Key Points
- To examine how immobilization in stretched versus shortened positions alters muscle mass, RNA levels, and protein turnover in non-weight-bearing rat hind limbs.
- Non-weight-bearing rat hind limbs were immobilized in dorsiflexion (stretch) or shortening, with comparisons made to contralateral freely moving and weight-bearing control limbs.
- Assessed changes in muscle mass, total RNA content, myofibrillar and sarcoplasmic protein levels, and in vivo and in vitro rates of protein synthesis and proteolysis.
- Dorsiflexion-induced stretching of the unloaded soleus muscle caused hypertrophy relative to weight-bearing controls, stimulated sarcoplasmic protein synthesis, increased RNA, and reduced proteolysis.
- Unloading of freely moving soleus muscles depleted myofibrillar proteins and led to slower protein synthesis alongside accelerated protein degradation compared to weight-bearing controls.
- Shortening immobilization of the extensor digitorum longus reduced overall muscle growth, slowed in vitro protein synthesis, and decreased RNA levels relative to the contralateral freely moving muscle.
Structured PICO
PPopulationRats (hind limb muscles)
IInterventionImmobilization (dorsiflexion/stretching or shortening) under non-weight-bearing conditions
CComparatorWeight-bearing controls and contralateral freely moving muscles
OOutcomeMuscle mass and protein metabolism (synthesis and degradation)surrogate
Stretching of unloaded muscles prevents the loss of mass and protein metabolism changes typically seen with unloading.