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


  • Authors' present addresses
    D. Fraser: Coastal Arthritis and Rheumatism, PA, 1406 Neuse Boulevard, New Bern, NC 28563, USA.

    J. Lambert: Therapeutic Innovations, Inc., 2706A East 10th Street, Greenville, NC 27858, USA.

Corresponding author
T. Hortobágyi: 251 Ward Sports Medicine Building, East Carolina University, Greenville, NC 27858, USA.


  • 1Changes 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.
  • 2Immobilization 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.
  • 3Immobilization 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.
  • 4Total 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).
  • 5The present data underscore the role muscle lengthening plays in human neuromuscular function and adaptation.