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Fitness can be Endurance Flexibility Strength Speed What happens when the muscle contracts. The skeletal frame is covered with approximately 600 muscles, which represent about 40% of the body’s weight. A muscle is a collection of long fibres made up of cells and grouped in bundles. Each bundle is separately wrapped in a sheath that holds it together. This is further sub-divided into actin and myosin filaments. Stimulation of a muscle Muscles work like engines by burning fuel to produce movement. They are energy converters, changing the chemical energy in the food we eat into the energy of movement (kinetic energy). When the brain stimulates a muscle to contract, a ready source of energy is required to provide the fuel necessary to perform the contraction. Types of muscle There are two distinct mixture of fibres, which are two distinct types: fast-twitch which is the quick sprint type and the longer running cruising type for long distance known as the slow-twitch fibre. A fast-twitch muscle fibre is like the engine of a sprint-type racing car. It can produce high speed movement for short periods of time. Fast-twitch (Anaerobic) The fast twitch needs a premium fuel (carbohydrate) and produces a large amount of waste- lactic acid because it doesn’t burn up completely. The high level of lactic acid, together with the limited supply of fuel, means that a sportsperson can never use these fast twitch fibres for very long. Build up of lactic will impair action. Slow-twitch (Aerobic) The slow-twitch muscle fibre is like the engine of a touring car. It produces less power, which means less speed; but it can run for much longer periods at this cruising speed. It gets by on a lower grade fuel, a mixture of fat and carbohydrate. The fuel is more completely burned and the Co2 is easier to handle. Cardiovascular Fitness The contraction of muscle requires energy and in a race the athletes will use up quite an amount of energy. The energy comes from the oxidation of foodstuffs. Digested foodstuffs combine with o2 to produce co2 and water and energy is released. Vigorous Physical Activity Energy becomes available to the muscles if foodstuffs and o2 are supplied to it. In the course of vigorous activity like a race o2 has to be taken to the muscles while the activity is in progress. Bronchus The bronchi are the tubes which carry air from the trachea to the inner recesses of the lungs where it can transfer oxygen to the blood in small air sacs called alveoli Oxygen-food –energyco2 water Oxygen is taken to the muscles by the cardiorespiratory system. It is responsible for supplying oxygen to the blood and expelling waste gases of which Co2 is a major constituent. Blood How the blood carries o2 O2 is carried in the blood stream by the Haemoglobin in the red blood cells Blood contains 44% red blood cells. Erthrocytes This may be reduced by disease or the lack of iron in the diet, which means that not as much 02 can be transported around the body. 50% red blood cells: E.P.O. (Erythropoietin Interior of the Heart It is the efficiency of the heart which determines the performance of an athlete in an event lasting longer than a few seconds. Trained athletes tend to have larger hearts. How athletes and non athletes differ The size of the heart in the athlete is larger. Trained athletes tend to have a greater number of red blood cells. The athlete tends to have a greater stroke volume than the non athlete. Trained athletes tend to have a resting heart rate of 40-50 beats per minute. Untrained athletes tend to have a resting heart rate of 70-80 beats per minute. More enzymes present in an athlete. Measuring Cardiovascular Fitness The cardiovascular fitness of an athlete can be assessed by measuring how much 02 an athlete can pump round his body in one minute. This is known as the Maximum oxygen intake or V02 max. V02 max of various athletes Cross country skiers: 6 litres of o2 per minute. 1500 Metre runners: 5 litres per minute. Untrained subjects have values of 3 litres per minute.