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Lower physical activity is associated with skeletal muscle fat content in girls.

ABSTRACT: Fat contained within skeletal muscle is strongly associated with obesity, type 2 diabetes mellitus, and metabolic syndrome. Physical inactivity may be a risk factor for greater fat infiltration within skeletal muscle during growth.We sought to examine the relationship between physical activity and skeletal muscle fat content of the calf and thigh in girls.Data from 464 girls, age 8-13 yr, were used to examine the relationship between physical activity and skeletal muscle fat content of the calf and thigh. Calf and thigh muscle density (mg·cm(-3)), an index of skeletal muscle fat content, was assessed at the 66% tibia and 20% femur sites relative to the respective distal growth plates of the nondominant limb using peripheral quantitative computed tomography. Physical activity level was classified by past-year physical activity questionnaire score.Muscle densities of the calf and thigh were inversely correlated with percent total body fat (r = -0.37 and -0.48, P values < 0.001) and total body fat mass (r = -0.33 and -0.40, P values < 0.001). Multiple linear regression with physical activity, ethnicity, maturity offset, and muscle cross-sectional area as independent variables showed that physical activity was independently associated with muscle densities of the calf (? = 0.14, P = 0.002) and thigh (? = 0.15, P < 0.001). Thus, lower physical activity was associated with higher skeletal muscle fat content.Our results suggest that a lower level of physical activity may lead to excess skeletal muscle fat content of the calf and thigh in girls.

SUBMITTER: Farr JN

PROVIDER: S-EPMC3819115 | biostudies-literature | 2012 Jul

REPOSITORIES: biostudies-literature

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Lower physical activity is associated with skeletal muscle fat content in girls.

Farr Joshua Nicholas JN Van Loan Marta D MD Lohman Timothy G TG Going Scott B SB

Medicine and science in sports and exercise 20120701 7

<h4>Unlabelled</h4>Fat contained within skeletal muscle is strongly associated with obesity, type 2 diabetes mellitus, and metabolic syndrome. Physical inactivity may be a risk factor for greater fat infiltration within skeletal muscle during growth.<h4>Purpose</h4>We sought to examine the relationship between physical activity and skeletal muscle fat content of the calf and thigh in girls.<h4>Methods</h4>Data from 464 girls, age 8-13 yr, were used to examine the relationship between physical ac ...[more]

PMID: 22217562

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Project description:Introduction/Purpose: Physical activity and sedentary time may associate with physical fitness and body composition. Yet, there exists some observational studies that have investigated the associations of device-based measures of sedentary time and physical activity (PA) with cardiorespiratory fitness (CRF) and body composition but associations with muscular fitness (MF) are less studied. Methods: Objective sedentary time and physical activity was measured by a hip worn accelerometer from 415 young adult men (age: mean 26, standard deviation 7 years). Cardiorespiratory fitness (VO2max) (CRF) was determined using a graded cycle ergometer test until exhaustion. Maximal force of lower extremities was measured isometrically and lower body power was assessed using standing long jump (MF). Body composition was determined with bioimpedance method. Single and compositional approach was used in regression analysis. Results: Mean sedentary time was 707 (standard deviation 133) minutes per day (77 ± 8% of the wear time). Volumes of all PA intensities were positively associated with CRF and associations showed linearly increasing magnitudes with higher intensities in single regression models adjusted for age and smoking (p < 0.001). Similarly, PA intensities were positively associated with lower body MF, however, with weaker associations (p < 0.005). After further adjustment for resistance training, the associations remained significant. The associations of the relative distribution of time within sedentary behavior (SB), light intensity PA (LPA) and moderate-to-vigorous PA (MVPA) behaviors as a whole with using compositional analysis further revealed that within the composition MVPA and SB were positively associated with CRF and MF (p < 0.001), while LPA was not. In addition, within the composition, accumulated PA bouts lasting more than 3 min were consistently associated with CRF and MF, and with all body composition variables (p < 0.001), while sedentary time was associated with body fat percentage (p < 0.001). Conclusion: Promoting physical activity and reducing sedentary time may have positive influence on physical fitness and body fat content, and thereby may offer positive health effects. Physical activity of higher intensities may offer greater benefits.

Project description:BackgroundThe exact impact of ageing on skeletal muscle phenotype and mitochondrial and lipid content remains controversial, probably because physical activity, which greatly influences muscle physiology, is rarely accounted for. The present study was therefore designed to investigate the effects of ageing, physical activity, and pre-frailty on skeletal muscle phenotype, and mitochondrial and intramyocellular lipid content in men.MethodsRecreationally active young adult (20-30?yo; YA); active (ACT) and sedentary (SED) middle-age (50-65?yo; MA-ACT and MA-SED); and older (65?+?yo; 65?+?ACT and 65?+?SED) and pre-frail older (65?+?PF) men were recruited. Muscle biopsies from the vastus lateralis were collected to assess, on muscle cross sections, muscle phenotype (using myosin heavy chain isoforms immunolabelling), the fibre type-specific content of mitochondria (by quantifying the succinate dehydrogenase stain intensity), and the fibre type-specific lipid content (by quantifying the Oil Red O stain intensity).ResultsOnly 65?+?SED and 65?+?PF displayed significantly lower overall and type IIa fibre sizes vs. YA. 65?+?SED displayed a lower type IIa fibre proportion vs. YA. MA-SED and 65?+?SED displayed a higher hybrid type IIa/IIx fibre proportion vs. YA. Sedentary and pre-frail, but not active, men displayed lower mitochondrial content irrespective of fibre type vs. YA. 65?+?SED, but not 65?+?ACT, displayed a higher lipid content in type I fibres vs. YA. Finally, mitochondrial content, but not lipid content, was positively correlated with indices of muscle function, functional capacity, and insulin sensitivity across all subjects.ConclusionsTaken altogether, our results indicate that ageing in sedentary men is associated with (i) complex changes in muscle phenotype preferentially affecting type IIa fibres; (ii) a decline in mitochondrial content affecting all fibre types; and (iii) an increase in lipid content in type I fibres. They also indicate that physical activity partially protects from the effects of ageing on muscle phenotype, mitochondrial content, and lipid accumulation. No skeletal specific muscle phenotype of pre-frailty was observed.

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Lower physical activity is associated with skeletal muscle fat content in girls.

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Lower physical activity is associated with skeletal muscle fat content in girls.

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