1,270 research outputs found

    Comparison of MRI and DXA to measure muscle size and age-related atrophy in thigh muscles.

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    OBJECTIVES Magnetic resonance imaging (MRI) and dual-energy x-ray absorptiometry (DXA) were used to examine the thigh lean mass in young and old men and women. METHODS A whole-body DXA scan was used to estimate thigh lean mass in young (20 men; 22.4卤3.1y; 18 women; 22.1卤2.0y) and older adults (25 men; 72.3卤4.9y; 28 women; 72.0卤4.5y). Thigh lean mass determined with a thigh scan on the DXA or full thigh MRI scans were compared. RESULTS Although the thigh lean mass quantified by DXA and MRI in young and older participants were correlated (R(2)=0.88; p<0.001) the magnitude of the differences in thigh lean mass between young and old was smaller with DXA than MRI (old vs. young men 79.5卤13.1% and 73.4卤11.2%; old vs. young women 88.6卤11.8% and 79.4卤12.3%, respectively). Detailed analysis of MRI revealed 30% smaller quadriceps muscles in the older than young individuals, while the other thigh muscles were only 18% smaller. CONCLUSIONS DXA underestimates the age-related loss of thigh muscle mass in comparison to MRI. The quadriceps muscles were more susceptible to age-related atrophy compared with other thigh muscles

    The relationship between exercise-induced muscle fatigue, arterial blood flow and muscle perfusion after 56 days of muscle unloading

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    In the light of the dynamic nature of habitual plantar flexor activity, we utilized an incremental isokinetic exercise test (IIET) to assess the work-related power deficit (WoRPD) as a measure for exercise-induced muscle fatigue before and after prolonged calf muscle unloading and in relation to arterial blood flow and muscle perfusion. Eleven male subjects (31 卤 6 years) wore the HEPHAISTOS unloading orthosis unilaterally for 56 days. It allows habitual ambulation while greatly reducing plantar flexor activity and torque production. Endpoint measurements encompassed arterial blood flow, measured in the femoral artery using Doppler ultrasound, oxygenation of the soleus muscle assessed by near-infrared spectroscopy, lactate concentrations determined in capillary blood and muscle activity using soleus muscle surface electromyography. Furthermore, soleus muscle biopsies were taken to investigate morphological muscle changes. After the intervention, maximal isokinetic torque was reduced by 23路4 卤 8路2% (P<0路001) and soleus fibre size was reduced by 8路5 卤 13% (P = 0路016). However, WoRPD remained unaffected as indicated by an unchanged loss of relative plantar flexor power between pre- and postexperiments (P = 0路88). Blood flow, tissue oxygenation, lactate concentrations and EMG median frequency kinematics during the exercise test were comparable before and after the intervention, whereas the increase of RMS in response to IIET was less following the intervention (P = 0路03). In conclusion, following submaximal isokinetic muscle work exercise-induced muscle fatigue is unaffected after prolonged local muscle unloading. The observation that arterial blood flow was maintained may underlie the unchanged fatigability

    Impact of vaping and smoking on maximum respiratory pressures and respiratory function

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    The effects of electronic-cigarette use (vaping), marketed as a healthier alternative to cigarette smoking (CS), on lung function remain equivocal. Therefore, this study assessed and compared the effects of vaping and CS on maximum respiratory pressures (MRP), respiratory function and carboxyhaemoglobin levels. Forty-four young healthy participants were recruited: vapers (n聽=聽12), cigarette smokers (n聽=聽14), and people who had never vaped nor smoked (control) group (n聽=聽18). Spirometry, MRP and carboxyhaemoglobin levels were measured. Both smokers and vapers had a lower Forced expiratory volume in the first second (FEV1), Peak expiratory flow, FEV1/Forced vital capacity (FEV1/FVC), Forced expiratory flow at 25%, 25鈥75% of FVC, FEF25-75pred% and higher carboxyhaemoglobin% than controls (p聽<聽0.05). In smokers, but not in vapers, FEV1pred% was lower than in controls (p聽<聽0.01). MRP did not differ significantly between the three groups. Vaping has similar detrimental effects as CS on pulmonary function and may thus not be a healthier alternative to smoking

    Age-related skeletal muscle dysfunction is aggravated by obesity: An investigation of contractile function, implications and treatment

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    Obesity is a global epidemic and coupled with the unprecedented growth of the world鈥檚 older adult population, a growing number of individuals are both old and obese. Whilst both ageing and obesity are associated with an increased prevalence of chronic health conditions and a substantial economic burden, evidence suggests that the coincident effects exacerbate negative health out-comes. A significant contributor to such detrimental effects may be the reduction in the contractile performance of skeletal muscle, given that poor muscle function is related to chronic disease, poor quality of life and all-cause mortality. Whilst the effects of ageing and obesity independently on skeletal muscle function have been investigated, the combined effects are yet to be thoroughly explored. Given the importance of skeletal muscle to whole-body health and physical function, the present study sought to provide a review of the literature to: (1) summarise the effect of obesity on the age-induced reduction in skeletal muscle contractile function; (2) understand whether obesity effects on skeletal muscle are similar in young and old muscle; (3) consider the consequences of these changes to whole-body functional performance; (4) outline important future work along with the potential for targeted intervention strategies to mitigate potential detrimental effects

