Changes in muscle strength, muscle fibre size and myofibrillar gene expression after immobilization and retraining in humans

Abstract

Changes in muscle strength, vastus lateralis fibre characteristics and myosin heavy‐chain (MyoHC) gene expression were examined in 48 men and women following 3 weeks of knee immobilization and after 12 weeks of retraining with 1866 eccentric, concentric or mixed contractions. Immobilization reduced eccentric, concentric and isometric strength by 47 %. After 2 weeks of spontaneous recovery there still was an average strength deficit of 11 %. With eccentric and mixed compared with concentric retraining the rate of strength recovery was faster and the eccentric and isometric strength gains greater. Immobilization reduced type I, IIa and IIx muscle fibre areas by 13, 10 and 10 %, respectively and after 2 weeks of spontaneous recovery from immobilization these fibres were 5 % smaller than at baseline. Hypertrophy of type I, IIa and IIx fibres relative to baseline was 10, 16 and 16 % after eccentric and 11, 9 and 10 % after mixed training (all P < 0.05), exceeding the 4, 5 and 5 % gains after concentric training. Type IIa and IIx fibre enlargements were greatest after eccentric training. Total RNA/wet muscle weight and type I, IIa and IIx MyoHC mRNA levels did not change differently after immobilization and retraining. Immobilization downregulated the expression of type I MyoHC mRNA to 0.72‐fold of baseline and exercise training upregulated it to 0.95 of baseline. No changes occurred in type IIa MyoHC mRNA. Immobilization and exercise training upregulated type IIx MyoHC mRNA 2.9‐fold and 1.2‐fold, respectively. For the immobilization segment, type I, IIa and IIx fibre area and type I, IIa and IIx MyoHC mRNA correlated (r= 0.66, r= 0.07 and r=−0.71, respectively). The present data underscore the role muscle lengthening plays in human neuromuscular function and adaptation.

A mechanism for increased contractile strength of human pennate muscle in response to strength training: changes in muscle architecture

“…Comparable evidence of a preferential or more pronounced type II fibre hypertrophy in response to heavy resistance training has been reported previously (e.g. Hather et al 1991;Roman et al 1993;Volek et al 1999;Kadi et al 1999;Andersen & Aagaard, 2000;Hortobagyi et al 2000). Apparently, type II muscle fibres seem to possess a greater adaptive responsiveness to the intense muscle-loading regimes associated with heavy-resistance training.…”

Muscle size, neuromuscular activation, and rapid force characteristics in elderly men and women: effects of unilateral long-term disuse due to hip-osteoarthritis

“…This is contrasted by the fact that the elderly population more often undergoes periods of immobilization and disuse, not only due to joint pain, but also due to a higher degree of comorbidity and hospitalization (32). Studies in healthy young adults have demonstrated that immobilization leads to rapid decreases in maximal muscle strength, muscle mass, and neural activation (4,19); however, recent studies indicate that skeletal muscle in aged animals and humans is more vulnerable to muscle unloading than that in young individuals (8,41). Furthermore, recent data from Yasuda et al (43) show that there might be a gender-specific response to unloading, as evidenced by a more pronounced decrease in specific strength in young women compared with young men after 14 days of unilateral limb immobilization.…”

Early Application of Negative Work via Eccentric Ergometry Following Anterior Cruciate Ligament Reconstruction: A Case Report

“…Originally utilized as a paradigm for studying muscle damage, recent research suggests that controlled application of negative work is a potent stimulus for increasing muscle size and strength, which are the predominant impairments following ACL-R. Hortobagyi et al 10 compared a 12-week ECC versus concentric (CON) resistance training program via an isokinetic dynamometer after 3 weeks of knee immobilization on healthy college-age men and women. Improvements in muscle size in the ECC group were nearly double those of the CON group.…”