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1.
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: 1951; Downloads: 45
URL Full text (0,00 KB)

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Between-day reliability of a method for non-invasive estimation of muscle composition
Boštjan Šimunič, 2012, original scientific article

Found in: osebi
Keywords: Skeletal muscle, Tensiomyography, repeatability, validity
Published: 15.10.2013; Views: 1963; Downloads: 76
URL Full text (0,00 KB)

3.
Parents' opinions about their own and their children's lifestyle
Jera Gregorc, Mateja Videmšek, Jože Štihec, Boštjan Šimunič, 2011, original scientific article

Found in: osebi
Keywords: motor activity, athletic activity, active lifestyle, children, parents
Published: 15.10.2013; Views: 3277; Downloads: 54
URL Full text (0,00 KB)

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Longitudinalna analiza arhitekture golenske mišice štiri do šest letnih otrok
Boštjan Šimunič, Katja Koren, 2012, published scientific conference contribution

Found in: osebi
Keywords: skeletna mišica, gastrocnemius medialis, ultrazvok, kot penacije
Published: 15.10.2013; Views: 2426; Downloads: 24
URL Full text (0,00 KB)

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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: 1970; Downloads: 51
URL Full text (0,00 KB)

8.
Whole muscle contractile parameters and thickness loss during 35-day bed rest
Rado Pišot, Marco Narici, Boštjan Šimunič, Maarten D. de Boer, Olivier Seynnes, Mihaela Jurdana, Gianni Biolo, Igor B. Mekjavić, 2008, original scientific article

Abstract: Extended exposure to microgravity leads to significant musculoskeletal adaptations. Contractile parameters of four skeletal muscles (biceps brachii-BB, vastus medialis-VM, biceps femoris-BF and gastrocnemius medialis-GM) were measured in ten healthy males (aged 22.3 +/- 2.2 years) during 35 days of horizontal bed rest by a mechanomyography-based method termed 'tensiomyography' (TMG). Two contractile parameters: contraction time (Tc) and maximal displacement (Dm) were individually measured from electrically evoked maximal single twitch TMG response of all four muscles before and after bed rest. Significant changes in Tc were found after bed rest, as shown by an increase in GM muscle Tc by 18% (p < 0.01). Dm values significantly increased (p < 0.01) after bed rest, by 24, 26 and 30% in the VM, BF and GM muscles, respectively. In the GM, the change in Dm significantly correlated with the decrease in muscle thickness (r = -0.70, p < 0.01). In conclusion, bed rest induced changes in both Dm and Tc of the TMG signal; changes in Dm being inversely related to those of muscle thickness. Amongst the investigated muscles, most affected, in terms of atrophy and mechanical alterations, were those of the lower limbs. The observed increase in Dm may be attributed to a decrease in muscle, as well as tendon stiffness, causing larger muscle fibre and non-contractile tissue oscillations following contraction.
Found in: osebi
Keywords: Bed rest, skeletal muscle, muscle contraction, muscle thickness, mechanomyography, tensiomiography, ultrasound
Published: 15.10.2013; Views: 2115; Downloads: 60
URL Full text (0,00 KB)
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