The effects of different patterns of muscle activity on capillary density, mechanical properties and structure of slow and fast rabbit muscles

Abstract

When rabbit fast muscles were chronically stimulated at a frequency naturally occurring in nerves to slow muscles (10 Hz), there was a transformation towards a slow muscle type such as an increase of capillary density, increased activity of the oxidative enzyme, succinic dehydrogenase, and a decrease of muscle fibre diameters. After 28 days the intensity and distribution of SDH and the capillary density were similar to those of soleus. The increases in capillary density preceded the changes in activity of SDH; there was a significantly greater capillary/muscle fibre ratio and number of capillaries/mm2 in muscles stimulated for only 4 days at which time no change could be detected in SDH. These changes were induced by slow frequency stimulation only, and not by an overall increase of activity. Stimulation of fast muscles for 4 days at a higher frequency naturally occurring in the nerves to fast muscles (short bursts of tetani), with the same total number of stimuli as that used in slow frequency stimulation did not produce any changes in capillary density, activity of SDH or contraction times. No changes were observed in either fast or slow muscles stimulated with short bursts of tetani (and lower total number of impulses) up to 28 days. Activation of fast muscles at 5 Hz continuously or 10 Hz intermittently also caused an increase in capillary density. It is therefore concluded that only low frequency activation of fast muscles brings about a transformation of the muscle fibres towards a slow type and that the first noticeable change is an increase in the capillary density.

Selective long-term electrical stimulation of fast glycolytic fibres increases capillary supply but not oxidative enzyme activity in rat skeletal muscles

“…However, using the same stimulation pattern Hudlick a & Tyler (1984) found an increased capillary supply after 14 days. Increases in capillary supply preceding the changes in oxidative enzymes were described previously (Pette et al 1973;Brown et al 1976), and were confirmed more recently (Skorjanc et al 1998) using different stimulation regimes than those used in the present study. It is normally assumed that increased activity of oxidative enzymes in muscles of endurance-trained animals is a sign of hypoxia which triggers capillary growth, possibly via vascular endothelial growth factor (VEGF; Breen et al 1996).…”

“…Physiol. 85.5 Although it is not possible to compare directly results from different species and stimulation regimes, Brown et al (1976) also reported the absence of capillary growth in rabbit muscles using 40 Hz for 4 days, but with a different pattern of stimulation (3 ² 5 s bouts min¢ for 8 h per day) and supramaximal voltage (which activates all muscle fibres). However, using the same stimulation pattern Hudlick a & Tyler (1984) found an increased capillary supply after 14 days.…”

“…Similarly, high-intensity endurance training in animals resulted in increased capillary supply accompanied by increased oxidative capacity (Gute et al 1996). In contrast, chronic electrical stimulation of fast skeletal muscles at a frequency resembling that observed during discharges of slow motoneurons increased capillary supply prior to an increase in the proportion of oxidative fibres (Hudlick a et al 1982) and before any increase in activity of oxidative enzymes (Pette et al 1973;Brown et al 1976), although both parameters were significantly higher than in control muscles after 10-14 days of stimulation (Hudlick a & Tyler, 1984).…”

Functional neuromuscular stimulation in 4 patients with complete paraplegia

“…When the target organ is skeletal muscles, the method is called functional neuromuscular stimulation (FNS) (Peckham, 1981). FNS has been found to increase the capillary density in muscles (Brown et al, 1976) and to increase the skin blood flow (Hellsing, 1986). It also improves the fatigue resistance by increasing the oxidative metabolism in the stimulated muscles (Riley et ai., 1973).…”

O treinamento físico aeróbio corrige a rarefação capilar e as alterações nas proporções dos tipos de fibra muscular esquelética em ratos espontaneamente hipertensos

“…The origin of the transition from type I fibers to type II in soleus muscle of SHR still remains little known; however, studies show it is related to capillary rarefaction followed by alterations in the metabolic properties 11,28 . Studies show that, when there is a transition between the types of fibers of the skeletal muscle, the different morphological properties of the muscular fiber are changed in the following manner: the capillary density and the activities of the enzymes of the energetic metabolism are early altered during the transition and precede the change in the activity of the myofibrillar ATPase and the contractile characteristics of the muscle 8,29 . In mammals, the fibers of the skeletal muscle are usually classified in type I and type II fiber according to the different activities of the myosin ATPase after the pre-incubation in different pHs, and the type II fibers can be subclassified in IIA, IIX/D and IIB.…”