One-repetition maximum strength test represents a valid means to assess leg strength in vivo in humans.

Skeletal muscle strength is often determined to evaluate the adaptive response to an exercise intervention programme. Although dynamometry is considered the "gold standard" for the assessment of muscle strength in vivo, one-repetition maximum (1-RM) testing performed on training-specific equipment is more commonly applied. We assessed the validity of specific knee extension 1-RM testing by comparison with dynamometry in a heterogeneous population (n = 55). All participants performed 1-RM tests on regular leg extension and leg press machines. Additionally, isometric (at seven different knee angles) and isokinetic (at four different velocities) knee extension peak torques were determined. Pearson's r was calculated for the relationship between 1-RM data and peak torques for the entire population and for subgroups defined by age and gender. One-repetition maximum strength correlated strongly with the dynamometer results. One-repetition maximum leg extension correlated more strongly with peak torques than did 1-RM leg press (0.78 </= r </= 0.88 vs. 0.72 </= r </= 0.77; P < 0.001). Similar correlations were observed in all subgroups. We conclude that 1-RM testing represents a valid means to assess leg muscle strength in vivo in young and elderly men and women. Considering the importance of training specificity in strength assessment, we argue that 1-RM testing can be applied to assess changes in leg muscle strength following an exercise intervention

Satellite cell content is specifically reduced in type II skeletal muscle fibers in the elderly

Satellite cells (SC) are essential for skeletal muscle growth and repair. As sarcopenia is associated with type II muscle fiber atrophy, we hypothesized that SC content is specifically reduced in the type II fibers in the elderly. A total of 8 elderly (E:76+/-1y) and 8 young (Y:20+/-1y) healthy males were selected. Muscle biopsies were collected from the vastus lateralis in both legs. ATPase staining and a pax7-antibody were used to determine fiber type specific SC content (i.e. pax7-positive SC) on serial muscle cross-sections. In contrast to the type I fibers, the proportion and mean cross-sectional area of the type II fibers were substantially reduced in the E versus the Y. The number of SC per type I fiber was similar in E and Y. However, the number of SC per type II fiber was substantially lower in the E versus the Y (0.044+/-0.003 vs 0.080+/-0.007; P<0.01). In addition, in the type II fibers the number of SC relative to the total number of nuclei and the number of SC per fiber area were also significantly lower in the E. This study is the first to show type II fiber atrophy in the elderly to be associated with a fiber type specific decline in SC content. The latter is evident when SC content is expressed per fiber or per fiber area. The decline in SC content might be an important factor in the etiology of type II muscle fiber atrophy, which accompanies the loss of skeletal muscle with aging. Key words: skeletal muscle, sarcopenia, muscle stem cells, atrophy, metabolism

Characteristics of muscle fiber type are predictive of skeletal muscle mass and strength in elderly men

OBJECTIVES: To investigate the relationship between skeletal muscle fiber type-specific characteristics, circulating hormone concentrations, and skeletal muscle mass and strength in older men. DESIGN: Cross-sectional analyses. SETTING: University research center. PARTICIPANTS: Forty-one community dwelling elderly men (>/= 65). MEASUREMENTS: Leg strength (1-repetition maximum, 1RM) and whole-body and limb muscle mass were determined, and muscle fiber type composition, cross-sectional area (CSA), myonuclear content, and satellite cell (SC) content were assessed in skeletal muscle biopsy samples. In addition, blood samples were collected to determine serum testosterone, sex hormone-binding globulin, insulinlike growth factor (IGF)-1, and IGF binding protein-3 concentrations. RESULTS: Muscle mass correlated with muscle strength (0.41 </= correlation coefficient (r) </= 0.72; P < .01). Muscle fiber CSA, myonuclear content, and SC content were significantly lower in type II than in type I muscle fibers. Myonuclear and SC content were positively correlated with muscle fiber CSA. Furthermore, greater muscle fiber CSA (type I and II) was associated with greater thigh muscle area and muscle strength (0.30 </= r </= 0.45; P < .05). Testosterone concentration was positively correlated with muscle mass and muscle fiber CSA. Regression analysis showed that SC content, myonuclear content, and testosterone concentration are predictive of muscle fiber CSA. Furthermore, muscle mass and type II muscle fiber CSA are predictive of muscle strength. CONCLUSION: Skeletal muscle mass and strength in elderly men are positively correlated with muscle fiber type-specific CSA, myonuclear content, and SC content. These findings support the assumption that a decline in SC content plays an important role in age-related decline in muscle mass and strength

Електродинамічні характеристики розподілено-зв'язаних діелектричних хвилеводів з екраном змінної провідності

Широке розповсюдження та використання, як окремих приладів так і елементної бази електроніки НВЧ, отримали хвилеводні системи із розподіленим зв‘язком. Найбільш відомими серед них є спрямовані відгалужувачі, хвилеводно-пучкові перетворювачі, елементи сумарнорізнецевих перетворювачів сигналів, пристрої на базі планарних лінз Люненберга. Тому питання оптимізації вже відомих та пошук нових способів керування міжхвилеводним розподіленим зв‘язком в таких системах є актуальними

Nutritional supplementation to enhance the efficacy of exercise training in older adults: what is the evidence from the latest randomized controlled trials?

