Effect of hyperbaric oxygenation on maximal aerobic performance in a normobaric environment.

Eighteen female physical education students, randomly divided into three groups, inhaled 100% O2 for 60 minutes in a hyperbaric chamber. Pressure in the chamber amounted to 2.8 ATA. Three days before the hyperbaric oxygenation (HBO) all the students were subjected to a treadmill test. The first group was retested after 30 minutes, the second after 3 hours and the third 6 hours after the HBO. The first and the second groups of subjects achieved statistically significant maximal oxygen consumption after the HBO (14.4 and 10% respectively) and were capable of sustaining considerably higher exertion on treadmill (12.8%, namely 18.1%, both values were significant on the level of p less than 0.05). The ventilation efficiency parameters (VEO2 and R) did not differ with any of the three groups of subject during the exertion before and after the HBO, although after the HBO the exertion was considerably higher.

Fine structural changes in electrostimulated human skeletal muscle. Evidence for predominant effects on fast muscle fibres.

Physical education students were subjected to electrical stimulation of relatively high frequency and current amplitude for 19 days. A quantitative study of several morphological parameters was performed on biopsy samples from gastrocnemius, using stereological methods at both light and electron microscopic levels. The main results were: muscle fibre size was increased; nuclear volume was also increased, suggesting that a proliferation of nuclei had occurred; this was paralleled by an increased content of nuclear DNA. The size of single myonuclei was increased, and their heterochromatin fraction was decreased, these changes being most pronounced in type II fibres. The increase in the mitochondrial fraction was also greatest in type II fibres. It is concluded that this type of electrical stimulation has predominant effects on type II fibres.

Effects of electrical stimulation of different frequencies on the myonuclei and fiber size in human muscle.

Male physical education students were subjected to electrical stimulation for a period of 21 days. The stimulation was performed with alternating currents of rectangular wave form. Group I was stimulated with a frequency of 50 Hz, group II with a frequency of 2000 Hz. Before and after the experimental period, biopsies were taken from the m. gastrocnemius. The muscle fiber size and the number and size of nuclei was estimated at the light microscopic level using stereological methods. The fiber size was significantly increased only in group I. The nuclear number and the nuclear size increased significantly in both groups leading to a higher nuclear volume per unit tissue volume. It was assumed that the proliferation of nuclei is correlated to satellite cell proliferation resulting probably in hypertrophy or hyperplasia of electrostimulated skeletal muscle.

Stereological analysis of capillaries in electrostimulated human muscles.

The effects of two methods of electrical stimulation on the capillary density in skeletal muscle was studied. Twenty-two male physical education students randomly divided into two groups participated in the experiment. Groups I and II were subjected to the procedure of electrical stimulation of m. triceps surae daily for a period of 21 days. Group I was stimulated by an alternating current of relatively low frequency (50 Hz), and group II was stimulated by an alternating current of relatively high frequency (2000 Hz). Biopsy specimens were obtained from the lateral portion of m. gastrocnemius 1 week before the stimulation and 1 day after the completion of the stimulation period. The capillary network was analyzed using morphometric and stereological techniques. Significant changes were found for capillary number in cross section, capillary density, intercapillary distance, tissue cylinder corresponding to one capillary (Krogh's cylinder) in both groups, and for capillary number-to-fiber area ratio in group I. Differences between the results of groups I and II were not significant in any cases. The changes observed speak in favor of an improved capillary supply to skeletal muscle after electrical stimulation.

Effect of electrical stimulation of high and low frequency on maximum isometric force and some morphological characteristics in men.

The effects of two methods of electrical stimulation on maximum isometric force, calf girth, and skinfold thickness of stimulated and nonstimulated (contralateral) legs were studied. Thirty-six male volunteers, divided into three groups, participated in the experiment. Groups I and II were subjected to the procedure of electrical stimulation of m. triceps surae daily for a period of 21 days. Group I was stimulated by an alternating current of low frequency (50 Hz); group II was also stimulated by an alternating current but of higher frequency (2000 Hz). Group III served as control group. In groups I and II significant increases of the maximum isometric force (as measured on an electronic dynamometer) of the stimulated (50.3% and 58.8%) and also of the nonstimulated (contralateral) muscles (39.7% and 32.2%) were found. In group III no significant increase of the maximum isometric force was registered. After the period of stimulation, the skinfold thickness was notably reduced by 21.6% in group II, and calf girth was enlarged in both experimental groups. Relatively large changes were realized in the calf girth and the skin-fold thickness of the nonstimulated legs. The changes in group III were insignificant. It is concluded that electrical stimulation with low as well as high frequencies exerts great effects on muscle force.

Morphometric analyses on the muscles of exercise trained and untrained dogs.

Nine adult dogs were subjected to an endurance training program consisting of gradually increasing periods of treadmill exercise. Biopsies of vastus lateralis muscles taken prior to an on completion of the training program were used to study the alterations in the capillary network and muscle-fiber nuclei. Combined morphometric and stereological analyses showed that the total length of capillaries (LV) and their total surface area (SV) per unit volume of muscle was significantly increased during training. Changes in the properties of myonuclei following training were also studied. Highly significant increases in the number of nuclei per unit volume of muscle (NV) were found. The increase in the numerical density of muscle-fiber nuclei would seem to indicate that the new nuclei were formed in the muscle during prolonged training. The relative amounts and distribution of heterochromatin and euchromatin were measured in trained and untrained dogs using a simple point-counting and random-transect technique. Their content of the different types of chromatin (volume functions and chromatin patch sizes in micrographs) were found to be altered significantly as a result of the training. The findings were consistent with the view that the amount of euchromatin within nuclei varies according to the degree of cellular activity.

Stereological analyses of capillaries in muscles of dystrophic mice.

Stereological analyses of the distribution of capillaries in skeletal muscles of congenitally dystrophic mice are described and reported. Two methods are used, each based on a different mathematical model of the 3-dimensional distribution of lines in space. For these analyses specimens of extensor digitorum longus muscle from clinically affected C57BL/6Jdy2J/dy2J dystrophic mice, and from non-littermate controls, were used. The analyses were carried out on transverse and longitudinally orientated semithin sections of these muscles. Although the two methods employed are based on different mathematical models and yield results relevant to each particular model, it is clear that there is a more extensive capillary network present per unit volume of the dystrophic muscle than in control muscles. These findings are relevant to the theories which involve a vascular aetiology for muscular dystrophy. It is apparent that, in order to explore the structure of the capillary network more fully, there is a need for the development of more sophisticated stereological techniques for analysis of capillaries in skeletal muscle.

Quantitative studies on the numerical frequency of myonuclei in the muscles of exercised rats: evidence against the occurrence of fibre-splitting.

The histological changes associated with exercise-induced muscular hypertrophy have variously been interpreted as due to fibre-splitting or satellite-cell activity. If due to fibre-splitting, than a marked fall in the number of nuclei per unit volume of muscle must occur. To see if this is the case, we have examined post-mortem specimens of extensor digitorum longus muscles in rats exercised by swimming for up to 30 min twice daily for 35 days. The mean cross-sectional area of muscle fibres was unaltered by exercise but mean length of capillary per unit volume of muscle was increased by 55% and number of nuclei per unit volume of muscle by 30%, both changes being significant. Mean nuclear volume increased by approximately 75%. Thus the muscles did adapt to exercise and new myonuclei were formed, contrary to expectations if fibre-splitting were the essential change. In this study the fibres seemed not to have increased in size and further studies, perhaps using autoradiographic analysis of tritiated thymidine-labelled satellite-cell nuclei, are needed to clarify the precise mechanisms involved.