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Bone loss in the lower leg during 35 days of bed rest is predominantly from the cortical compartment
Joern Rittweger, Boštjan Šimunič, Giancarlo Bilancio, Natale Gaspare De Santo, Massimo Cirillo, Gianni Biolo, Rado Pišot, Ola Eiken, Igor B. Mekjavić, Marco Narici, 2009, original scientific article

Abstract: Immobilization-induced bone loss is usually greater in the epiphyses than in the diaphyses. The larger fraction of trabecular bone in the epiphyses than in the diaphyses offers an intuitive explanation to account for this phenomenon. However, recent evidence contradicts this notion and suggests that immobilization-induced bone loss from the distal tibia epiphysis is mainly from the cortical compartment. The aim of this study was to establish whether this pattern of bone loss was a general rule during immobilization. Wemonitored various skeletal sites with different tissue composition during 5 weeks of immobilization. Ten healthy male volunteers with mean age of 24.3 years (SD 2.6 years) underwent strict horizontal bed rest. Bone scans were obtained during baseline data collection, at the end of bed rest and after 14 days of recovery by peripheral Quantitative Computed Tomography (pQCT). Sectional images were obtained from the distal tibia epiphysis (at 4% of the tibia's length), from the diaphysis (at 38%), from the proximal metaphysis (at 93%) and from the proximal epiphysis (at 98%), as well as from the distal femur epiphysis (at 4% of the femur's length) and from the patella. Relative bone losses were largest at the patella, where they amounted to - 3.2% (SD 1.8%, p < 0.001) of the baseline values, and smallest at the tibia diaphysis, where they amounted to - 0.7% (SD 1.0%, p = 0.019). The relative losses were generally larger from cortical than from trabecular compartments (p = 0.004), and whilst all skeletal sites depicted such cortical losses, substantial trabecular losses were found only from the proximal tibia epiphysis. Results confirm that the differential losses from the various skeletal sites cannot be explained on the basis of trabecular vs. cortical tissue composition differences, but that endocortical circumference can account for the different amounts of bone loss in the tibia. The present study therefore supports the suggestion of the subendocortical layer as a transitional zone, which can readily be transformed into trabecular bone in response to immobilization. The latter will lead to cortical thinning, a factor that has been associated with the risk of fracture and with osteoarthritis.
Found in: osebi
Keywords: space flight, simulated microgravity, osteoporosis, exercise, pQCT
Published: 15.10.2013; Views: 2035; Downloads: 51
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Effects of inactivity on human muscle glutathione synthesis by a double-tracer and single-biopsy approach
Francesco Agostini, Luciano Dalla Libera, Joern Rittweger, Sara Mazzucco, Mihaela Jurdana, Igor B. Mekjavić, Rado Pišot, Luisa Gorza, Marco Narici, Gianni Biolo, 2010, original scientific article

Abstract: Oxidative stress is often associated to inactivity-mediated skeletal muscle atrophy. Glutathione is one of the major antioxidant system stimulated, both at muscular and systemic level, by activation of oxidative processes. We measured changes in glutathione availability, oxidative stress induction and atrophy extent mediated by 35-days of experimental bed rest in vastus lateralis muscle of healthy human volunteers. To assess muscle glutathione synthesis, we applied a novel single-biopsy and double-tracer ([2H2]glycine and [15N]glycine) approach based on evaluation of steady-state precursor incorporation in product. The correlations between the traditional (multiple-samples, one-tracer) and new (one-sample, double-tracer infusion) methods were analyzed in erythrocytes by Passing & Bablok and Altman-Bland tests. Muscle glutathione absolute synthesis rate increased following bed rest from 5.5 1.1 to 11.0 1.5 mmol (kg wet tissue / day)-1 (n=9; p=0.02) while glutathione concentration failed to change significantly. Bed rest induced vastus lateralis muscle atrophy, as assessed by pennation angle changes measured by ultrasonography (from 18.6 1.0 to 15.3 0.9 degrees; p=0.01) and thickness changes (from 2.3 0.2 to 1.9 0.1 cm; p<0.001). Moreover, bed rest increased protein oxidative stress, as measured by muscle protein carbonylation changes (from 0.6 0.1 to 1.00 0.1 Oxy RP-1; p<0.04). In conclusion, we developed in erythrocytes a new minimally-invasive method to determine peptide synthesis rate in human tissues. Application of the new method to skeletal muscle suggests that disuse atrophy is associated to oxidative stress induction as well as to compensatory activation of the glutathione system
Found in: osebi
Keywords: Antioxidant system, Muscle damage, Oxidative stress, bed rest, muscle glutathione, stable isotopes
Published: 15.10.2013; Views: 2081; Downloads: 80
URL Full text (0,00 KB)

Skeletal muscle oxidative function in vivo and ex vivo in athletes with marked hypertrophy from resistance training
Desy Salvadego, R. Domenis, Stefano Lazzer, Simone Porcelli, Joern Rittweger, Giovanna Rizzo, I. Mavelli, Boštjan Šimunič, Rado Pišot, Bruno Grassi, 2013, original scientific article

