Lect 9. Physiological Response During Incremental Exercise PDF

Exercise physiology Physiological response during incremental exercise of increasing intensity DR. Nivin Sharawy Professor of Clinical Physiology User name: [email protected]  Metabolic changes during 01 exercise...

Exercise physiology Physiological response during incremental exercise of increasing intensity DR. Nivin Sharawy Professor of Clinical Physiology User name: [email protected]  Metabolic changes during 01 exercise 02 Cardiac and respiratory changes during exercise Endocrine changes during Exercise 03 04 Regulatory & structural changes with exercise Metabolic response: As the intensity of exercise increases, oxygen uptake (VO2) also increases until it reaches a maximum or plateau. This point is called maximum oxygen uptake (VO2 max.), and it denotes the point at which an individual cannot increase his oxygen consumption anymore. To increase oxygen consumption during exercise the respiratory system must provide more oxygen, the cardiac system must distribute more blood to the active muscles and lastly the muscle metabolic systems must utilize this increased oxygen provided. Respiratory response Extra amounts of oxygen are provided to the blood during exercise through  Ventilation increases linearly with respect to oxygen uptake (VO2). The increase in ventilation is caused initially by an increase in both tidal volume and respiratory rate. However, as exercise increases tidal volume reaches a plateau and the increase is then only due to increasing respiratory rate. Respiratory response Extra amounts of oxygen are provided to the blood during exercise through  Three-fold increase in oxygen diffusing capacity  Due to perfusion of all pulmonary capillaries, thus providing a greater surface area for oxygen diffusion Arterial - venous oxygen content difference (A-V) O2. The (A-V) O2 difference is the difference between the oxygen content of the arterial and venous blood. It is widened during exercise allowing more oxygen delivery to the tissues due to:  Changes in distribution of blood flow leading to greater flow to the actively exercising muscles where oxygen extraction is high.  Local muscle extraction is high due to changes which lead to shift the oxygen dissociation curve to right allowing more delivery of oxygen. Cardiac response Cardiac output (CO) increases during exercise to pump more blood to the exercising muscles. The heart rate increases linearly with oxygen uptake, while stroke volume increases early during exercise from about 70ml/beat to a maximum of about 110 ml/beat where it plateaus. Thereafter, the increase in CO depends on the increase in heart rate. The maximum heart rate allowed is 220 - age. Endocrinal response during exercise Exercise increases the blood levels of: Growth hormone Thyroxine Aldosterone Physiological adaptations to regular physical training A. Regulatory response: rapid, develops within few weeks of training.  A shift from sympathetic to parasympathetic activity.  A redistribution of blood flow.  Initiation of sweating at a lower core temperature.  Increased sensitivity and/or responsiveness to insulin allowing an improved glucose tolerance at lower insulin levels.  Physiological adaptations to regular physical training B. Structural response: slow, continues for months or years. It includes, an increased muscle mass, cardiac tissue and bone with parallel increase in capillary blood supply. Metabolic and cellular adaptations:  Increased maximum oxygen consumption.  Increased anaerobic power by increasing the activity of the enzymes of glycolysis.  Increased aerobic power through increasing myoglobin levels in active muscles, increasing the activity of kreb's cycle & mitochondrial respiratory chain enzymes and changing fuel usage, increasing fat utilization thus sparing glycogen and glucose for anaerobic activity.  Muscle fiber changes: mainly hypertrophy with increased myofibrils, number and size of mitochondria, stored ATP, CP, glycogen and triglyceride levels  Physiological adaptations to regular physical training B. Structural response: slow, continues for months or years. Respiratory adaptation:  The adaptation of a slower and deeper pattern of breathing. Cardiac adaptation:  The heart of an athlete is larger that that of a normal person.  The stimulus for cardiac hypertrophy seems to be due to high preload to the ventricles for a long time.  Cardiac hypertrophy is associated with an Increase in cross-section of the major coronary arteries, an increase in capillary density and an increase in myocardial perfusion. Physiological adaptations to regular physical training With training, the increase in CO during exercise depends more on the increase in stroke volume rather than on heart rate. The cardiac output is increased. This is achieved by a large stroke volume at a reduced heart rate. Thus, the heart pumping effect is 40-50% greater in athletes. The decrease in heart rate in, athletes is mainly due to altered autonomic activity with decrease of both catecholamine output and sensitivity  Effect of drugs on exercise performance Caffeine:  Small amounts of caffeine were recorded to increase exercise performance. Male sex hormones: (androgens):  Undoubtedly androgens can increase muscle strength, however they cause liver damage and liver cancer.  Also, in men it leads to decreased testicular functions it causes hirsutism and cessation of menses in women. Cocaine:  Experiments have failed to prove any value of these drugs in exercise performance except as a psychic stimulant. Interaction of these drugs with catecholamines released during exercise might cause death mainly due to over excitability of the heart leading to ventricular fibrillation. Key Points Alterations in metabolism, heart and respiration during exercise Physiological adaptations during exercise (regulatory and structural)