Muscle glycogen concentrations in underfed (HYPO) and refed rats (RE) in an earlier study did not correlate with fatigue. We hypothesized that underfeeding slowed glycolysis in the slow-twitch soleus, but not in the fast-twitch extensor digitorum longus (EDL). Thirty adult male Wistar rats were randomly assigned to receive one of two isovolemic and micronutrient-complete liquid diets, a control...

Fiber type specificity for expression of all three rat skeletal muscle pyruvate dehydrogenase kinase (PDK) isoforms (PDK1, 2, and 4) was determined in fed and 24-h fasted rats. PDK activity and isoform protein and mRNA contents were determined in white gastrocnemius (WG; fast-twitch glycolytic), red gastrocnemius (RG; fast-twitch oxidative), and soleus (Sol; slow-twitch oxidative) muscles. PDK ...

The ubiquitin-proteasome pathway is primarily responsible for myofibrillar protein degradation during hindlimb unweighting (HU). Beta-adrenergic agonists such as clenbuterol (CB) induce muscle hypertrophy and attenuate muscle atrophy due to disuse or inactivity. However, the molecular mechanism by which CB exerts these effects remains poorly understood. The aims of this study were to investigat...

The force produced by cat muscles over time with two stimuli separated by a short interval is approximately three times that produced by a twitch of cat muscles. This facilitation of force production by a second stimulus involves both increases in magnitude and duration of the contraction. Increased magnitude is relatively more important in the fast-twitch plantaris muscle, whereas increased du...

At the start of a rowing race, the boat is accelerated and the force on the oars reaches between 1000 and 1500 N. During the race, the speed is maintained at a lower level with a peak rowing force of 500-700 N for 210-230 strokes for about 6.5 min. Rowers are adapted to this effort by a large muscle mass and high metabolic capacities. The muscles of successful rowers demonstrate 70%-85% slow-tw...

Mammalian skeletal muscles undergo adaptation in response to alteration in functional demands by means of a variety of cellular signaling events. Previous experiments in transgenic mice showed that an active form of Ca2+/calmodulin-dependent protein kinase IV (CaMKIV) is capable of stimulating peroxisome proliferator-activated receptor gamma-coactivator 1alpha (PGC-1alpha) gene expression, prom...

Paralyzed skeletal muscle sometimes becomes faster and more fatigable after spinal cord injury (SCI) because of reduced activity. However, in some cases, pronounced muscle activity in the form of spasticity (hyperreflexia and hypertonus) occurs after long-term SCI. We hypothesized that this spastic activity may be associated with a reversal back to a slower, less fatigable muscle. In adult rats...

abstract         background and objective: scientific evidence reveals that the density of skeletal muscle microcirculations decreases in the patients with chronic heart failure. therefore, this study aimed to determine the impact of submaximal aerobic exercise training on restoration of fast/slow-twitch muscle fibers microcirculation in rats with myocardial infarction.          methods: in thi...

Histochemical differentiation of 12 skeletal muscles with a different fibre type composition was studied in miniature pigs from 80 d of gestation to 1 year of age. Two fetal myofibre types were distinguished at 100 d of gestation by the mATPase reaction after acid preincubation. The staining for oxidative enzyme activities showed no conspicuous differences between fibres up to the 6th day after...