Growth factors, muscle function and doping

Departments of Surgery, Anatomy and Developmental Biology, Royal Free and University College Medical School, University of London, Rowland Hill Street, London NW3 2PF, UK.
Current Opinion in Pharmacology (Impact Factor: 4.6). 07/2008; 8(3):352-7. DOI: 10.1016/j.coph.2008.02.002
Source: PubMed


Recently much interest has been shown in developing a treatment of muscle wasting associated with a range of diseases as well as in ageing, which are major medical and socioecomonic problems. Emerging molecular techniques have made it possible to gain a better understanding of the growth factor genes involved and how they are activated by physical activity including the IGF-I gene that can be spliced to give rise to different isoforms, one of which is called MGF that activates muscle progenitor cells that provide the extra nuclei required for muscle hypertrophy, repair and maintenance. This fact that MGF 'kick starts' the hypertrophy process clearly has potential for abuse and has already attracted the attention of body builders.

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    • "scle hypertrophy following BFR training . There is recent evidence indicating that elevations of local - ized hormones may play some role in the hypertrophic response . Mechano growth factor ( MGF ) is locally increased in response to both mechanical stimuli and cellular damage , providing a potential mechanism for skeletal muscle hypertro - phy ( Goldspink et al . , 2008 ) . Interestingly , using an animal model in which the insulin - like growth factor 1 receptor was knocked out , animals were still able to undergo significant muscle hypertrophy ( Spangenburg et al . , 2008 ) . This finding supports Hornberger et al . ( 2004 ) who have observed increased activation of the mTOR pathway in response to me"
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    ABSTRACT: Although evidence for high-intensity resistance training-induced muscle hypertrophy has accumulated over the last several decades, the basic concept of the training can be traced back to ancient Greece: Milo of Croton lifted a bull-calf daily until it was fully grown, which would be known today as progressive overload. Now, in the 21st century, different types of training are being tested and studied, such as low-intensity exercise combined with arterial as well as venous blood flow restriction (BFR) to/from the working muscles. Because BFR training requires the use of a cuff that is placed at the proximal ends of the arms and/or legs, the BFR is only applicable to limb muscles. Consequently, most previous BFR training studies have focused on the physiological adaptations of BFR limb muscles. Muscle adaptations in non-BFR muscles of the hip and trunk are lesser known. Recent studies that have reported both limb and trunk muscle adaptations following BFR exercise training suggest that low-intensity (20-30% of 1RM) resistance training combined with BFR elicits muscle hypertrophy in both BFR limb and non-BFR muscles. However, the combination of leg muscle BFR with walk training elicits muscle hypertrophy only in the BFR leg muscles. In contrast to resistance exercise with BFR, the exercise intensity may be too low during BFR walk training to cause muscle hypertrophy in the non-BFR gluteus maximus and other trunk muscles. Other mechanisms including hypoxia, local and systemic growth factors and muscle cell swelling may also potentially affect the hypertrophic response of non-BFR muscles to BFR resistance exercise.
    Clinical Physiology and Functional Imaging 07/2012; 32(4):247-52. DOI:10.1111/j.1475-097X.2012.01126.x · 1.44 Impact Factor
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    • "One explanation might be due to the localized production IGF- 1Ec, better known as mechano growth factor (MGF). MGF is locally increased in response to both mechanical stimuli and cellular damage , providing a potential mechanism for skeletal muscle hypertrophy [44]. However, Hornberger et al. [45] have observed increased activation of the mammalian target of rapamycin (mTOR) pathway, independent of locally activated growth factors, in response to mechanical stimulation (passive stretch). "
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    ABSTRACT: Traditionally it has been thought that muscle hypertrophy occurs primarily from an overload stimulus produced by progressively increasing an external load using at least 70% of one's concentric one repetition maximum (1RM). Blood flow restricted exercise has been demonstrated to result in numerous positive training adaptions, specifically muscle hypertrophy and strength at intensities much lower than this recommendation. The mechanisms behind these adaptions are currently unknown but a commonly cited concept is that acute elevations of systemic hormones, specifically growth hormone (GH), play a large role with resistance training induced muscle hypertrophy, possibly through stimulating muscle protein synthesis (MPS). We hypothesize that the alterations in the intramuscular environment which results in the rapid recruitment of FT fibers, is the large driving force behind the skeletal muscle hypertrophy seen with blood flow restriction, whereas the external load and systemic endogenous hormone elevations may not be as important as once thought. It is further hypothesized that although skeletal muscle hypertrophy can be achieved at low intensities without blood flow restriction when taken to muscular failure, the overall volume of work required is much greater than that needed with blood flow restriction.
    Medical Hypotheses 08/2011; 77(5):748-52. DOI:10.1016/j.mehy.2011.07.029 · 1.07 Impact Factor
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    • "Future experiments will investigate if this approach is also efficient in muscle of constitutive KO mice. Furthermore , since XLMTM muscle is characterized by the presence of hypotrophic fibres, one may speculate that therapies aiming at increasing muscle mass, such as myostatin blockage and insulin-like growth factor (IGF1) overexpression [23], may also be beneficial for patients. "
    Neuromuscular Disorders 09/2009; 19(10):721-9. DOI:10.1016/j.nmd.2009.06.373 · 2.64 Impact Factor
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