Found this interesting study while doing research for the anabolism thread, thought I'd post it for fun.



1: PLoS ONE. 2008 Jan 2;3(1):e1385. Links
Sex-related differences in gene expression in human skeletal muscle.Welle S, Tawil R, Thornton CA.
Department of Medicine, University of Rochester, Rochester, New York, United States of America.

There is sexual dimorphism of skeletal muscle, the most obvious feature being the larger muscle mass of men. The molecular basis for this difference has not been clearly defined. To identify genes that might contribute to the relatively greater muscularity of men, we compared skeletal muscle gene expression profiles of 15 normal men and 15 normal women by using comprehensive oligonucleotide microarrays. Although there were sex-related differences in expression of several hundred genes, very few of the differentially expressed genes have functions that are obvious candidates for explaining the larger muscle mass of men. The men tended to have higher expression of genes encoding mitochondrial proteins, ribosomal proteins, and a few translation initiation factors. The women had >2-fold greater expression than the men (P<0.0001) of two genes that encode proteins in growth factor pathways known to be important in regulating muscle mass: growth factor receptor-bound 10 (GRB10) and activin A receptor IIB (ACVR2B). GRB10 encodes a protein that inhibits insulin-like growth factor-1 (IGF-1) signaling. ACVR2B encodes a myostatin receptor. Quantitative RT-PCR confirmed higher expression of GRB10 and ACVR2B genes in these women. In an independent microarray study of 10 men and 9 women with facioscapulohumeral dystrophy, women had higher expression of GRB10 (2.7-fold, P<0.001) and ACVR2B (1.7-fold, P<0.03). If these sex-related differences in mRNA expression lead to reduced IGF-1 activity and increased myostatin activity, they could contribute to the sex difference in muscle size.

PMID: 18167544 [PubMed - in process]

PMCID: PMC2148100


I'll be doing some background research on Activin receptor IIB just for fun as well as GRGB10 in the anabolism thread. Cheers

Gender impacts the post-exercise substrate and endocrine response in trained runners

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J Int Soc Sports Nutr. 2008 Feb 26;5(1):7 [Epub ahead of print]Click here to read Links
Gender impacts the post-exercise substrate and endocrine response in trained runners.
Vislocky LM, Gaine PC, Pikosky MA, Martin WF, Rodriguez NR.

ABSTRACT: BACKGROUND: Although several studies have investigated gender differences in the substrate and endocrine responses during and following endurance exercise, few have studied sex differences during a more prolonged recovery period post endurance exercise. The purpose of this study was to compare and characterize the endocrine and substrate profiles of trained male and female adult runners during the three-and-a-half hour recovery period from an endurance run. METHODS: After consuming a euenergetic diet (1.8 gA.kg-1A.d-1 protein, 26% fat, 58% carbohydrates, 42.8 A+/- 1.2 kcal/kg body weight) for 8 days, blood was collected from trained male (n = 6, 21 yrs, 70 kg, 180 cm, 9 % body fat, VO2peak 78.0 A+/- 3.4 mLA.kg FFM-1A.min-1) and female (n = 6, 23 y, 66 kg, 170 cm, 29% body fat, VO2peak 71.6 A+/- 4.5 mLA.kg FFM-1A.min-1) endurance runners at rest and during recovery from a 75 min run at 70% VO2peak. Circulating levels of glucose, lactate, free fatty acids (FFAs), insulin, cortisol, growth hormone (GH), and free insulin-like growth factor I (IGF-I) were measured. RESULTS: During the recovery period, females experienced increases in glucose, lactate and insulin while no changes were noted in men (P < 0.05). Males experienced increases in GH and decreases in IGF-I levels respectively (P < 0.05) while no changes were observed in females. FFA levels increased during recovery from endurance exercise, but changes were not different between genders. CONCLUSIONS: These data further document gender differences in substrate and endocrine changes during a prolonged recovery period following endurance exercise. Future studies are needed to evaluate the effect of differing diets and nutritional supplements on these gender-specific post-exercise substrate and endocrine differences.

Sex differences in contractile properties and fatigue resistance of human skeletal mu

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Exp Physiol. 2008 Feb 22 [Epub ahead of print]Click here to read Links
Sex differences in contractile properties and fatigue resistance of human skeletal muscle.
Wust RC, Morse CI, de Haan A, Jones DA, Degens H.

IRM, MMU.

To explore the cause of higher skeletal muscle fatigue resistance in women than men, we used electrically evoked contractions (1-s on 1-s off, 30 Hz, 2 min), which circumvents motivational bias and allows examination of contractile properties. We compared 29 men (26.5 (7.0) yr) (mean (SD)) with 35 women (25.4 (7.6) yr). Strength of the quadriceps muscle was higher in men than women (P<0.001). The lower maximal rate of relaxation in women (P=0.002) indicates that their muscles were slower than those of men. The torque declined less in women than in men (37.7 (10.7)% vs. 29.9 (10.0)%; P=0.002), and was not related to muscle strength or size, as determined with MRI. The sex-difference in fatigability was also seen when the circulation to the leg was occluded (torque declined 76.9 (10.8) vs. 59.5 (16.9)% in men vs. women respectively; P=0.008). The maximal rate of relaxation correlated with the fatigability of the muscle under all conditions (correlations ranging from 0.34 to 0.51, P<0.02). We conclude that the sex-related difference in skeletal muscle fatigue resistance is not explicable by differences in motivation, muscle size, oxidative capacity and/or blood flow between sexes, but might be related to differences in fiber type composition.

Sex Differences in Exercise Metabolism and the Role of 17-Beta Estradiol

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Med Sci Sports Exerc. 2008 Feb 29 [Epub ahead of print]

Sex Differences in Exercise Metabolism and the Role of 17-Beta Estradiol.

Tarnopolsky MA.

Department of Pediatrics and Medicine, McMaster University, Hamilton, CANADA.

Women oxidize more lipid and less carbohydrate and protein compared with men during endurance exercise. The increase in fat oxidation is associated with higher intramyocellular lipid content and use as well as greater adipocyte lipolysis. Glucose rates of appearance and disappearance are lower for women than for men, with no change in basal muscle glycogen, and some evidence for muscle glycogen sparing during endurance exercise. Women oxidize less protein compared with men and show lower leucine oxidation during exercise. The consistent and robust finding of higher mRNA abundance for most components of fat-oxidation pathways in women compared with men is directionally consistent with the substrate-oxidation data. A lack of directional consistency between mRNA species involved in carbohydrate and protein metabolism and the known sex differences during exercise implies that fatoxidation is regulated and that carbohydrate and protein oxidation follow by metabolic demand. Administration of 17-beta-estradiol to men recapitulates most of the described sex differences in metabolism and mRNA content. The greater fat oxidation for women during submaximal endurance exercise compared with men seems to occur partly through a sex hormone-mediated enhancement oflipid-oxidation pathways.