Effects of speed training on the fibre composition of the longissimus lumbaris muscle.

Thirty-six adult male and female Wistar rats were divided into three groups, each of which underwent different training programmes in which greater relevance was attached to the intensity of exercise than to its duration. Samples of the longissimus lumbaris muscle taken between the second and fourth lumbar vertebra, were stained with m-ATPase after acid preincubation at pH 4.4, and with NADH-TR. The most notable results obtained were: (a) none of the training programmes involved gave rise to changes in the ratio of type I: type II fibres; (b) the proportion of IIA fibres increased in all cases, while the proportion of IIB fibres decreased correspondingly; (c) the percentage of FT fibres decreased significantly, and in greater proportion than the decrease recorded in IIb fibres, and (d) specific speed training schedules led to greater changes in the fibre composition of this muscle.

Muscle fibre type composition in untrained and endurance-trained Andalusian and Arab horses.

Muscle biopsies were taken from the middle gluteal muscle of 68 stallions (52 Andalusian [AN] and 16 Arab [AR]) ranging from six to 12 years of age. Seventeen AN horses and eight AR horses were untrained, while the remainder underwent active endurance training for 6 months. Fifteen AN horses were moderately endurance-trained while the other 20 AN horses and eight AR horses were strongly endurance-trained. Percentages of type I and type II fibres were similar in all groups (P greater than 0.05). The group of horses with the hardest training had a higher percentage of type IIA fibres (AN P less than 0.01; AR P less than 0.02) and a lower percentage of type IIB fibres (P less than 0.05 for AN and AR) than the untrained horses. All trained horses had a higher percentage of type IIB oxidative fibres and a lower percentage of type IIB non-oxidative fibres than the untrained horses (P less than 0.01 for both). These results suggest that the proportions of type I and type II fibres are highly stable within a given breed, but the stimulus of training facilitates changes both in contractile properties and, particularly, in the oxidative capacity of type II subgroups.

[Adaptation of the fibrillar composition of the lumbar longissimus muscle to resistance training]. / Adaptaciones en la composición fibrilar del músculo longisimo lumbar a entrenamientos de resistencia.

The effect of exercise training on the longissimus muscle types was investigated in rats. There were four groups of rats, each exposed to exercise of equal intensity, but of varying duration. A segment of the longissimus muscle between the 2nd and 4th lumbar vertebrae was used for muscle fiber classification with histochemical ATPase classification. With exercise there were no significant changes in the percentage of the muscle comprised of type I muscle fibers. There was, however, significant increase in the percentage of type II A fibers. This paralleled a decrease in type II B fibers. The percentage of FG fiber types decreased significantly in all groups studied. There was a correlation between intensity and duration of exercise and the degree of decrease seen in the latter fiber types. An increase in oxidative muscle capabilities was evidence by the changes observed in the subtypes of class II fibers.

Variations in fibre composition of the gastrocnemius muscle in rats subjected to speed training.

Thirty-six adult Wistar rats were divided into three groups. One group was used as a control, and the other two underwent different training programmes in which greater relevance was attached to the intensity of exercise than to its duration. Samples of the red and mixed portions of m. gastrocnemius (caput lateralis) were stained with m-ATPase to determine the percentage of type I, IIA and IIB fibres, and with NADH-TR in order to quantify variations in the percentage of low staining intensity (FG) fibres. The most notable results obtained were: a) the ratio of type I type II fibres remained unchanged; b) the proportion of IIA fibres increased, while that of IIB fibres decreased correspondingly; c) FG fibres, which were virtually absent from the red portion, recorded a clear decrease which was more marked, and occurred more rapidly, than in IIB fibres. These differences were all statistically significant in the mixed portion of the muscle. Adaptive changes in fibre composition in the red portion were less marked.

Type IIC fibres in certain muscles of the adult rat (sedentary and exercised).

