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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: 4.23). 07/2008; 8(3):352-7. DOI: 10.1016/j.coph.2008.02.002
Source: PubMed

ABSTRACT 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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    • "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. "
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    ABSTRACT: Muscle fibers can generally be divided into slow and fast twitch according to their contraction speed. Even though an individual normally has the same ratio of slow/fast muscle fibers throughout his or her body, the lower-limb muscles are predominantly designed to provide the maximum dynamic output in rapid movements (e.g., jumping). The limited data on dancers’ muscle profiles have shown that (ballet) dancers have predominately slow fibers. Muscular strength, together with aerobic and anaerobic capacity, joint mobility and muscle flexibility, and body composition form the continuum of physical fitness. Strength is defined as the maximum force that a muscle group can generate at a specified velocity; its levels can be affected by several factors. which include age, gender, type of muscle fiber, nutrition, and body temperature. There is no scientific evidence suggesting that different strength training regimens should be employed for the different styles of dance. However, reduced muscular strength has been associated with greater severity of injury in dancers. Poor aerobic capabilities, high ectomorphy ratings with low percent body fat values, and the biomechanics of different dance techniques have also been identified as underlying sources of injury in dancers. The most common location for injury in ballet dancers is the foot and the ankle, while in contemporary dancers it is the low back and knee. Little information is available with respect to other dance styles.
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