Muscle research: A tour d'horizon

The Special Issue on the "Muscular Structure, Physiology and Metabolism" was proposed in order to maintain the referenced scientific community abreast with recent research advancements regarding the morphology, functionality, and metabolism of muscle tissue, including a total of eighteen published papers, of which twelve were original research manuscripts and six were review papers [...]

Are body circumferences able to predict strength, muscle mass and bone characteristics in obesity? A preliminary study in women

Measurement of body circumferences (BCs) is widely used as an anthropometric tool to assess body composition and health risk in obese individuals. In this preliminary work we evaluated the association of several BCs with Dual-energy X-ray Absorptiometry (DXA)-measured lean mass as well as leg press test scores with an aim at exploring the potential of BCs as predictor of body composition and muscle strength. A total of 34 female participants aged 47.3\ub17.6 y who were obese (BMI, 30.4-43.7 kg/m2) were recruited. The upper arm (relaxed), wrist, chest, waist, hip, thigh, and calf circumferences were measured. The skinfold-corrected muscle (including bone) circumferences at the arm, thigh, and calf site were also calculated. Lean mass components were measured by DXA with a Hologic QDR Explorer scanner according to the manufacturer's procedures. Lower limbs strength was assessed with the 1-Repetition Maximum leg press. Bivariate association between variables was assessed with the Spearman's correlation coefficient after the Benjamini and Hochberg False Discovery Rate procedure. Predictive equations were developed using stepwise multiple regression analysis. Several statistically significant correlations (Benjamini and Hochberg corrected P [Pc] < 0.05) were present between BCs and DXA-measured body composition variables, and leg press test scores with special regard to the chest, arm, waist, and hip circumferences. Multiple regression analysis yielded statistically significant predictive models (Pc < 0.05 for all; adjusted R2 ranging 0.123 - 0.504; standard error of the estimate ranging 4.0% - 11% of the mean measured value) for all body composition as well as leg press outcomes. The current findings show that BCs represent a simple, suitable anthropometric measurement with a potential to predict several lean mass components as well as lower limbs strength in obese females. The proposed predictors need to be validated in a larger sample of participants and in obese males

EFFECT OF A COMPETITIVE SEASON ON ANTHROPOMETRY AND THREE-COMPARTMENT BODY COMPOSITION IN FEMALE HANDBALL PLAYERS

The objective of this work was to investigate the anthropometry and 3-compartment body composition characteristics of female team handball players preseason and postseason. Forty-three Caucasian female handball players were recruited for this study. Linear anthropometry, skinfold measurement, and dual-energy X-ray absorptiometry (DXA) were used to investigate body dimensions and composition (fat mass, lean mass, mineral mass) over an 8-month competitive season. A complete dataset (pre- and postseason) was available for 33 handball players. Repeated measure ANOVA showed no change in body mass, BMI, sum of eight skinfolds, and most body circumferences over the season. At the total body level, bone mineral content (BMC) significantly increased postseason ( 1.64% P<0.0001), lean mass was unchanged, and fat mass and %fat mass were slightly decreased (-2.24% P=0.295; -0.4% P=0.229, respectively). DXA regional analysis showed that mineral mass was exclusively accrued in the upper and lower limbs postseason (upper 4.95% lower 1.7% P<0.0001 for both); lean mass increased in upper ( 5.3% P<0.0001) but not lower limbs, and fat mass did not change in either. When handball players were subdivided according to competitive level (elite/sub-elite) or playing position (goalkeeper, back, pivot, wing), no significant between-group difference was found postseason in circumferences, skinfolds, and body composition parameters. In conclusion, anthropometry of female handball players does not change significantly over the competitive season except for some fat redistribution; however, BMC increases in the limbs, and lean mass in upper limbs postseason. These findings are independent of competitive level (elite/sub-elite) and playing position. These results could serve as an important tool in the development of guidelines optimizing in-season training programmes for team handball

