can be incredibly useful. There are two di erent types of muscular growth that you can use to your advantage with a bit of inside knowledge. The names of both sound complicated--myo brillar and sarcoplasmic--but the di erence is really very simple. Let's start with a basic primer on muscle fibers. Every muscle ber has two main parts: myo brils, which are cylinder- shaped laments that contract to create movement, and the sarcoplasm, which is the uid surrounding the myo brils that contains glycogen stores and mitochondria to provide energy (ATP). Myofibrillar hypertrophy20 can be thought of as growth for maximal strength. The myo brils in the muscle ber increase in number, adding primarily strength and some size to the muscle. This kind of muscle growth is achieved by high tension--doing one to ve reps at 8090% of your one-repetition maximum, for example. The strength output is limited to brief intervals, as
critical; available ATP must remain above 10 Chapter 1 approximately 30% of the resting stores, or with ATP (100 mmol/kg dry muscle weight relaxation cannot occur. This is because for phosphocreatine compared with 25 mmol/ relaxation of contraction is dependent on kg dry muscle weight for ATP) but very low ATP, which is especially important because abundance compared with glycogen (500 removal of calcium from the sarcoplasm is mmol/kg dry muscle weight for glycogen). an ATP-dependent process (Hargreaves and Phosphocreatine can easily transfer a phos- Thompson 1999). phate group to ADP in a reaction catalyzed The primary fuels for muscle cells include by creatine kinase. This reaction is easily phosphocreatine, glycogen, glucose lactate, reversible and phosphocreatine supplies free fatty acids, and triglycerides
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