Abstract: Oxidative function during exercise was evaluated in 11 young athletes with marked skeletal muscle hypertrophy induced by long-term resistance training (RTA, body mass 102.67.3 kg, meanSD) and 11 controls (CTRL, body mass 77.86.0). Pulmonary O2 uptake (V'O2) and vastus lateralis muscle fractional O2 extraction (by near-infrared spectroscopy) were determined during an incremental cycle ergometer (CE) and one-leg knee-extension (KE) exercise. Mitochondrial respiration was evaluated ex vivo by high-resolution respirometry in permeabilized vastus lateralis fibers obtained by biopsy. Quadriceps femoris muscle cross sectional area, volume (determined by magnetic resonance imaging) and strength were greater in RTA vs. CTRL (by ~40%, ~33% and ~20%, respectively). V'O2peak during CE was higher in RTA vs. CTRL (4.050.64 L min-1 vs. 3.560.30); no difference between groups was observed during KE. The O2 cost of CE exercise was not different between groups. When divided per muscle mass (for CE) or quadriceps muscle mass (for KE) V'O2peak was lower (by 15-20%) in RTA vs. CTRL. Vastus lateralis fractional O2 extraction was lower in RTA vs. CTRL at all work rates, both during CE and KE. RTA had higher ADP-stimulated mitochondrial respiration (56.723.7 pmolO2s-1mg-1 ww) vs. CTRL (35.710.2), and a tighter coupling of oxidative phosphorylation. In RTA the greater muscle mass and maximal force, and the enhanced mitochondrial respiration seem to compensate for the hypertrophy-induced impaired peripheral O2 diffusion. The net results are an enhanced whole body oxidative function at peak exercise, and unchanged efficiency and O2 cost at submaximal exercise, despite a much greater body mass
Found in: osebi
Keywords: skeletal muscle, hypertrophy, mitochondrial respiration, oxidative metabolism, exercise
Published: 15.10.2013; Views: 2048; Downloads: 58
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Odziv sestave telesa, mišične togosti in ravnotežja po 35-dnevni odsotnosti gibanja pri mladih in zdravih preiskovancih
Boštjan Šimunič, Joern Rittweger, Gregor Cankar, Mihaela Jurdana, Tadeja Volmut, Tina Šetina, Igor B. Mekjavić, Rado Pišot, 2008, original scientific article

Abstract: Uvod: Problemi sedečega načina sodobnega življenja se kažejo v fizioloških odzivih, tako pri starejših kot tudi pri mlajših ljudeh. Cilj raziskave je bilugotoviti odziv morfoloških in skeletno-mišičnih značilnosti ter izgubo funkcionalnih sposobnosti ohranjanja ravnotežja po 35-dnevni popolni gibalni nedejavnosti in zagotovljeni uravnoteženi prehrani glede na njeno sestavo in preiskovančevo telesno težo. Metode: Deset moških preiskovancev (starih 24,32,6 let) je v bolnišničnem okolju preležalo 35 dni v vodoravnem položaju. Fiziološke odzive telesa smo vrednotili z merjenji telesne, maščobne in mišične mase, mineralne vsebnosti sprednje golenske kosti, togosti trebuha dveh funkcionalno različnih glav antigravitacijske mišice in sposobnost ohranjanja ravnotežja. Rezultati: Preiskovanci so v povprečju značilno izgubili 0,97 % (P=0,001) telesne teže, 4,1 % (P=0,009) mišične mase in 1,7 % (P=0,000) mineralne gostote tibialne kosti ter pridobili 1,4 % (P<0,000) maščobne mase. Mišična togost se je značilno zmanjšala od 8. dne ležanja (P=0,006) dalje pri distalni in že od 1. dneva (P=0,007) dalje pri proksimalniglavi notranje stegenske mišice ter se 14. dan po zaključku BR vrnila v izhodiščno stanje le pri distalni glavi. Po zaključku BR in dan kasneje smo ugotovili značilno izgubo ohranjanja ravnotežja za 9,5 % (P=0,006), in 17,4 % (P=0,000), medtem ko 14. dan po zaključku ležanja ni biloveč značilnih razlik. Zaključek: Povzamemo lahko, da z uravnoteženo prehrano lahko omejimo izgubo telesne teže in pridobivanje maščobne mase, vendar ne moremo zmanjšati izgube mišične mase ter mineralne vsebnosti tibialne kosti. Ugotovili smo, da se mišična togost zmanjšuje v dveh časovno zakasnjenih procesih. Sposobnost ohranjanja ravnotežja je zmanjšana v vsaj prvih 24 urah po zaključku ležanja.
Found in: osebi
Keywords: popolna gibalna neaktivnost, okoljska fiziologija, tenziomiografija, ravnotežje, morfologija, kostna mineralna vsebnost, mišična togost
Published: 15.10.2013; Views: 2202; Downloads: 38
URL Full text (0,00 KB)

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