The musculosketal and energy system
Response to acute exercise
The musculoskeletal system has muscles, tendons, ligaments, bones and cartilage. They support your body and enable you to move. They operate under the control of the nervous system and cause muscles to contract. When a muscle contracts it shortens pulling on the bone to which it is attached. The skeletal system forms the framework of the body, while muscles form the fleshy part. They facilitate movement, maintain posture and produce heat. When you start to exercise there is an increase blood suply to the muscles and a increase in temperature. This is because the metobolic activity is greater and therefore the demand for oxygen in more. The warming of your muscles in activity makes them more piliable and reduces risk of injury. The short term effects of exercise on your skeletal system are demonstrated by changes within the joint. Movement of joints stimulates the secretion of synovial fluid. This fluid also becomes less viscious and the range of movement at the joint increases. Also when you exercise your muscles are put under stress to the point where little tears occur in the muscles. These tears cause swelling in the muscles which causes pressure on the nerve which cause pain. Training improvements will only be made if the body has sufficient fuel and rest to repair these tears, making the muscle a little bit stronger than it was before.
All the movement people do needs energy. The the body generates energy in different ways depending on the intensity and duration of the activity. Activities that people do in short bursts and do intensively such as sprinting requires energy quickly. Whereas activities like marathon running requires large amounts of continued energy. The energy needed is provided through three different systems. These are ATP-PC, lactic acid system and aerobic system. The ATP-PC system resynthesises ATP when the enzyme creating kinase detects high levels of ADP. It breaks down the phosphocreatine to phosphate and creatine releasing energy. This then converts ADP to ATP in a coupled reaction in the lactic acid system carbohydrates in the diet are digested to glucose and stored in the muscles and liver as glycogen. Before glycogen can be used to provide energy to make ATP, it has to be converted to glucose. This process is called glycolysis. The glucose is broken down into two molecules of pyruvic acid. Then because of the absence of oxygen lactic acid is formed from the pyruvic acid. The stages for the aerobic system are the same as the lactic acid system in that glycogen is broken down into glucose 6- phosphate and then pyruvic acid. However under anaerobic conditions pyruvic acid is converted into fatigue inducing lactic acid by the enzyme lactate dehydrogenease. Under the aerobic conditions the pyruvic acid difusses into the matrix of the mitochondria forming acetyl coA. A complex cycle of reactions occurs in a process known the krebs cycle. Structures in the cells manufacture energy for ATP resynthesis by faciliting the many chemical reactions required to completely break down the stores of glycogen and fats to ensure a continous supply of energy.
During exercise your muscles contract and require a continual supply of nutrients and oxygen to support energy production. These requirements are above those required to support normal activities at rest. Your heart rate has to increase and beat harder and faster to meet the demands. Heart rate will increase in direct proportion to the intensity of the activity. Therefore the higher the intensity the faster your heart will beat. If these oxygen demands are met your heart rate will plateau and reach a steady state. Before the start of your exercise your heart rate is usually above resting levels, this is called the anticipatory rise and is a result of adrenalin. The best anticipatory heart rate response is observed in short sprint activities. When you exercise more blood goes to the muscles and less goes to other organs like the gut and liver. During exercise the blood flow to the active muscles increases because of the vasodilation of arterioles, involving an increase in the diameter of the blood vessels and resulting in an increased blood flow to the muscles. During exercise the blood flow to the liver and gut is decreased due to vasoconstriction of arterioles supplying those organs. Blood pressure is the pressure of blood against the walls of your arteries and results in two forces. One is created by your heart as it pumps blood around your arteries and into your circulatory system. The other force is the arteries as they resist blood flow. During aerobic exercise systolic blood pressure increases in proportion to the intensity while diastolic blood pressure stays the same. During anaerobic exercise both systolic and diastolic blood pressures increase significantly.
Your body is suprisingly insensitive to falling levels of oxygen, yet it is sensitive to increased level of carbon dioxide. The levels of oxygen in arterial blood vary little, even during exercise, but carbon dioxide levels vary in direct proportion to the level of physical activity. The more intense the exercise, the greater the carbon dioxide concentration in the blood. To combat this, your breathing rate increases to ensure the carbon dioxide can be expelled. Exercise results in an increase in the rate and depth of breathing. During exercise your muscles demand more oxygen and the corresponding increase in carbon dioxide production stimulates faster and deeper breathing. A little rise in breathing rate prior to exercise is known as an anticipatory rise. When exercise begins there is an immediate increase in breathing rate, this is when your receptors are working in both your muscles and your joints. The respiratory control centre is located in the brain. There are three receptors that send message to the control centre, they are called chemoreceptors, proprioceptors and thermoreceptors. Chemoreceptors detect increases in concentration of carbon dioxide. Proprioceptors inform the respiratory control centre of of the extent of movement taking place. Thermoreceptors detect an increase in body temperature that accompany exercise and cause breathing rate to increase. All these receptors send message to the respiratory control centre, diaphragm and intercostal muscles. After several minutes of aerobic exercise, breathing continues to rise, but as a slower rate, and it will level off if the exercise intensity remains constant. If you carry on exercising at a maximum level your breathing levels will rise to exhaustion. After exercise your rate returns to normal rapidly to begin then more slowly. During exercise, tidal volume increases to allow more air to pass through the lungs. The volume of air passing through the lungs each minute is known as the minute volume and is the product of breathing rate and the amount of air taken in with each breath. When we breathe in the external intercostals contract. However when we breathe out the external intercostals relax. The depth of breathing is increased by a greater expansion of the thoracic cavity. This is caused by the action of three muscles. The sternocleidmastiod raises the sternum and ribs upwards and outwards. Expiration is more active with intercostal muscles contracting to pull the rib cage inwards and downwards.