104,962 research outputs found
Muscle tissue adaptations of highlanders to training in chronic hypoxia or acute normoxia.
No full textTwenty healthy high-altitude natives, residents of La Paz, Bolivia (3,600 m), participated in 6 wk of endurance exercise training on bicycle ergometers, 5 times/wk, 30 min/session, as previously described in normoxia- trained sea-level natives (H. Hoppeler, H. Howald, K. E. Conley, S. L. Lindstedt, H. Claassen, P. Vock, and E. R. Weibel. J. Appl. Physiol. 59: 320- 327, 1985). A first group of 10 subjects was trained in chronic hypoxia (HT; barometric pressure = 500 mmHg; inspired O2 fraction = 0.209); a second group of 10 subjects was trained in acute normoxia (NT; barometric pressure 500 mmHg; inspired O2 fraction = 0.314). The workloads were adjusted to ~70% of peak O2 consumption (V̇O2(peak)) measured either in hypoxia for the HT group or in normoxia for the NT group. (V̇O(2peak)) determination and biopsies of the vastus lateralis muscle were taken before and after the training program. (V̇O(2peak)) in the HT group was increased (14%) in a way similar to that in NT sea-level natives with the same protocol. Moreover, (V̇O(2peak)) in the NT group was not further increased by additional O2 delivery during the training session. HT or NT induced similar increases in muscle capillary-to-fiber ratio (26%) and capillary density (19%) as well as in the volume density of total mitochondria and citrate synthase activity (45%). It is concluded that high-altitude natives have a reduced capillarity and muscle tissue oxidative capacity; however, their training response is similar to that of sea-level residents, independent of whether training is carried out in hypobaric hypoxia or hypobaric normoxia
Effects of bedrest on deltoideus muscle morphology and enzymes
No full textTo examine the effects of unweighting on the structural and metabolic adaptations of a non-postural muscle, deltoideus muscle biopsies were taken in seven male healthy subjects, before and after a 37 day bedrest. Myofibrillar ATPase histochemistry demonstrated no change in fibre type distributions (I, IIA, IIB), in fibre cross-sectional areas nor in capillary supply. No difference was noted in enzyme activities of oxidative metabolism (citrate synthase, 3-hydroxy-acyl-CoA dehydrogenase), and glycolysis (hexokinase, lactate dehydrogenase). Electron microscopy showed a decrease in the volume density of lipids but no change in mitochondrial volume density and distribution. The results indicate that bedrest induces no major morphological and biochemical changes in deltoideus muscle, contrary to what was previously reported in vastus lateralis muscle. This lack of changes is probably related to an unaltered deltoideus muscle use
Muscle unloading potentiates the effects of acetyl-L-carnitine on the slow oxidative muscle phenotype
No full textThe effect of acetyl-L-carnitine (ALCAR) supplementation to 3-month-old rats in normal-loading and unloading conditions has been here investigated by a combined morphological, biochemical and transcriptional approach to test whether ALCAR might cause a remodeling of the metabolic/contractile phenotype of soleus muscle. Morphological assessment demonstrated an increase of type I oxidative fiber content and cross-sectional area in ALCAR-treated animals both in normal-loading and in unloading conditions. ALCAR prevented loss of mitochondrial mass in unloaded animals whereas no ALCAR-dependent increase of mitochondrial mass occurred in normal-loaded muscle. Validated microarray analysis delineated an ALCAR-induced maintenance of a slow-oxidative expression program only in unloaded soleus muscle. Indeed, the muscle adjustment of the expression profile of factors underlying mitochondrial oxidative metabolism, protein turnover, fiber type differentiation and an adaptation of voltage-gated ion channel expression was distinguishable with respect to the loading status. This selectivity may suggest a key role of muscle loading status in the manifestation of ALCAR effects. The results extend to a broader level of biological informations the previous notion on ALCAR positive effect in rat soleus muscle during unloading and point to a role of ALCAR for the maintenance of its slow-oxidative fiber character
Maximal exercise performance in chronic hypoxia and acute normoxia in high altitude natives.
No full text
Exercise training in chronic hypoxia has no effect on ventilatory muscle function in humans.
No full textEffects of endurance training on oxidative capacity and structural composition of human arm and leg muscles
No full textSix healthy subjects performed endurance training of the same duration with legs and arms consecutively. Performance and muscle structure were measured before and after training in lower and upper limbs. Training induced similar increases in maximal oxygen consumption (6 ± 1 vs. 7 ± 2 mL min-1 kg-1: legs vs. arms, P > 0.05) and mitochondrial volume in leg and arm muscles (42 ± 12 vs. 31 ± 11%: legs vs. arms, P > 0.05). The gain in mitochondrial volume after training was achieved solely by increasing the fraction of mitochondria (+40 ± 11%, P > 0.05) in the same muscle volume (+2 ± 2%, P > 0.05) in the legs. In contrast, increased muscle volume (+14 ± 3%, P 0.05), occurred in the arms after training. Thus, similar improvements in muscle oxidative capacity in upper and lower limbs were brought about by different mechanisms. It is suggested that due to infrequent use and a lack of load-bearing function, arm muscle volume is underdeveloped in untrained, sedentary or detrained/injured subjects and that the mode of endurance training used in this study is sufficient to enlarge arm muscle volume as well as aerobic capacity
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