Different amount of training affects body composition and performance in High-Intensity Functional Training participants

The effects of High-Intensity Functional Training (HIFT) on body composition and the relationship of the latter with performance are not well defined. In this work we investigated, by means of Dual-energy X-ray Absorptiometry, the relative proportions of fat-, lean soft tissue-, and mineral mass in CrossFit\uae (CF, a popular mode of HIFT) participants (n = 24; age, 28.2 \ub1 3.39 y; BMI, 25.3 \ub1 2.04 kg/m2) with at least 1 year of CF training experience and weekly amount of training &gt; 10 h/w (n = 13; Higher Training, HT) or &lt; 10 h/w (n = 11; Lower Training, LT) as well as age- matched and BMI-matched physically active controls (CHT, CLT). Performance was assessed in the "Fran" workout. Data were analyzed by one-way or repeated measures ANOVA where needed. Association between variables was assessed with the Pearson's correlation coefficient r. Partial correlation was used where needed. Results showed that HT performed better than LT in the "Fran" (P &lt; 0.001) and they had higher whole-body bone mineral density (P = 0.026) and higher lean soft mass (P = 0.002), and borderline lower percent fat mass (P = 0.050). The main difference between CF participants (HT, LT) and their respective controls (CHT, CLT) was a lower adiposity in the former. In CF participants, performance positively correlated with appendicular lean soft tissue mass (P = 0.030). It can be concluded that, in CF participants, a higher amount of weekly training improves most notably lean body mass and increases performance in association with increased skeletal muscle mass. CF participation is especially effective in reducing fat mass vs. age- and BMI-matched physically active controls

Mild chronic whole body vibration does not affect bone mineral mass or density in young females

Whole body vibration (WBV) is increasingly being used in several physical therapy settings. In order to evaluate the ability of WBV to affect bone mineral component, thirty-six young (mean age 25.3 ± 5.26 yrs) healthy females underwent eight weeks of WBV exercise (nineteen minutes per session, two session a week; vibration amplitude 2.0-5.0 mm, vibration frequency 40-60 Hz). Bone mineral content (BMC) and density (BMD) were evaluated before and after the WBV trial using dual-energy X-ray absorptiometry in the whole body mode. Data were analyzed with repeated measures analysis of variance. Results show that neither BMC nor BMD were significantly affected by the WBV trial at the total body or regional skeletal level. It is concluded that, under the current experimental conditions, WBV exercise is not able to improve bone mineral parameters in young healthy females before the peak bone mass. Further investigation is required to recommend WBV for increasing bone quality parameters in premenopausal women

The role of age, sex, anthropometry, and body composition as determinants of physical fitness in nonobese children aged 6\u201312

PURPOSE: The determinants of physical fitness in children have been given limited attention. In particular, the relative role of chronological age, sex, anthropometry, and body composition in physical fitness of children has been barely investigated. This cross-sectional study investigated determinants of physical fitness using a set of predictive variables including, in addition to chronological age and sex, a large panel of anthropometric measurements as well as body composition. The study was carried out in a convenience sample of children aged 6\u201312 participating in a summer camp. METHODS: One-hundred-ninety-three children (128 males) fulfilled all requirements and entered analysis. Health-related physical fitness components (speed, muscular power and balance) were explored by means of field tests, namely the 30-m dash test for running speed, the standing long jump and the seated chest pass test for lower limbs and upper body muscular power, respectively, and the flamingo balance test for static balance. Determinants of physical fitness were investigated by regression analysis using chronological age, sex, anthropometry, and body composition in a hierarchical approach. To minimize the expected effect of collinearity in predictor variables, an original statistical approach using Random Forests analysis was adopted. RESULTS: Age predicted 45.2%, 43.6%, 35.6% and 25.6%; and sex 9.5%, 10.7%, 6.3% and 2.0% of variance in the 30-m dash, seated chest pass, standing long jump, and flamingo balance test, respectively. Anthropometry and body composition explained a limited or no percentage of variance. The adjusted R2 (root mean square error) was 0.61 (0.31 s), 0.45 (0.32 m), 0.58 (0.15 m) and 0.41 (0.75 logs) for the 30-m dash, seated chest pass, standing long jump, and flamingo balance test, respectively making these models useful when physical fitness tests are not feasible. CONCLUSIONS: We highlighted the respective role of chronological age, sex, anthropometry, and body composition in physical fitness of children in the wide age range 6\u201312 years. Data confirm and expand on previous literature by showing with a strictly conservative statistical approach that chronological age is a main determinant of physical fitness of both boys and girls, sex playing a limited role. The role of anthropometry was even less important, and no role was found for body composition. These findings should be considered when planning/implementing motor development or physical education programs

