Effect of exercise on muscle fibre composition and enzyme activities of skeletal muscles in young rats.

Young Wistar rats underwent dynamic (D) or static (S) exercise from the 5th to 35th day after birth. Histochemical and biochemical analysis were performed in the extensor digitorum longus (EDL) and the soleus muscle (SOL). Lactate dehydrogenase (LDH) (regulating anaerobic metabolism) and citrate synthase (CS) and hydroxyacyl-CoA dehydrogenase (HAD) (both regulating aerobic metabolism) activities were determined spectrophotometrically. An increase of the fast oxidative-glycolytic (FOG) muscle fibres was found in the slow SOL muscle in both trained groups, i.e. by 10% in group D and by 7% in group S in comparison with the C group. The EDL muscle fibre distribution did not differ from those of control animals in respect to the slow oxidative (SO) fibre type. A higher percentage of FOG fibres by 19% was found in group D contrary to a decreased number of the fast glycolytic (FG) muscle fibres in this trained group. The greatest increase of CS (EDL 185%, SOL 176%) and HAD (EDL 83%, SOL 178%) activities were found in group D as compared with control group (C). Only small differences were observed in LDH activity. The values of characteristic enzyme activity ratios show that dynamic training resulted in an elevation of oxidative capacity of skeletal muscle, while the static load led preferentially along the glycolytic pathway. It may be concluded that an adaptive response to the training load during early postnatal development is different due to the type of exercise (dynamic or static) and/or the type of skeletal muscle (fast or slow).

Skeletal muscle characteristics of sprint cyclists and nonathletes.

Muscle fiber distribution and muscle enzyme activity (m. vastus lat.) were investigated in 10 elite sprint cyclists and 12 nonathletes. The ratio of fast to slow muscle fibers was 2:3 in cyclists and 3:2 in nonathletes. The mean diameter of each muscle fiber type was significantly higher in the athletes. The mean enzyme activity values in mu kat X g-1 w.w. for cyclists and nonathletes, respectively, were as follows: triosephosphate dehydrogenase (TPDH), 6.2 and 3.78; lactate dehydrogenase (LDH), 4.4 and 4.59; citrate synthase (CS), 0.154 and 0.13; hydroxyacyl-CoA dehydrogenase (HAD), 0.041 and 0.07. The mean difference between groups in TPDH and in (TPDH + LDH)/(CS + HAD) ratio were statistically significant. Maximum voluntary isometric strength (knee extension) was about 17% greater in cyclists than the mean value for Czechoslovakian men of the same age. A strong positive correlation (r = 0.72) between the percent of fast glycolytic fibers (type II B) and isometric strength was observed in the cyclists. Furthermore, mean weight-compensated maximal oxygen consumption (VO2 max, ml X kg-1 X min-1) for all subjects (n = 22) was significantly related to percent of slow oxidative fibers (type I) (r = 0.75) and to the mean diameter of type II B (r = 0.58), fast oxidative-glycolytic fibers (type II A) (r = 0.68) and type I fibers (r = 0.59).

Effects of postnatal influences on conditioning and some functional and structural brain parameters in rats.

Early postnatal influences were studied in rats in three different ways: (i) different litter size, (ii) feeding with restricted amount of protein, (iii) different level of afferent stimulation. A complex evaluation of spontaneous activity, conditioning, electrophysiological and biochemical analyses was used in these experiments. Medium sized litters showed the greater electrophysiological reactivity (cortical evoked potentials) and the most stable performance in different kinds of conditioning (avoidance) experiments. Animals reared on a low protein diet were subnormal in electrophysiological indices, and had a lower level of biochemical activity for materials Involved in neural excitability, electrogenesis, and cellular and subcellular energetic metabolism (phospholipids, proteins, DNA, RNA). In all respects (behavioral, electrophysiological and biochemical tests) animals with partial sensory deprivation in the postnatal period had the lowest indices. The "stimulated" animals on the other hand were superior to both other groups in the tests used for the analysis of higher nervous activity, but electrophysiological and biochemical analyses did not show clear differences between the "stimulated" and control animals. Optimal development of brain functions requires adequate conditions in the early postnatal period. However, the "adequacy" of them conditions has dill to be determined more precisely.