    Hysteresis in muscle

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    This paper presents examples of hysteresis from a broad range of scientific disciplines and demonstrates a variety of forms including clockwise, counterclockwise, butterfly, pinched and kiss-and-go, respectively. These examples include mechanical systems made up of springs and dampers which have been the main components of muscle models for nearly one hundred years. For the first time, as far as the authors are aware, hysteresis is demonstrated in single fibre muscle when subjected to both lengthening and shortening periodic contractions. The hysteresis observed in the experiments is of two forms. Without any relaxation at the end of lengthening or shortening, the hysteresis loop is a convex clockwise loop, whereas a concave clockwise hysteresis loop (labeled as "kiss-and-go") is formed when the muscle is relaxed at the end of lengthening and shortening. This paper also presents a mathematical model which reproduces the hysteresis curves in the same form as the experimental data

    Reactive Jumps Preserve Skeletal Muscle Structure, Phenotype, and Myofiber Oxidative Capacity in Bed Rest

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    漏 Copyright 漏 2020 Blottner, Hastermann, Weber, Lenz, Gambara, Limper, Rittweger, Bosutti, Degens and Salanova. Identification of countermeasures able to prevent disuse-induced muscle wasting is crucial to increase performance of crew members during space flight as well as ameliorate patient鈥檚 clinical outcome after long immobilization periods. We report on the outcome of short but high-impact reactive jumps (JUMP) as countermeasure during 60 days of 6掳 head-down tilt (HDT) bed rest on myofiber size, type composition, capillarization, and oxidative capacity in tissue biopsies (pre/post/recovery) from the knee extensor vastus lateralis (VL) and deep calf soleus (SOL) muscle of 22 healthy male participants (Reactive jumps in a sledge, RSL-study 2015鈥2016, DLR:envihab, Cologne). Bed rest induced a slow-to-fast myofiber shift (type I 鈥>II) with an increased prevalence of hybrid fibers in SOL after bed rest without jumps (control, CTRL, p = 0.016). In SOL, JUMP countermeasure in bed rest prevented both fast and slow myofiber cross-sectional area (CSA) decrements (p = 0.005) in CTRL group. In VL, bed rest only induced capillary rarefaction, as reflected by the decrease in local capillary-to-fiber ratio (LCFR) for both type II (pre vs. post/R + 10, p = 0.028/0.028) and type I myofibers (pre vs. R + 10, p = 0.012), which was not seen in the JUMP group. VO2maxFiber (pL 脳 mm鈥1 脳 min鈥1) calculated from succinate dehydrogenase (SDH)-stained cryosections (OD660 nm) showed no significant differences between groups. High-impact jump training in bed rest did not prevent disuse-induced myofiber atrophy in VL, mitigated phenotype transition (type I 鈥 >II) in SOL, and attenuated capillary rarefaction in the prime knee extensor VL however with little impact on oxidative capacity changes

    The impact of a high-fat diet in mice is dependent on duration and age, and differs between muscles.

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    Prolonged high-fat diets (HFD) can cause intramyocellular lipids (IMCL) accumulation that may negatively affect muscle function. We investigated the duration of a HFD required to instigate these changes, and whether effects are muscle-specific and aggravated in older age. Muscle morphology was determined in the soleus, extensor digitorum longus (EDL) and diaphragm muscles from female CD-1 mice divided into 5 groups: young fed a HFD for 8 weeks (YS-HFD, n=16), young fed a HFD for 16 weeks (YL-HFD, n=28) and young control (Y-CON, n=28). The young animals were 20 weeks old at the end of the experiment. Sixty 70-week-old female CD-1 mice received either a normal diet (O-CON, n=30) or a HFD for 9 weeks (OS-HFD, n=30). Body mass, body mass index and IMCL content increased in old OS-HFD (p鈮0.003). In the young mice, this increase was seen in YL-HFD and not YS-HFD (p鈮0.006). The soleus and diaphragm fibre cross-sectional area (FCSA) in YL-HFD was larger compared to Y-CON (p鈮0.004) while old mice had a larger soleus FCSA compared to CON after only 9 weeks on a HFD (p<0.001). The FCSA of the EDL muscle did not differ significantly between groups. Oxidative capacity of fibres increased in young only, irrespective of HFD duration (p<0.001). High-fat diet-induced morphological changes occur earlier in the old animals when compared to young, and adaptations to HFD are muscle-specific with the EDL being least responsive

    Skeletal muscle properties and fatigue resistance in relation to smoking history

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    Although smoking-related diseases, such as chronic obstructive pulmonary disease (COPD), are often accompanied by increased peripheral muscle fatigability, the extent to which this is a feature of the disease or a direct effect of smoking per se is not known. Skeletal muscle function was investigated in terms of maximal voluntary isometric torque, activation, contractile properties and fatigability, using electrically evoked contractions of the quadriceps muscle of 40 smokers [19 men and 21 women; mean (SD) cigarette pack years: 9.9 (10.7)] and age- and physical activity level matched non-smokers (22 men and 23 women). Maximal strength and isometric contractile speed did not differ significantly between smokers and non-smokers. Muscle fatigue (measured as torque decline during a series of repetitive contractions) was greater in smokers (P聽=聽0.014), but did not correlate with cigarette pack years (r聽=聽0.094, P聽=聽0.615), cigarettes smoked per day (r聽=聽10.092, P聽=聽0.628), respiratory function (%FEV1pred) (r聽=聽鈭0.187, P聽=聽0.416), or physical activity level (r聽=聽鈭0.029, P聽=聽0.877). While muscle mass and contractile properties are similar in smokers and non-smokers, smokers do suffer from greater peripheral muscle fatigue. The observation that the cigarette smoking history did not correlate with fatigability suggests that the effect is either acute and/or reaches a ceiling, rather than being cumulative. An acute and reversible effect of smoking could be caused by carbon monoxide and/or other substances in smoke hampering oxygen delivery and mitochondrial function
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