Samples were taken, at fixed levels, of the vastus lateralis, the caput lateralis of the gastrocnemius muscle and the longissimus lumbaris of 72 Wistar rats which were either sedentary or subjected to various exercise schedules. The samples were analyzed using the histochemical technique of myosin ATPase (m-ATPase) after preincubation at pH 4.2, and the fibre-types I, II (IIA and IIB) and IIC were identified, calculating the percentage of type IIC fibres as well as their minimum diameter. The percentages of these IIC fibres found in the red and mixed parts of the gastrocnemius (caput lateralis) and the longissimus lumbaris were between 0.7% and 2.6%. However, their presence was not detected in the vastus lateralis or in the white part of the gastrocnemius (caput lateralis). The lack of differences in this fibre type between the males and females of the population was shown statistically. Likewise, no significant modification of the IIC fibres between sedentary and exercised animals was seen. With regard to fibrillar size, females showed a smaller minimum diameter than males, the results showing a small increase in the size of these fibres in both sexes after exercise, although in most cases this was not statistically significant.

Degree of correspondence between contractile and oxidative capacities in horse muscle fibres: a histochemical study.

Samples taken from the middle gluteal muscle of 95 untrained adult horses of different ages and sex were subjected to histochemical analysis using the myosin adenosine triphosphatase (m-ATPase) and nicotinamide adenine dinucleotide tetrazolium reductase (NADH-TR) staining techniques. Fibres were classified into types I, IIA and IIB according to m-ATPase activity after preincubation at pH 4.4. The percentage of FT (Fast-Twitch Glycolytic) fibres and the proportion of IIB fibres with "high" and "low" oxidative capacity were determined in serial sections stained for NADH-TR. Statistical analysis revealed a significantly higher proportion of IIB fibres than FT fibres (P less than 0.001), though both percentages were correlated. Thus, 72.2 +/- 17.6% of type IIB fibres showed low oxidative capacity, but the remaining 27.8 +/- 17.6% showed high aerobic potential, and thus did not correspond to FT fibres. These results confirm that the contractile capacity of a muscle fibre does not determine its oxidative profile. The different types of muscle fibre should thus be classified solely according to m-ATPase activity, since this characteristic is related to the molecular structure of contractile proteins. Oxidative capacity should be assessed separately, and not be used as a criterion for fibre classification in horses.

Variations in fibre size in the gastrocnemius muscle of rats undergoing training.

Sixty-six Wistar rats of both sexes were divided into six groups. One group was used as control, and the others underwent different training schedules. Muscle samples taken from the red and mixed portions of m. Gastrocnemius (caput lateralis) were stained with m-ATPase in order to identify fibre types I, IIA and IIB. These fibres were measured in order to determine their minimum diameter. The most notable results obtained were: a) the three types of fibre were generally larger in males than in females; b) the mean minimum diameter of fibres from the mixed portion was smaller than those of the red portion, except type IIB fibres, and c) the training schedules involved generally led to slight hypertrophy of all types of fibres, although this finding was more significant in the mixed portion of m. Gastrocnemius.

Effects of training on fibre composition in rat gastrocnemius muscle.

Forty-eight adult Wistar rats were divided into four groups for experimentation. The group I was used as a control and groups II, III and IV underwent progressive treadmill training. Samples of the red and mixed portions of m. gastrocnemius (lateral head) were stained with the histochemical technique of m-ATPase to determine the percentage of type I, IIA and IIB fibres, and with NADH-TR, in order to quantify variations in "low-oxidative" fibre percentages. The results showed that progressive training did not lead to statistical variations in the percentage of type I fibres. However, the proportion of type IIA fibres rose, while that of IIB fibres fell, in both cases significantly. Variations were more marked in mixed than in red Gastrocnemius muscle. A clear decrease was noted in "low-oxidative" fibres, which were virtually absent from red portion. This decrease was more marked, and occurred more rapidly, than in type IIB fibres.