Blood pressure
Blood pressure is the pressure of the blood against the walls of the arteries which is caused from two forces. One is created by the heart as it pumps blood into the arteries and through the circulatory system, and the other is the force of the arteries as they resist the blood flow. A typical blood pressure reading is Diastolic 120/Systolic 80mmHg for the average adult male. Blood pressure varies with age, gender, physical activity levels and race for example people of Polynesian descent tend to have higher blood pressure naturally than Asian people. The two values correspond to the systolic value (the pressure when the heart contracts) and the diastolic value (the pressure when the heart relaxes between beats). The higher value is systolic and the lower value is systolic. Blood pressure is measured in milligrams of mercury, mmHg. A person with high blood pressure, for example 140/90mmHg is considered higher, increases their risk of heart disease or kidney failure because it increases the workload of the heart. A person’s blood pressure is determined by cardiac output and the resistance the blood has as it flows.
Resistance in blood flow is caused both by the size of the blood vessels through which it travels (smaller blood vessels the greater resistance) and by the thickness of the blood (thicker the blood the grater the resistance).
During exercise there is an increase in heart rate which will result in an increases cardiac output, as cardiac output increases with increases heart rate. Widening of the blood vessels feeding the working muscles acts to reduce blood pressure but this is counteracted by the increase in blood pressure caused by increased cardiac output. Exercise raises systolic pressure, but there is only a slight change in diastolic pressure. Straight after exercise there will be a fall in systolic pressure as the skeletal muscular pump is no longer pumping blood from the muscles to the heart. This can lead to blood pooling in the muscles which causes not enough blood going to the brain. This can lead to the athlete feeling nauseous or fainting.
P2
Respiratory system
The body unexpectedly insensitive to falling levels of oxygen required for exercise. But it is far more sensitive in increased levels of carbon dioxide. Oxygen gets rid of carbon dioxide in the body so this explains why oxygen is needed during exercise. The more intense the exercise the greater the concentration of carbon dioxide in the blood, to combat this your body increases its breathing rate to get more oxygen in and therefore making sure the carbon dioxide is excluded.
Breathing rate
Moderate to heavy exercise increases the amount of oxygen muscles use. For example, a trained athlete at rest might use about 250ml per minute, but may need as much as 3,600ml per minute during heavy exercise. While oxygen consumption is increasing, the amount of carbon dioxide produced increases also. Decreased blood oxygen and increased blood carbon dioxide levels quicken the respiratory centre therefore increasing breathing rate.
When exercise first begins, the initial response is an immediate and sharp increase in breathing rate. The increase in breathing rate during any exercise demands an increase in blood flow to the skeletal muscles. Therefore exercise increases demands on the respiratory and circulatory system. If either of these systems fails to meet the demands set by the body the athlete will feel out of breath. This is generally due to the heart not being able to move enough blood the muscles and lungs, and not the inability of the respiratory system to provide enough oxygen.
Intercostal muscles
During the breathing process, the intercostal muscles contract, causing the ribs and the sternum to move upwards and outwards. While this process takes place, the diaphragm muscles contract, causing the diaphragm to move down so the diaphragm can effectively flatten. The combined movements of the ribs, sternum and diaphragm cause the lungs to increase in volume, while the air pressure within the lungs decreases s below the outside air pressure. The result is that the outside air pressure forces air from the outside environment into the lungs.
During exercise forced breathing is used. This differs from normal breathing because the internal intercostals muscles contract, moving the ribs and sternum up and outwards more forcibly. In exercise and performance, the strength and efficiency of the intecostal muscles are increased because of the work they have to do.
Tidal volume
Tidal volume is the volume of air inhaled and exhaled in one breath. Exercise results in an increase in tidal volume over 1 minute (minute ventilation). This rise is due to the working muscles and joints making minute ventilation increase. After exercise tidal volume and the frequency of breath returns to normal.
Valsalva manoeuvre
The valsalva manoeuvre is performed by forcibly exhaling with the mouth closed and nose pinched, forcing air into the middle ear. The manoeuvre can be used to test cardiac function.
The body normally reacts in four phases to this:
∙ Pressure rises in the chest and forces blood out, which causes a rise in blood pressure.
∙ Return of blood to the heart is hindered by the pressure inside the chest. The output of the heart is reduced and blood pressure falls. During this time the pulse rate rises.
∙ The pressure on the chest is released allowing the heart to function normally again, so cardiac output starts to increases.
∙ Blood returning to the heart is enhanced by the return of the blood that has been held back, causing a rapid rise in cardiac output and blood pressure.
Pulmonary ventilation
Pulmonary ventilation is commonly referred to as breathing. It is the process of air flowing into the lungs during inhalation and out of the lungs during exhalation. Air flows because of the pressure differences between the atmosphere and the gases inside the lungs. Muscular breathing movements and recoil of elastic tissues create the changes in pressure that result in ventilation. Pulmonary ventilation involves 3 pressures:
∙ Atmospheric pressure- the pressure of the air outside the body.