Satellite cells in skeletal muscle of the hibernating dormouse, a natural model of quiescence and re-activation: focus on the cell nucleus

Satellite cells (SCs) participate in skeletal muscle plasticity/regeneration. Activation of SCs implies that nuclear changes underpin a new functional status. In hibernating mammals, periods of reduced metabolic activity alternate with arousals and resumption of bodily functions, thereby leading to repeated cell deactivation and reactivation. In hibernation, muscle fibers are preserved despite long periods of immobilization. The structural and functional characteristics of SC nuclei during hibernation have not been investigated yet. Using ultrastructural and immunocytochemical analysis, we found that the SCs of the hibernating edible dormouse, Glis glis, did not show apoptosis or necrosis. Moreover, their nuclei were typical of quiescent cells, showing similar amounts and distributions of heterochromatin, pre-mRNA transcription and processing factors, as well as paired box protein 7 (Pax7) and the myogenic differentiation transcription factor D (MyoD), as in euthermia. However, the finding of accumulated perichromatin granules (i.e., sites of storage/transport of spliced pre-mRNA) in SC nuclei of hibernating dormice suggested slowing down of the nucleus-to-cytoplasm transport. We conclude that during hibernation, SC nuclei maintain similar transcription and splicing activity as in euthermia, indicating an unmodified status during immobilization and hypometabolism. Skeletal muscle preservation during hibernation is presumably not due to SC activation, but rather to the maintenance of some functional activity in myofibers that is able to counteract muscle wasting

Ultrastructural immunocytochemistry shows impairment of RNA pathways in skeletal muscle nuclei of old mice: A link to sarcopenia?

During aging, skeletal muscle is affected by sarcopenia, a progressive decline in muscle mass, strength and endurance that leads to loss of function and disability. Cell nucleus dysfunction is a possible factor contributing to sarcopenia because aging-associated alterations in mRNA and rRNA transcription/maturation machinery have been shown in several cell types including muscle cells. In this study, the distribution and density of key molecular factors involved in RNA pathways namely, nuclear actin (a motor protein and regulator of RNA transcription), 5-methyl cytosine (an epigenetic regulator of gene transcription), and ribonuclease A (an RNA degrading enzyme) were compared in different nuclear compartments of late adult and old mice myonuclei by means of ultrastructural immunocytochemistry. In all nuclear compartments, an age-related decrease of nuclear actin suggested altered chromatin structuring and impaired nucleus-to-cytoplasm transport of both mRNA and&nbsp;ribosomal subunits, while a decrease of 5-methyl cytosine and ribonuclease A in the nucleoli of old mice indicated an age-dependent loss of rRNA genes. These findings provide novel experimental evidence that, in the&nbsp;aging skeletal muscle, nuclear RNA pathways undergo impairment, likely hindering protein synthesis and contributing&nbsp;to the onset and progression of sarcopenia

The cell nuclei of skeletal muscle cells are transcriptionally active in hibernating edible dormice

