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Exercise Physiology


1. Discuss the relationship between distribution of muscle fiber type and performance. How might exercise training modify or change a person’s fiber-type distribution?

Muscle fiber types is a subject that unfortunately is often a neglected one. Understanding what the different muscle fiber types are, how these fibers are activated, what type of fuels they use and how fast they recover will provide you with an understanding that will enable you to create a personalized program based on the goals that you want to achieve (Rivera 2017). According to Wilmore, there are four different types of muscle fibers: type I, type IIa, type IIb, and type IIc (Wilmore, 2008). The differences and relationship between distributions of muscles are described as follow:

· Type I is a single skeletal muscle contains fibers having different speeds of shortening and ability to generate maximal force also called slow-twitch fibers.

· Type IIa which is also called fast-twitch fibers. These fibers have much less blood flow in them, have a moderate tolerance to fatigue and can handle moderate amounts of work.

· Type IIb fibers have a speedy contraction and relaxation time, and produce increased amounts of force. They generate power through anaerobic means with low myoglobin content. Rivera (2017)

· Type IIc –they require oxygen as fuel and because of this, they are the ones most used in endurance type of sports like running, cycling, and cross country.

Type I fibers take approximately 110 ms to reach peak tension when stimulated whereas, Type IIa fibers can reach peak tension in about 50 ms (Wilmore, 2008); because the type IIa fibers have a quick contraction time, they create energy by both aerobic and anaerobic means with high myoglobin content. However, there is less blood flow in these fibers; they have a fair tolerance to exhaustion and can manage a reasonable amount of work. In Type IIb –these fibers have a very low tolerance to fatigue and need a high period of recovery after use.

Hypertrophy is when skeletal muscle cells chemically bind with type IIb fibers to create type IIc muscle fibers. Bodybuilders have the most of these type fibers; they add mass and structural support for the muscle. This muscle fiber can expand the characteristics of either the fast twitch or slow twitch fibers with proper training. On the average, most people have a distribution of 50% Type IIa fibers, 25% Type IIb and 25% Type IIc. However, the body has the capability to change these ratios based on the stimulus imposed” (Rivera, 2017).

2. Describe the mechanisms by which muscle glycogen is broken down to glucose for use in glycolysis.

Glucagon breaks down glycogen into glucose and this increases the absorption of glucose, which raises blood sugar. The changing of a particle of glucose to glucose-6-phosphate involves the disbursement or input of one ATP particle. During muscle glycogen break down the process of glycolysis releases ATP then glucose-6-phosphate is produced. Glycogen is the main energy substrate during exercise intensity above 70% of maximal oxygen uptake and fatigue develops when the glycogen stores are depleted in the active muscles (Jensen, 2011).

Glycogen Debranching Enzyme (GDE) is then used to convert alpha (1-6) branches of glycogen into alpha (1-4) branches, leaving a single glucose at each 1,6 branch. This enzyme acts on glycogen branches that have reached their hydrolysis limit with glycogen phosphorylase catalyst. Therefore, the main products of glycogen breakdown are G1Pmolecule and glucose. Apparently, this glucose can proceed to the glycolysis pathway, as G1P molecule proceeds to be broken down into glucose units. The third mechanism of glycogenolysis involves the conversion of G1P into glucose-6-phosphate (G6P) by Phosphoglucomutase enzyme (Richter et al. 2001).

3. Describe how a nerve impulse is transmitted along its axon.

The transmission of a nerve impulse along the axon involves a number of processes. The process starts when a stimulus is received by the dendrites, and then transmitted to the axon. Nerve impulses have a domino like effect. Each neuron is given an impulse and must deliver it to the next neuron and make sure the right impulse continues on its pathway. The dendrites (neuron particles) pick up an impulse that is transported through the axon and transmitted to the next neuron through a chain of chemical events. The impulse passes through a neuron in roughly seven milliseconds. Division of the neuron’s membrane takes place; sodium is on the outer surface, and potassium is on the inner surface. Moreover, at the axon terminal, the nerve impulse stimulates the axon terminal bundles to release neural transmitters into the synaptic gap, which then binds with proteins of the next neuron that is about to receive the impulse (Popov, 2014).

4. What are two advantages of fat over carbohydrate for fuel storage in the body?

Our body does not use more than 1.0-1.1g of consumed carbohydrate per minute, which provides only 240-264 kcal of energy. Body fat and carbohydrate stores provide the major sources of exercise fuel; whereas fat sources (plasma free fatty acids derived from adipose tissue and intramuscular triglycerides) are relatively plentiful, carbohydrate sources (plasma glucose derived from the liver or dietary carbohydrate intake, and muscle glycogen stores) are limited (Burke, 2004, pg. 15). Many researches shows that fats yield twice more energy compared to carbohydrates Therefore, fats help to provide body insulation against cold environmental temperatures.

5. Describe the primary structure of the heart and the primary functions of blood.

The heart is divided into separate right and left sections by the interventricular septum, or just the ‘septum’ when the context is obvious. Each of these (right and left) sections is also divided into upper and lower compartments known as atria and ventricles, The four main chambers of the heart are: Right Atrium, Right Ventricle, Left Atrium, Left Ventricle (IvyRose Health 2017). 

Deoxygenated blood (from the body) is pumped through the right atrium and the right ventricle (to the lungs), while oxygenated blood (from the lungs) is pumped through the left atrium and the left ventricle “to the body” (IvyRose Health 2017).

· Deoxygenated blood enters the right atrium from the superior vena cava and the inferior vena cava.

· Deoxygenated blood leaves the right ventricle by pulmonary artery, which takes blood to the lungs via the right and left brances of the pulmonary artery.

· Oxygenated blood enters the left atrium from the pulmonary veins. 
These may be labelled as ‘right pulmonary veins’ and ‘left pulmonary veins’.

· Oxygenated blood leaves the left ventricle by ascending aorta, which takes blood to the body via its system of arteries, arterioles, and capillaries. Major arteries leading from the heart (via the ascending aorta) include the brachiocephalic artery, the left common carotid artery, and the left subclavian artery (illustrated above). These are just a few of the main arteries of the body.

It is essential that blood flows in the correct direction through the heart so the structure of the heart includes a series of valves (IvyRose Health 2017).

Three primary functions of blood are “it transports a range of chemicals such as oxygen, carbon dioxide, hormones, and many others to various organs. The blood is responsible for the protection from different diseases and infections, since it contains platelets, white and red blood cells, and plasma. The blood also regulates a steady internal body environment by regulating the osmotic temperature and pressure inside the body ((Iaizzo, 2009).


Burke, L. (2004). Carbohydrates and Fat for Training and Recovery. Journal of Sports and

Sciences. Retrieved from:

Iaizzo, P. A. (2009). Handbook of Cardiac Anatomy, Physiology, and Devices. New York, NY: Springer. Retrieved from:

Jensen, J. (2011). The Role of Skeletal Muscle Glycogen Breakdown for Regulation of Insulin

Sensitivity by Exercise. Frontiers in Physiology. Retrieved from:

Rivera, H. (2017). Muscle Fiber Types and How They Relate to Your Training Program. Retrieved from:

Wilmore, J. Costill, D. & Kenney, W. (2008). Physiology of Sport & Exercise (5th ed.)

Champaign, IL: Human Kinetics

Richter, E. A et al. (2001). Skeletal muscle glucose uptake during dynamic exercise in humans: role of muscle mass. Am. J. Physiol. 254: E555–E561.

Popov V., (2014). Transmission of nerve impulse along the axon, Retrieved from,

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