Effects of downhill running incorporated into long-term endurance training on skeletal muscle fiber-type switching and fatigue resistance

The effects of the intermittent incorporation of high-intensity downhill running sessions into long-term endurance training were assessed by examination of the plantaris muscle of rats. First, the intrinsic effects of a single session were evaluated in otherwise sedentary rats. The experimental group showed histological injuries in 2-3 days after the session. In addition, compared with the sedentary control, the experimental group showed a sevenfold increase in the fraction of type IIc fibers, and deceases of 74 and 88% in tetanic force evoked indirectly and directly, respectively, by electric stimulation. The injured muscle fibers showed regeneration within 21 days as evidenced by centrally located nuclei. Next, the effects of intermittently incorporated downhill-running sessions into a 9-week endurance training regimen were tested using two experimental groups: Training and Training + Downhill. On the first day of the 1st, 3rd, 5th, and 7th weeks of the training period, the rats in the Training + Downhill group experienced downhill-running sessions. After the endurance training period, the plantaris muscle of the two experimental groups demonstrated higher fatigue resistance with an increase in the type IIa fiber fraction, at an expense of the type IIb fiber fraction. Compared with the Training group, the Training + Downhill group had a higher type IIa fiber fraction, with clusters of 70-100 type IIa fibers. These results indicate that intermittent high-intensity sessions promote the fiber type transition induced by daily endurance training. However, the potentially adverse effect of fiber type cluster formation suggests that there is an optimum intensity and frequency of the high-intensity exercise sessions for better enhancing the effects of long-term endurance training

Characteristics of the Localization of Connexin 43 in Satellite Cells during Skeletal Muscle Regeneration In Vivo

For myogenesis, new myotubes are formed by the fusion of differentiated myoblasts. In the sequence of events for myotube formation, intercellular communication through gap junctions composed of connexin 43(Cx43) plays critical roles in regulating the alignment and fusion of myoblasts in advances of myotube formation in vitro. On the other hand, the relationship between the expression patterns of Cx43 and the process of myotube formation in satellite cells during muscle regeneration in vivo remains poorly understood. The present study investigated the relationship between Cx43 and satellite cells in muscle regeneration in vivo. The expression of Cx43 was detected in skeletal muscles on day 1 post-muscle injury, but not in control muscles. Interestingly, the expression of Cx43 was not localized on the inside of the basement membrane of myofibers in the regenerating muscles. Moreover, although the clusters of differentiated satellite cells, which represent a more advanced stage of myotube formation, were observed on the inside of the basement membrane of myofibers in regenerating muscles, the expression of Cx43 was not localized in the clusters of these satellite cells. Therefore, in the present study, it was suggested that Cx43 may not directly contribute to muscle regeneration via satellite cells

Upregulation of osteogenic factors induced by high-impact jumping suppresses adipogenesis in marrow but not adipogenic transcription factors in rat tibiae

Jump training is a high-impact training regimen that increases bone volume in young bones. The aim of our study was to determine whether downregulation of adipogenesis that is associated with upregulation of osteogenesis is detected after jump training in growing rat tibiae. Four week-old rats were jump-trained for 1, 2, or 4 weeks for 5 days/week, and the height of jumping progressively increased to 35 cm.We performed morphometry to directly quantitate changes in bone volume and marrow adipocyte distribution in tibiae after the jump training.We also examined changes in expression of osteogenic and adipogenic transcription factor proteins and mRNAs after the jump training. Four weeks of jump training induced an increase in trabecular bone volume, which was associated with recruitment of runt-related transcription factor 2-expressing cells, as well as a decrease in marrow fat volume. However, peroxisome proliferator-activated receptor (PPAR) γ2 protein and mRNA expression levels did not change following high-impact jump training. The mRNA expression levels of the adipocyte differentiation genes CCAAT/enhancer-binding proteins (C/EBP) α, C/EBPβ, and C/EBPδ also showed no change during the training period in jump-trained rats. We suggest that levels of osteogenic factors that were upregulated by mechanical loading from high-impact jumping suppress adipogenesis in marrow rather than adipogenic transcription factors

Age-Related Changes on Morphological and Enzymatic Properties in the Extensor Digitorum Longus Muscle of Senescence Accelerated P6 Mice

Age-related changes on morphological and metabolic properties in the extensor digitorum longus muscle were studied in 20-, 40-, 50-, and 60-week-old female senescence accelerated P6 mice (SAMP6).A decrease in the cross-sectional area of muscle fibers was observed at 50 and 60 weeks of age. However, SDH activity of muscle fibers did not change with aging. These results indicate that the size and SDH activity of muscle fibers in female SAM have different degeneration stages

CHANGES IN ACTIVITIES OF DAILY LIVING,PHYSICAL FITNESS, AND DEPRESSIVE SYMPTOMS AFTER SIX-MONTH PERIODIC WELL-ROUNDED EXERCISE PROGRAMS FOR OLDER ADULTS LIVING IN NURSING HOMES OR SPECIAL NURSING FACILITIES

A 6-month, twice weekly, well-rounded exercise program (47 sessions in total) comprised of a combination of aerobic, resistance and lexibility training was provided for institutionalized older adults aged 60 to 93. We analyzed the data of 18 older adults who could stand and had attended more than 10% of the classes (mean participation rate: 54%) to examine changes in activities of daily living (ADL), physical fitness tests and depressive moods. The mean (± standard deviation, range) age of the participants was 71.3 (±15.6, 60–93) in men and 85.9 (±5.8, 72–93) in women. Significant improvement in ADL of the hand manipulation domain and borderline significant improvement in ADL of the mobility domain were observed (McNemar test p=0.011 and 0.072, respectively). A 6-minute walk distance increased significantly from 151.6 m to 236.6 m (p=0.01, paired t-test), and the result of the Soda Pop test, which tests hand-eye coordination, also improved significantly from 35.2 sec to 25.3 sec (p=0.01, paired t-test). These findings suggest that such a program could be effective in improving the ADL and physical fitness of the elderly