in the EDL muscles. Intra-animal comparisons revealed that no differences existed for total fiber number or the incidence of fibers with bifurcations between the enlarged and contralateral control muscles. The difference in dry weight of fibers from the enlarged as compared with control muscles was closely correlated to differences in total muscle wet weight. These data demonstrate that hypertrophy rather than hyperplasia was responsible for increases from 10 to over 100% in the weight of skeletal muscles.

Specific force of the rat plantaris muscle changes with age, but not with overload

“…As we suggested previously [1], the relative amount o f non-contractile tissue was not significantly affected by overload. This corresponds to the similar muscle density in control and overloaded muscles [3] and the unchanged content o f myofibrillar protein content throughout the overload period [10], suggesting a similar composition of both muscles. This indicates that the specific force o f the contractile tissue remains unaffected by hypertrophy at all ages.…”

Satellite cell depletion prevents fiber hypertrophy in skeletal muscle

“…Muscle mass can vary considerably, and is modified by hormones, disuse, strength exercise or experimental overload (Egner et al, 2013;Eriksson et al, 2005;Gundersen, 2011;Herbst and Bhasin, 2004). Muscle mass is mainly altered by changing the size of pre-existing muscle fibers, and fiber loss or de novo formation of fibers is believed to play a much lesser role Gollnick et al, 1981;MacDougall et al, 1984;Taylor and Wilkinson, 1986;White et al, 2010).…”

Steep Increase in Myonuclear Domain Size During Infancy

“…Benard et al showed with a threedimensional ultrasound analysis that fiber length increases proportionally to tibia length in human medial gastrocnemius medial muscle between 5 and 12 years of age (Benard et al, 2011). Furthermore, the consensus is that the number of muscle fibers is set at birth (Gollnick et al, 1981), but some investigators have reported that postnatal muscle growth may be realized to some extent by an increase in number of fibers (Sjostrom et al, 1991;Antonio and Gonyea, 1993;Tamaki and Uchiyama, 1995). These changes however do not affect the parameters used in our study, as they are normalized to the muscle volume contained within a 5-lm cross-section.…”