The Role of Dietary Protein Intake and Resistance Training on Myosin Heavy Chain Expression
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The Role of Dietary Protein Intake and Resistance Training on Myosin Heavy Chain Expression Colin D. Wilborn1 and Darryn S. Willoughby, FISSN1 Exercise and Biochemical Nutrition Laboratory, Baylor University, Waco, TX. Journal of the International Society of Sports Nutrition. 1(2):27-34, 2004. Address correspondence to [email protected]. Received November 15, 2004/Accepted December 20, 2004/Published (online) ABSTRACT During resistance training the muscle undergoes many changes. Possibly the most profound and significant changes are those that occur in the muscles contractile proteins. Increases in these contractile proteins are one of the primary factors contributing to myofibrillar hypertrophy. The most abundant muscle protein is myosin, which comprises 25% of the total muscle protein. Due to the large amount of skeletal muscle that is composed of myosin, changes in this fiber may have profound effects on skeletal muscle size and strength. The myosin molecule is made up of 6 subunits, 2 very large heavy chains, and 4 smaller light chains. The myosin heavy chain (MHC) accounts for 25 -30% of all muscle proteins making its size an important factor in skeletal muscle growth. In conjunction with resistance training, dietary protein intake must be adequate to illicit positive adaptations. Although many studies have evaluated the role of dietary protein intake on skeletal muscle changes, few have evaluated the MHC specifically. Research has clearly defined the need for dietary protein and resistance training to facilitate positive changes in skeletal muscle. The purpose of this review was to evaluate the current literature on the effects of dietary protein and resistance training on the expression of the myosin heavy chain. Journal of the International Society of Sports Nutrition. 1(2):27-34, 2004 Key Words: Muscle Fiber, Contractile Protein, Protein Synthesis INTRODUCTION A combination of resistance training and proper diet elicits several physiological responses that enhance the structure and function of skeletal muscle. Research has clearly defined the benefits of resistance training (i.e., increased muscular endurance, strength, power, increased metabolism, decreases in body fat, etc) 1-3 . However one of the most profound changes seen is muscular hypertrophy, or more specifically myofibrillar and sarcoplasmic hypertrophy. Sarcoplasmic hypertrophy involves the growth of the sarcoplasm and non-contractile proteins (α-actinin, desmin, dystrophin, myomesins, nebulin, titin, and vinculin) that
do not directly contribute to muscular force production 4, 5 . Filament area density decreases while cross-sectional area increases, without a significant increase in strength. Myofibrillar hypertrophy occurs due to increases in the number of myosin/actin filaments inside each sarcomere. This leads to increased strength and size of the contractile unit (actin, myosin, troponin, and tropomyosin) of muscle. The focus of this review will be the contractile components. These contractile components within each muscle fiber mak
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