In addition, androgens also have anabolic actions on several extragenital structures including muscle and bone . These genes encode muscle-specific transcription factors, enzymes, structural proteins, as well as microRNAs. Mechanisms of testosterone's sexually dimorphic epigenetic and tissue-specific activational effects and roles of α-keto reductase and steroid 5α-reductase and 1-carbon and polyamine metabolism in testosterone's actions remain poorly understood. The conversion of testosterone to 5α-DHT is not required for mediating its anabolic effects. Testosterone improves muscle bioenergetics by increasing erythrocytes, oxygen availability, tissue blood flow, and mitochondrial mass and quality. But what about the risk of low testosterone levels? Don’t be tempted by increasing your testosterone for muscle gain - you need to actually put the work in. However, other groups found no direct effects of testosterone on C2C12 proliferation, nor on cultured porcine satellite cells 54, 55. Many factors, such as nitric oxide , interleukin-6 , and Notch signaling 43–45, may contribute to satellite cell activation but the exact underlying molecular mechanisms and interferences by androgens remain to be identified. Satellite cells are located between the basal lamina and the plasma membrane of muscle fibers . During growth and repair of the adult skeletal muscle, quiescent tissue-specific progenitor cells, also called satellite cells, are activated and start proliferating, at which stage they are often referred to as myoblasts . Thus, differences in AR protein content of skeletal muscles seem to underlie differences in androgen responsiveness. To what extent anabolic androgen action is mediated directly through the AR of the different muscular cells or indirectly through other cells or tissues that affect muscle physiology, also remains an important research question. Although micro trauma does occur during resistance training, it correlates poorly with the magnitude of hypertrophy. The precise relation between microtrauma and muscle growth is not entirely understood yet.citation needed Cortisol decreases amino acid uptake by muscle tissue, and inhibits protein synthesis. Vanderschueren are, respectively, senior clinical investigators of the Fund for Scientific Research Flanders (FWO) and the University hospital of Leuven. V. Dubois is holder of a doctoral fellowship of the Fund for Scientific Research Flanders (FWO). Which pathways can safely be used in therapeutic strategies for the treatment of disease or age-related muscle wasting? What are the main cellular targets under normal physiological as well as clinical conditions? Recently, Dalton et al. have reported a phase II clinical trial where GTx-024, an orally available nonsteroidal SARM, has been tested in healthy elderly men and postmenopausal women. The scale measures gravity, it does not measure what you are made of, i.e., your body composition, and how it changes over time. There is a body composition crisis happening in women over 35 that mainstream medicine is almost entirely ignoring, and the bathroom scale is part of the reason. On the other hand, very rapid tempos shorten TUT and reduce the stimulus a muscle receives for hypertrophic adaptation. The literature suggests that moderate tempos give the best results for hypertrophy (between 2 and 8 seconds), while extremely slow tempos may restrict hypertrophy by limiting the amount of load that can be lifted, limiting progressive overload. A study done by Burd et al. (2012) showed that at relatively light loads (30% of best effort). Time under tension (TUT) is the duration of time that the muscle being trained is stressed during a repetition. that consistent anaerobic strength training will produce hypertrophy over the long term, in addition to its effects on muscular strength and endurance. Mechanical tension activates mechanosensitive pathways, including mTOR signaling, which increases muscle protein synthesis and contributes directly to hypertrophy.|Androgens also interfere with other signaling pathways , and several non-genomic androgen effects are described . The AR is a ligand-inducible transcription factor that binds to specific DNA sequences called androgen response elements (AREs) and recruits coactivators, which will help affect the transcription of target genes . While there is uncertainty about which measures of muscle performance are androgen-responsive , the tests of physical function used in most of the trials have serious limitations. In addition, anabolic action of androgens is partly established through crosstalk with other signaling molecules such as Akt, myostatin, IGF-I, and Notch. Testosterone increases blood flow by nongenomic mechanisms involving nitric oxide production and calcium and potassium channels in vascular smooth muscle. Famed as the fuel behind strength, sex, masculinity, and fertility, testosterone makes men perform at their best. Dr Luke Pratsides is a General Practitioner working in the NHS, with a background in clinical leadership across digital health.|Moreover, the fact that IGF-I induces expression, phosphorylation, nuclear translocation and DNA binding activity of the AR in muscle 160, 161 indicates the existence of a feedback-loop between IGF-I and androgens. Collectively, these data indicate that androgens interfere with the muscular IGF-I system at different levels. The ribosomal protein kinase p70s6k is a downstream effector of IGF-I participating in the regulation of protein turnover in skeletal muscle . A study investigating the effect of androgens on the phosphorylation of p70s6k provided further evidence that the muscular IGF-I system plays an important role in anabolic androgen action. IGF-IEa levels decreased upon orchidectomy both in LA and gastrocnemius muscle, while MGF levels remained constant , so IGF-IEa but not MGF expression is androgen-dependent in both perineal and limb muscles. There is increasing evidence that, in contrast to the circulating hormone, locally produced IGF-I is an important mediator of androgen action in muscle.|The study concluded that more than 30 g of protein in a single meal did not further enhance the stimulation of muscle protein synthesis in young and elderly. The additional contractile proteins appear to be incorporated into existing myofibrils (the chains of sarcomeres within a muscle cell). Collectively, the evidence suggests that eccentric contractions can produce substantial muscle hypertrophy due to the high force production and unique molecular signaling.It might not be superior to concentric training if matched for total load and reps.citation needed Overall, while TUT has shown some positive benefits in terms of muscle growth, long-term hypertrophy seems to depend more on total training volume and progressive overload than on repetition duration only.}
