Effects of low-frequency electrical stimulation, which is currently considered to be a possible countermeasure for long-duration spaceflights, with and without stretch were evaluated. Twelve young male volunteers were randomly distributed into two groups. In one group anterior thigh muscles—knee extensors of both legs were stimulated with frequency of 15 Hz for 4.5 wks, six times a week; each session was 6-h long. In the other group, electrical stimulation with the same parameters was applied to stretched knee extensors. Following stimulation the subjects exhibited an increase in fatigue resistance, and in the succinate dehydrogenase activity and a 10% gain in the percentage of muscle fibers with slow myosin heavy chain isoforms. In a stimulated group the peak voluntary strength went down significantly, the CSA of fast muscle fibers in m. quadriceps femoris became slightly less in size (10%). Electrical stimulation of the stretched muscles induced an insignificant decline in their strength and an increase of cross-sectional area of muscle fibers of both types. Thus chronic low-frequency electrical stimulation may be proposed as a candidate countermeasure against muscle strength and mass loss if it is combined with stretch.

Peroxisome proliferator-activated receptor α (PPARα) regulates genes responsible for skeletal and heart muscle fatty acid oxidation. Previous studies have shown that the PPARα intron 7 G/C polymorphism was associated with left ventricular growth in response to exercise. We speculated that GG homozygotes should be more prevalent within a group of endurance-oriented athletes, have normal fatty acid metabolism, and increased percentages of slow-twitch fibers. We have tested this hypothesis in the study of a mixed cohort of 786 Russian athletes in 13 different sporting disciplines prospectively stratified by performance (endurance-oriented athletes, power-oriented athletes and athletes with mixed endurance/power activity). PPARα intron 7 genotype and allele frequencies were compared to 1,242 controls. We found an increasing linear trend of C allele with increasing anaerobic component of physical performance (P=0.029). GG genotype frequencies in endurance-oriented and power-oriented athletes were 80.3 and 50.6%, respectively, and were significantly (P<0.0001) different compared to controls (70.0%). To examine the association between PPARα gene variant and fiber type composition, muscle biopsies from m. vastus lateralis were obtained and analyzed in 40 young men. GG homozygotes (n=25) had significantly (P=0.003) higher percentages of slow-twitch fibers (55.5±2.0 vs 38.5±2.3%) than CC homozygotes (n=4). In conclusion, PPARα intron 7 G/C polymorphism was associated with physical performance in Russian athletes, and this may be explained, in part, by the association between PPARα genotype and muscle fiber type composition.

The study investigated the effects of chronic low-frequency electrical stimulation (CLFES) of the stretched knee extensor muscles versus CLFES without a resistance load. A total of 19 male volunteers were randomized into two groups with similar aerobic and force-velocity properties. In group 1, anterior thigh muscles (the knee extensors) of both legs were exposed to CLFES (15 Hz). In group 2, the CLFES of the knee extensors was combined with stretching. The stimulated subjects demonstrated a marked tendency towards increasing endurance and a significant increase (by 10%) in both succinate dehydrogenase activity and the percentage of muscle fibers containing slow myosin heavy chain (MHC) isoforms. At the same time, the proportion of fibers reacting with the antibody against fast MHC isoforms decreased by 12%. In group 1, the maximum voluntary force (MVF) significantly decreased, the volume of m. quadriceps femoris (as measured by magnetic resonance imaging) remained unchanged, and the size of the fast fibers slightly decreased (by 11%). In group 2, no significant decrease in the MVF was observed, while there was a significant increase in muscle volume and the cross-sectional area of muscle fibers.

Effect of functional unloading on the course of degenerative process in muscles was studied in dystrophin-deficient mdx mice. Head down-hanging of animals led to a significant decrease in the cross-section area of muscle fibers, increase in the percentage of fibers with centrally located nuclei and of Evans blue-stained fibers. Gravitation unloading of 12-month-old animals with pronounced manifestations of muscular dystrophy did not inhibit this pathological process.