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( Hyon Park ),( Roger P. Farrar ) 한국스포츠정책과학원(구 한국스포츠개발원) 2002 International Journal of Applied Sports Sciences Vol.14 No.1
Female Sprague Dawley rats were divided into two main groups, lab chow or lab chow with 2% ß-guanidinopropionic acid(ß-GPA). Each main group was subdivided into four chronic low-frequency electrical stimulation(CLFES) groups of 0, 3, 14, or 28 days. Following this treatment the plantaris muscle was evaluated for changes in biochemical properties. There was an increase in oxidative capacity as evidenced by a 200% increase in citrate synthase(CS) and cytochrome oxidase(COX) activity. The mitochondrial RNA processing endonuclease RNA(MRP-RNA) increased by 500% with just 3 days of stimulation and remained at this level or decreased slightly over the rest of the stimulation period. Creatine depletion by feeding ß-GPA induced an 100% increase in CS and COX activity which rose to a 180% increase with CLFES. While CLFES induced a rise in CS and COX which was preceded by elevation in MRP-RNA, creatine depletion alone did not elevate MRP-RNA, yet stimulated an increase in enzyme activity. The level of mRNA for CS and COX subunit III were mainly affected by the application of electrical stimulation, not by chronic creatine depletion. CLFES induced a transformation to more oxidative fibers which was greater in magnitude than the creatine depletion alone, but less than the interaction of CLFES upon ß-GPA fed rats. These data demonstrate that specific challenges to homeostatic balance within skeletal muscle use specific alterations in pre-translational, translational, and post-translational regulation to achieve their adaptive response.
Adaptability of Skeletal Muscle to Resistance Training
Lee Sukho,Roger, P.Farrar 한국운동영양학회 2003 Physical Activity and Nutrition (Phys Act Nutr) Vol.7 No.1
Skeletal muscle comprises 40-45% of the mass of the body of a health individual (Rooyacker et al., 1997). The functional demands placed upon skeletal musele vary greatly throughout the day, from repetitive tasks against very low resistance, to explosive powerful contraction against very high resistance. Training for athletic competition takes advantage of the muscle's ability to adapt to the functional demands placed upon it over weeks and years of training. Critical to the adaptation produced is the manner in which the muscle is trained, whether it be repeated contractions against relative light loads muscle mass. Due to the fact that many of the most popular sports in the world, such as soccer, basketball, baseball, and football require intermittent bursts of very powerful movements, there is a great interest in increasing muscle mass. Maximal force is directly cross sectional area of muscle and maximal power is derived from the maximal force that can be developed per unit of time, usually in terms of milliseconds. Over the years many researchers have attempted to develop models to better understand how the alterations of mechanical load and hormonal milieu might optimize increases in muscle mass and concomitant increases in power. This article will primarily focus on animal models that have been utilized to increase muscle mass. Included in this review will be models that elevated mechanical load upon skeletal muscle, either chronically or intermittently, as well as the influence of IGF-1, a hormone that has both a myogenic and mitogenic efect upon skeletal muscle.
( Suk Ho Lee ),( Roger P. Farrar ) 한국스포츠정책과학원(구 한국스포츠개발원) 2003 International Journal of Applied Sports Sciences Vol.15 No.1
Insulin-like growth factor-1 (IGF-1) has been shown to play a major role in development of skeletal muscle. Resistance training is frequently used as an intervention for inducing hypertrophy in skeletal muscle. The purpose of this study was to examine the effects of a combination of overexpression of IGF-l and resistance training on skeletal muscle mass and junction. Male C57BL/6 mice were injected in the posterior compartment of their left lower leg with a recombinant adeno-associated virus, which was constructed with the IGF-1 gene linked to the myosin light chain promoter. After 8 weeks of viral injection, the mice were divided into two main groups, sedentary control and resistance training. These main groups were subdivided into four groups based on each leg, control (CON), IGF, RT (resistance training) and RT+IGF. The mice in the resistance training group were trained one training period per day every third day for 8 weeks using ladder climbing. Resistance training resulted in a 15.1 % increase in muscle mass of the flexor hallucis longus (FHL) in mice. We also observed 7.8% increases in the muscle mass of FHL treated with recombinant adeno associated virus expressing IGF-1 itself. IGF-1 overexpressed FHL muscle demonstrated an appearance of central nuclei indicating ongoing regeneration. There was a 24.6% increase in muscle mass of the FHL with the combined interventions compared to the control level. Therefore, the combination of resistance training and overexpression of IGF-1 induces greater hypertrophy than either treatment alone. This result suggests that a combination of resistance training and overexpression of IGF-1 could be an effective treatment for inducing hypertrophy.