<p>Abstract</p> <p>Background</p> <p>Skeletal muscle is able to react in a rapid, dynamic way to metabolic and mechanical stimuli. In particular, exposure to either prolonged starvation or disuse results in muscle atrophy. At variance, in hibernating animals muscle atrophy may be scarce or absent after bouts of hibernation i.e., periods of prolonged (months) inactivity and food deprivation, and muscle function is fully preserved at arousal. In this study, myocytes from the quadriceps muscle of euthermic and hibernating edible dormice were investigated by a combination of morphological, morphometrical and immunocytochemical analyses at the light and electron microscopy level. The focus was on cell nuclei and mitochondria, which are highly sensitive markers of changing metabolic rate.</p> <p>Results</p> <p>Findings presented herein demonstrate that: 1) the general histology of the muscle, inclusive of muscle fibre shape and size, and the ratio of fast and slow fibre types are not affected by hibernation; 2) the fine structure of cytoplasmic and nuclear constituents is similar in euthermia and hibernation but for lipid droplets, which accumulate during lethargy; 3) during hibernation, mitochondria are larger in size with longer cristae, and 4) myonuclei maintain the same amount and distribution of transcripts and transcription factors as in euthermia.</p> <p>Conclusion</p> <p>In this study we demonstrate that skeletal muscle cells of the hibernating edible dormouse maintain their structural and functional integrity in full, even after months in the nest. A twofold explanation for that is envisaged: 1) the maintenance, during hibernation, of low-rate nuclear and mitochondrial activity counterbalancing myofibre wasting, 2) the intensive muscle stimulation (shivering) during periodic arousals in the nest, which would mimic physical exercise. These two factors would prevent muscle atrophy usually occurring in mammals after prolonged starvation and/or inactivity as a consequence of prevailing catabolism. Understanding the mechanisms responsible for skeletal muscle preservation in hibernators could pave the way to prevention and treatment of muscle wasting associated with pathological conditions or ageing as well as life in extreme environments, such as ocean deeps or spaceflights.</p

Anthropometric prediction of DXA-measured percentage of fat mass in athletes with unilateral lower limb amputation

To date there is no anthropometric equation specific to athletes with unilateral lower limb amputation to estimate the percentage of fat mass (%FM). This study investigated the accuracy of a set of anthropometric equations validated on able-bodied populations to predict the %FM assessed by-means of dual-energy x-ray absorptiometry (DXA) in athletes with unilateral lower limb amputation. Furthermore, a predictive anthropometric equation specific to athletes with unilateral lower limb amputation was developed from skinfold thickness measurements using DXA as the reference method for the estimation of the %FM. Twenty-nine white male athletes with unilateral lower limb amputation underwent a DXA scan and an anthropometric assessment on the same day. The %FM, calculated through several existing anthropometric equations validated upon able-bodied populations, was compared with the DXA-measured %FM (%FM_DXA). Accuracy and agreement between the two methods was computed with two-tailed paired-sample t-test, concordance correlation coefficient, reduced major axis regression and Bland-Altman analysis. A stepwise multiple regression analysis with the %FM_DXA as the dependent variable and age and nine skinfold thicknesses as potential predictors was carried out and validated using a repeated 10-fold cross-validation. A linear regression analysis with the sum of nine skinfolds as the independent variable was also carried out and validated using a repeated 10-fold cross-validation. The results showed that the anthropometric equations validated on able-bodied populations are inaccurate in the estimation of %FM_DXA with an average bias ranging from 0.51 to -13.70%. Proportional bias was also found revealing that most of the anthropometric equations considered, tended to underestimate/overestimate the %FM_DXA as body fat increased. Regression analysis produced two statistically significant models (P &lt; 0.001 for both) which were able to predict more than 93% of total variance of %FM_DXA from the values of four skinfold measurements (i.e., thigh, abdominal, subscapular and axillary skinfold measurements) or from the sum of 9 skinfolds. Repeated cross-validation analysis highlighted a good predictive performance of the proposed equations. The predictive equations proposed in this study represent a useful tool for clinicians, nutritionists, and physical conditioners to evaluate the physical and nutritional status of athletes with unilateral lower limb amputation directly in the field