Body Systems


How the Body is Impacted by Exercise at 50% Intensity to 100% Intensity 


When the body moves from resting state to 50% effort the bodies muscles must adjust. Muscles need more blood to deliver blood glucose for energy. When the muscles are moving at 50% effort oxygen can be utilized in glycolisys and in the Kreb Cycle. As the muscles use the muscle glucose/glycogen more is produced by these cycles. Fat oxidation can occur when oxygen is present as well. This is when fat is broken down into glucose. This process leaves the body with the most calories to burn. As levels of muscle glucose begin to become low, the liver then releases glucose. These processes deliver enough energy for continuous exercise. As the body moves from 50% to 100% these process listed above can not still be used. More quick energy is required. Phosphogen systems take over. These systems use an abundance of energy, more than the body can produce. In turn, the muscles begin to accumulate lactic acid. Lactic acid prohibits oxygen from coming into the muscle, which will in turn, will force the body to shut down eventually. The phosphogen system does not make near as much energy. The energy I’m referring to is ATP. Fast glycolysis produces 2 ATP while the Oxidative system produces 38 ATP. 


As the body moves from a resting state to 50% many things happen in the cardiovascular system. Oxygen consumption increases, which causes the body to increase respiration. Blood pressure then begins to rise along with stoke volume. The heart rate increases to keep up will the oxygen need as well. The left ventricle begins to pump blood throughout the body. (Trained athletes are known to have large left ventricles) Oxygen exchange in the aveolis increase. Breathing rate increases to keep up with the need of oxygen. 



Endocrine levels are also effected by an increase in exercise. At first the body begins increasing catecholamine which is the fight or flight hormone in the sympathetic nervous system. As intensity increases norepinephrine and epinephrine increase. These affects increase less after training. The body also begins to release cortisol which sometimes has adverse effects on muscle growth and strength gains when strength training. An abundance of cortisol can also make muscles more sore after a workout. With training this response will not be as severe though. With an increase in exercise the thyroxine turnover also increases. The thyroid gland plays a major factor in weight. The more active a person is the better their thryroid gland will perform, and the less active a person is the worse it will perform. Testosterone is another hormone that is effected with intensity of training. Test levels will rise with heavy training and will remain generally the same when training at a submaximal level. Insulin is another hormone that is effected when training. As the body increases intensity more insulin is needed to deliver glucose to muscle tissue. As levels equal out, glucagon is then released to force insulin to not cause adverse effects. These two hormones work hand in hand to maintain healthy levels of glucose in the blood. Finally, as intensity peaks ADH increases to prevent dehydration. ADH increases water retention. 


Metabolism is broken down into two categories: aerobic and anaerobic. Aerobic metabolism is associated with lower intensity levels such as the first part of the question, 50% intensity. Anaerobic metabolism is associated with levels of intensity such as 100% intensity. At 50% intensity aerobic processes will be used. This is where oxygen is still present. Oxidative processes will produce 38 ATP and can be maintained for long durations of time. Glucose can be used from the muscle and the liver. After glucose levels drop Glycogenisis will begin along with the Kreb Cycle, Corri Cycle, and Electron Transport System. These processes are carried out in the Mitochondria. With training at this level of intensity the Mitochondria will actually increase in size and work more efficiently. Each of these processes produces plenty of ATP to keep up with body’s demands. At 100% intensity anaerobic process will be used. Here the intensity is too high for the body to maintain proper function for long durations of time. 100% intensity can only be maintained for short durations. Lactic acid will build and prevent oxygen from entering the muscle cells. Here ATP is used rapidly. With rest though, glucose levels will be replenished. At 100% intensity levels interval training is used so that the body can maintain this work load. 


The nervous system reacts as does all the other body systems to exercise intensity. When the body begins exercise the parasympathetic nervous system begins moving towards the back burner as the sympathetic nervous system begins moving towards the front burner. The fight or flight nervous reactions are very important when thinking of the sympathetic nervous system. The body sends signals from the brain down the spine and into vast amounts of nerve ending that are throughout the body. One way the nervous system reacts with exercise is by increasing activity in the SA node, which increases the heart rate. As intensity increases the SA node is more active. A big part of the nervous system that can help prevent injury is the Golgi Tendon Organelle. This part of the nervous system will cause the muscle to shut down when it has had to much load and will prevent the muscle from tearing or moving past workable loads.

Once you have learned about your body and how it works, you will be able to optimize your workout routines.