Physiological Adaptations in Response to Training Examine the relationship between the principles of training, physiological adaptations and improved performance.

In response to training the body makes adaptations or adjustments to the level of stress imposed on it. These adaptations allow the body to function more comfortably at existing levels of stress and respond more efficiently to new levels of stress. Although progressive improvements can be seen throughout a training program, it usually takes around 12 weeks to realise the entire benefits. Training will cause adaptation to a number of capacities including, resting heart rate, stroke volume, cardiac output, oxygen uptake, lung capacity, haemoglobin level, muscle hypertrophy and effect slow and fast twitch muscle fibres.

Resting Heart Rate Aerobic training causes a lowering of the resting heart rate. This is because of the improved efficiency of the cardiovascular system. An untrained resting heart rate is usually between 70 and 90 beats per minute. Trained athletes can have a resting heart rate as low as 30 beats per minute.

Stroke Volume Stroke volume increases as a result of aerobic training. It refers to the amount of blood ejected by the left ventricle of the heart during a contraction. It is measured in mL/beat. Untrained people may have a stroke volume of 70-80ml, while people involved in aerobic training may have a stroke volume of 90- 125ml. This occurs because a trained athlete has a stronger heart muscle, capable of a more forceful contraction and an increase in the capacity of the left ventricle, enabling more blood to be pumped out in each contraction.

Cardiac Output Cardiac output is the amount of blood pumped by the heart per a minute. It is determined by multiplying heart rate and stroke volume. The cardiac output of a trained athlete may be similar to an untrained person at rest, but during exercise the cardiac output of the trained athlete will be greater. An untrained person may have a cardiac output of 15 to 20 litres per a minute while a trained person may have 20 to 25 litres per a minute. In highly trained endurance athletes, cardiac output may even rise as high as 40 litres per a minute.

Oxygen Uptake Oxygen uptake (VO2) is the amount of oxygen that is consumed by the mitochondria in the cells in order to produce aerobic energy. Maximal oxygen uptake (VO2max) is the maximum amount of oxygen that the body can take in and utilise for production of aerobic energy. It is used to measure cardiorespiratory fitness. A person’s VO2max is determined by factors such as: Heredity Age - VO2max increases until the mid twenties and declines thereafter. Gender - males generally have higher VO2max levels due to increased muscle percentages and haemoglobin levels. Training Status - VO2max increases in response to aerobic training.

Lung Capacity Lung capacity is the total amount of oxygen that an individual’s lungs can hold. Lung capacity remains relatively unchanged with most training programs, but may improve slightly with maximal training. Training can improve a person’s vital capacity i.e. the amount of air that can be breathed in and out during a single breath. Vital capacity is different to lung capacity due to the fact that there is always air left in the lungs, even after the most forceful expiration. This leftover air is called residual volume. The total lung capacity is about 6000mL in males and slightly less in females due to their smaller size.

Haemoglobin Level Haemoglobin is found in red blood cells. Each red blood cell contains 250 million haemoglobin molecules. He average male has 14.3 grams of haemoglobin per 100mL of blood, while the average female has 13.9 grams per 100mL of blood. Women's lower haemoglobin levels contribute to lower VO2 max values. Haemoglobin is essential as it binds to oxygen, enabling transportation via the circulatory system as oxygen does not dissolve easily in fluids of the body, if haemoglobin was not present in the body we would require 80 litres of blood to transport enough oxygen to live. Haemoglobin levels can improve by up to 20% as a result of aerobic training.

Muscle Hypertrophy This term defines the process of muscle enlargement and strength gains in response to resistance training. Training does not increase the number of muscle fibres, rather the size of the fibres. While length of muscles remains the unchanged, the size of the muscle becomes larger as an increase in its mass and cross-sectional area. Hypertrophy is induced by training programs that stimulate activity in muscle fibres causing them to grow. Without stimulation, muscle fibres can reduce in size, a condition known as muscular atrophy.

Effect on Fast and Slow Twitch Muscle Fibres……FYI…. Slow twitch muscle fibres or type 1 fibres which are red in colour contract slowly and for long periods of time. The are recruited for endurance-type activities such as marathons. Fast twitch muscle fibres or type 2 fibres are white in colour and reach peak tension quickly and are recruited for power and explosive movements such as throwing, sprinting and lifting. Most people have approximately even numbers of slow and fast twitch muscle fibres, however some individuals genetically have higher proportions of one type or the other. Physiological adaptation occur to this type of muscle fibre when they are subjected to training that is specific to their role.

Effect on Fast and Slow Twitch Muscle Fibres cont. FYI…….. Aerobic training causes the following adaptations to occur in slow twitch fibres: Hypertrophy of slow twitch muscle fibres. Capillary growth of up to an increase of 15% surrounding muscle fibres to increase gaseous exchange and the removal of waste products. Mitochondrial function. An increase in the number of mitochondria cells as well as an increase in their size and efficiency in utilising oxygen to produce ATP. Myoglobin content. Myoglobin is responsible for transporting oxygen from the cell membrane to the mitochondria and storing it for use when necessary. Endurance training can increase myoglobin content by up to 80%. Oxidative enzymes. Increase in levels of activity making the production of energy more efficient.

Effect on Fast and Slow Twitch Muscle Fibres cont. FYI…… Anaerobic training causes the following adaptations to occur in fast twitch fibres: ATP/PC supply. Fuel supply and the efficiency with which fuel is used increases. Glycolytic enzymes. These increase, improving the functioning within cells. Hypertrophy. This has the potential to increase considerably and is dependant on the type, frequency and intensity of training. Lactic acid tolerance. Training increases the ability of fast twitch fibres to tolerate lactic acid, allowing anaerobic performance to be sustained for longer periods of time.