Purpose of review This review summarizes recent studies that assessed whether nutritional supplementation enhances the efficacy of exercise training in older adults, focusing on the benefits for physical/functional performance of protein, vitamin D, or multi-ingredient supplementation. Recent findings Studies applying long-term exercise training strongly support the benefits of different exercise regimens for muscle strength and function but most studies do not provide direct evidence for protein, vitamin D, or multi-ingredient supplementation to further augment such improvements in older adults. Several methodological limitations are addressed that likely limited the reliability to convincingly establish or refute any additive effects of supplementation. Only when specifically tailored to the population under study, ensuring proper intensity, duration, and adherence to exercise, and aiming for a daily intake of similar to 1.5 g protein per kg body mass, and similar to 800 IU of vitamin D supplementation, there appears to be some potential to augment the efficacy of long-term exercise training in older adults, with potentially greater benefits in compromised older subpopulations. There is some support for the efficacy of nutritional supplementation to further augment the beneficial effects of prolonged exercise training in older adults but any intervention needs tailoring of both the exercise and the nutritional intervention towards the intended (sub)population

The impact of sarcopenia and exercise training on skeletal muscle satellite cells.

It has been well established that the age-related loss of muscle mass and strength, or sarcopenia, impairs skeletal muscle function and reduces functional performance at a more advanced age. Skeletal muscle satellite cells (SC), as precursors of new myonuclei, have been suggested to be involved in the development of sarcopenia. In accordance with the type II muscle fiber atrophy observed in the elderly, recent studies report a concomitant fiber type specific reduction in SC content. Resistance type exercise interventions have proven effective to augment skeletal muscle mass and improve muscle function in the elderly. In accordance, recent work shows that resistance type exercise training can augment type II muscle fiber size and reverse the age-related decline in SC content. The latter is supported by an increase in SC activation and proliferation factors that generally appear following exercise training. Present findings strongly suggest that the skeletal muscle SC control myogenesis and have an important, but yet unresolved, function in the loss of muscle mass with aging. This review discusses the contribution of skeletal muscle SC in the age-related loss of muscle mass and the efficacy of exercise training as a means to attenuate and/or reverse this process

The robustness of age-related gait adaptations: Can running counterbalance the consequences of ageing?

Previous studies showed age-related redistribution of joint torques from ankle joint plantar flexion to hip joint extension in gait. In the present study it was hypothesized that running can prevent the occurrence of this joint torque redistribution. Four groups of subjects participated in this study (young and elderly both physically active and inactive). All subjects walked at a comfortable, preferred velocity and at an imposed velocity of 1.5m/s. Kinematics of lower limb segments and ground reaction forces were assessed. Inverse dynamics method was applied to determine torques around ankle, knee and hip joints. A redistribution of joint torques from plantar flexion to hip joint extension was found to occur in both active and inactive elderly. However, the active elderly had a larger increase of the hip extension torque. By this they are able to maintain the support torque at the level of young subjects. Inactive elderly displayed reduced support torques. It is concluded that the age-related redistribution of joint torques is an important phenomenon. Frequent running does not prevent this shift. Active elderly increase this redistribution to compensate for muscle function reduction. AD - Department of Human Movement Science, Nutrition and Toxicology Research Institute Maastricht (NUTRIM), Faculty of Health Sciences, Universiteit Maastricht, The Netherlands

Continuous endurance-type exercise training does not modulate satellite cell content in obese type 2 diabetes patients.

Endurance-type exercise training represents a cornerstone in type 2 diabetes treatment. However, the effects of prolonged continuous, endurance-type exercise on muscle fiber characteristics remain equivocal. Fifteen obese male type 2 diabetes patients ( 61 ± 6 years ) participated in a 6-month continuous, endurance-type exercise program. Muscle biopsies were collected before, and after 2 and 6 months of intervention. Muscle fiber type–specific composition, size, and satellite cell ( SC ) and myonuclear content were determined by immunohistochemistry. Although continuous endurance-type exercise training lowered total body weight and reduced fat mass, no changes were observed in leg lean mass. At baseline, SC content was significantly lower in type II compared with type I muscle fibers. No change in SC content was observed after exercise training. Continuous endurance-type exercise training lowers fat mass, but it does not increase leg lean mass and/or modulate muscle fiber characteristics in type 2 diabetes patients