Skeletal muscle fiber composition may modify the effect of nutrition on body composition in young females

Becoming a World Champion Powerlifter at 71 Years of Age: It Is Never Too Late to Start Exercising

This case study assessed body composition, muscle strength, cardiorespiratory fitness, and metabolic health of the present female world champion powerlifter in the 70+ age category who started resistance exercise training at 63 years of age with no prior experience with structured exercise training. Measures of body composition (magnetic resonance imaging, computed tomography, and dual-energy X-ray absorptiometry scanning, leg volume); strength (one-repetition maximum leg press and extension, maximum voluntary contraction, and handgrip strength); physical function (short physical performance battery); cardiorespiratory fitness (peak oxygen consumption); and metabolic health (oral glucose tolerance test) were assessed. In addition, a muscle biopsy was collected to assess muscle fiber type distribution and cross-sectional area (CSA). Where possible, data were compared with previously (un)published sex- and age-matched data using z scores. Skeletal muscle mass index was calculated by dividing limb muscle mass by height squared. Data from the control groups are expressed as mean ± 95% confidence interval. Our participant (age: 71 years; body mass: 64.5 kg; body mass index: 27.6 kg/m2) reported a good bone mineral density of 1.09 g/cm2 (T score between -1 and +1) and very low values of abdominal and organ body fat (i.e., between 20% and 70% lower compared with a reference group of postmenopausal women). In addition, she showed a 33% greater skeletal muscle mass index when compared with healthy, older female control subjects (7.9 vs. 5.9 [5.7-6.2] kg/m2; n = 61) as well as 37% greater muscle quadriceps CSA (63.8 vs. 46.6 [44.5-48.7] cm2; n = 48) and 46% greater Type II muscle fiber CSA (4,536 vs. 3,097 [2,707-3,488] μm2; n = 19). Absolute leg press muscle strength was 36% greater (190 vs. 140 [132-147] kg; n = 30) and handgrip strength was 33% greater (33 vs. 25 [23-26] kg; n = 48) when compared with healthy, age-matched controls. In conclusion, even for resistance exercise naïve individuals, starting exercise at an advanced age can lead to improvements in body composition and muscle strength allowing older adults to reduce the risk for developing metabolic syndrome, live independently, and even compete at a world class level.

The Role of Nutrition and Body Composition on Metabolism

Metabolism encompasses the entire array of chemical reactions continuously occurring within the body that sustain life and maintain normal physiological functions [...].

Evidence That Skeletal Muscles Modulate HDL-Cholesterol in Metabolic Healthy Young Adults

The aim of this study was to investigate whether skeletal muscle (SM) mass correlates with plasma lipids in metabolic healthy young adults. The study was designed as a retrospective observational monocentric study. Data on plasma lipids and SM mass of subjects attending our institution from 1999 to 2014 were analyzed. Inclusion criteria were being 18-45 years old and in apparently good health. SM mass was evaluated by bioelectrical impedance analysis (BIA) using the equation proposed by Janssen and normalized to height as skeletal muscle index (SMI: SM mass/height2). The association between SMI and plasma lipids levels was examined using a crude and adjusted linear regression model including age, sex, BMI and waist circumference as additional covariates. The study population consisted of 450 subjects (273 females) without metabolic syndrome (12.2% with normal body weight, 33.1% overweight, and 54.7% with obesity). SMI, total-cholesterol, LDL-cholesterol, and Triglycerides were higher, whereas HDL-cholesterol was lower in overweight and obese patients as compared with normal weight subjects. SMI was inversely associated with HDL-cholesterol in female patients with obesity but not in male patients with obesity, in normal- or over-weight subjects (p < 0.05). These results suggest that changes in SM mass occurring in obesity could have a role in worsening lipid profile with special reference to HDL-cholesterol.

Type IIx muscle fibers are related to poor body composition, glycemic and lipidemic blood profiles in young females: the protective role of type I and IIa muscle fibers

PURPOSE

The aim of the present study was to investigate the association between muscle fiber composition, body composition, resting glycemic-lipidemic blood profiles, in apparently healthy, young, active females.

METHODS

Thirty-four young healthy female volunteers were allocated into two groups, depending on their Vastus Lateralis type IIx muscle fibers percent cross-sectional area (%CSA; H: high type IIx %CSA; L: low type IIx %CSA). Body composition was determined via dual-energy X-ray absorptiometry. Venous blood samples were collected for the determination of resting serum glucose, Insulin, Apo-A1, HOMA-IR, triglycerides (TG), total cholesterol (TC), High-density lipoprotein (HDL-C), and Low-density lipoprotein (LDL-C) concentrations. Nutritional intake was also evaluated.

RESULTS

Individuals of the H group have significantly higher body mass, body fat percentage-mass, and resting blood indices of glycemic and lipidemic profiles, compared to those of L group (p < 0.001). Increased type IIx and low type I, IIa muscle fibers %CSAs were linked with poorer body composition, glycemic and lipidemic blood profiles (r: - 0.722 to 0.740, p < 0.001). Linear regression analyses revealed that the impact of muscle fibers %CSA (B coefficients ranged between - 0.700 and 0.835) on the above parameters, was at least, of the same or even of greater magnitude as that of body composition and daily nutritional intake (B: - 0.700 to 0.666).

CONCLUSION

Increased type IIx and low Type I, IIa %CSAs are associated with poorer body composition and glycemic-lipidemic profiles in young healthy females. The contribution of the muscle fiber %CSA on health status seems to be comparable to that of nutrition and body composition.

Muscle fiber phenotype: a culprit of abnormal metabolism and function in skeletal muscle of humans with obesity

The proportion of the different types of fibers in a given skeletal muscle contributes to its overall metabolic and functional characteristics. Greater proportion of type I muscle fibers is associated with favorable oxidative metabolism and function of the muscle. Humans with obesity have a lower proportion of type I muscle fibers. We discuss how lower proportion of type I fibers in skeletal muscle of humans with obesity may explain metabolic and functional abnormalities reported in these individuals. These include lower muscle glucose disposal rate, mitochondrial content, protein synthesis, and quality/contractile function, as well as increased risk for heart disease, lower levels of physical activity, and propensity for weight gain/resistance to weight loss. We delineate future research directions and the need to examine hybrid muscle fiber populations, which are indicative of a transitory state of fiber phenotype within skeletal muscle. We also describe methodologies for precisely characterizing muscle fibers and gene expression at the single muscle fiber level to enhance our understanding of the regulation of muscle fiber phenotype in obesity. By contextualizing research in the field of muscle fiber type in obesity, we lay a foundation for future advancements and pave the way for translation of this knowledge to address impaired metabolism and function in obesity.