Extracellular matrix remodeling and its contribution to protective adaptation following lengthening contractions in XXXX muscle.

@entity1 @entity1414 @entity13239 @entity2533 @entity5938
This study determined the contribution of extracellular matrix (ECM) remodeling to the protective adaptation of @entity1 skeletal muscle known as the repeated-bout effect (RBE). Muscle biopsies were obtained 3 hours, 2 days, and 27 days following an initial bout (B1) of lengthening contractions (LCs) and 2 days following a repeated bout (B2) in 2 separate studies. Biopsies from the nonexercised legs served as controls. In the first study, global transcriptomic analysis indicated widespread changes in ECM structural, deadhesive, and signaling transcripts, 3 hours following LC. To determine if ECM remodeling is involved in the RBE, we conducted a second study by use of a repeated-bout paradigm. TNC immunoreactivity increased 10.8-fold following B1, was attenuated following B2, and positively correlated with LC-induced strength loss (r(2) = 0.45; P = 0.009). Expression of collagen I, III, and IV ( @entity13239 , @entity1414 , @entity5938 ) transcripts was unchanged early but increased 5.7    2.5-, 3.2    0.9-, and 2.1    0.4-fold (P < 0.05), respectively, 27 days post-B1 and were unaffected by B2. Likewise, @entity2533 signaling demonstrated a delayed response following LC. Satellite cell content increased 80% (P < 0.05) 2 days post-B1 (P < 0.05), remained elevated 27 days post-B1, and was unaffected by B2. Collectively, the data suggest sequential ECM remodeling characterized by early deadhesion and delayed reconstructive activity that appear to contribute to the RBE.