∙ Intra alveolar pressure- the pressure inside the alveoli of the lungs.
∙ Intrapleural pressure- the pressure within the pleural cavity.
During exercise, the breathing rate of an athlete increases. The respiratory centre sends impulses to the internal intercostal muscles to speed up the breathing process.
Neuromuscular system
Neuromuscular refers to both the nervous system and muscular systems. There are two types of nerves:
∙ Sensory nerves which carry information from the skin to the central nervous system.
∙ Motor nerves that carry information from our central nervous system to our muscles.
Nervous control of muscular contraction
Nerves stimulate muscles to contract. There are three basic types of contraction each with different contraction patterns. All of these contractions occur to some extent during exercise.
∙ Isotonic contraction: muscle shortens as it develops tension. It is the most familiar type of contraction, the kind used in lifting or curling exercises.
∙ Isometric contraction: the muscle develops tension but does not change its length. Holding the plank position is a good example of this.
∙ Isokinetic contraction: the muscle contracts to its maximum at a constant speed over the full range of movement. An example would be the arm stroke used in the front crawl stroke.
Neuromuscular junction
Neuromuscular junctions connect the end of a myelinated motor neurone to a muscular fibre, to which it transmits nerve impulses. When an impulse reaches the end of the neurone side of the junction, it causes the release of acetylcholine (Ach) which is the primary neurotransmitter. This causes the release of calcium ions, this initiates muscle contraction of myosin heads to the calcium released from troponin (actin).
(fig4)
Motor unit
Muscle fibers are connected by neurons that are located in the spinal cord. The nerve fibers of these motor neurons leave the spinal cord and are distributed to the motor nerves. Each motor axon branches several times and connects to many muscle fibers. The combination of a single motor neuron and all the muscle fibers it innervates is called a motor unit. Although the muscle fibers of a given motor unit tend to be located near one another, motor units have overlapping areas. To sustain muscle contraction, the motor units must be repeatedly activated (John V Basmajian). As the firing rates of motor units active in a contraction increase, the twitches connected with each firing will eventually combine to produce large forces.
(fig 3)
Muscle spindles
A muscle spindle is a sensory receptor, which is an organ placed within the muscle which primarily detects the changes in length, or the stretch of the muscles. They convey the message of the changes in length and the extent that the muscle is being stretched through the central nervous system the via sensory neurones . The purpose is to detect when the muscle is in a state of contraction. When a muscle is contracted it changes the tension of the muscle spindle. This is relayed to the central nervous system that deals with the information by either increasing the contraction of the muscle or relaxing the muscle.
Energy systems
The body takes in chemical energy in forms of food. This is stored in the body in the form of adenosine triphosphate (ATP), a high energy compound that is converted into kinetic energy and used to create movement. The movement of muscles requires ATP, so it follows that the ability of an athlete to move his or her muscles requires ATP.
(fig2)
ATP
The body only stores a small amount of ATP in cells, only enough to power a few seconds (1-4) of all out exercise. Therefore the body must replace ATP on a continual basis. ATP consists of a base (adenine) and three phosphate groups. It is formed by a reaction between an adenosine diphosphate (ADP) molecule and a phosphate. When a molecule of ATP is combined with water, the last phosphate group splits off and energy is released.
Creatine phosphate system
ATP and creatine phosphate (or PCr) make up the ATP-PCr system. PCr is broken down releasing a phosphate and energy, which is then used to rebuild ATP.
The ATP-PCr system can operate with or without oxygen, and is said to be anaerobic. During the first five seconds of exercise the ATP-CPr system is relied on. ATP lasts only a few seconds, then PCr buffering the drop in ATP for another 5-8 seconds or so. The ATP-PCr system can sustain all out exercise for 3-15 seconds and during this time power output is at its greatest, so it would be used in weightlifting.
Lactic acid system
Glycolysis is the breakdown of glucose and is made up of a series of enzymatic reactions. The carbohydrates we eat supply the body with glucose, which can be stored as glycogen in the muscles and liver. The end product of gycolysis is pyruvic acid. The lactic acid system kicks in after ATP-PCr system and last roughly between 55-90 seconds. It is used in high intensity exercise such as a 400m race.
Anaerobic glycolysis
Anaerobic glycolysis is the process by which the normal pathway of glycolysis is routed to produce lactic acid. It happens at times when energy is required in the absence of qxygen. It is vital for tissues with high energy needs, insufficient oxygen supply or in the absence of oxidative enzymes.
Bibliography
(fig1)- 28/10/09
(fig2)- 1/11/09
(fig3)- 15/12/09
(fig4)- 15/12/09
