Exercise physiology Lecture (1) Prof. Dr. Ibrahim M. Zoheiry Assistant Professor Of Physical Therapy Acting Chariman Of Basic Science Department Faculty Of Phsyical Therapy October 6 University Definition of Exercise physiology • Is the study of the effects of exercise on the body concerned with the body’s responses & adaptations to the stress of exercise, ranging from the system level(cardiovascular system) to the subcellular level (production of ATP for energy). Importance of exercise 1- to design effective fitness programs for people of all ages. 2- to guide the development & implementations of cardiac rehabilitation programs, 3-to plan programs to help children & youths to incorporate physical activity into their life 4- to structure rehabilitation programs for injured athletes. Energy • All plants & animals depend on energy to sustain life, Humans derive this energy from food. • All energy forms are interchangeable chemical electrical electromagnetic Nuclear mechanical thermal 60-70% Heat Energy for Cellular Activity • Human cells can break down these 3 basic food components to release the stored energy. • Energy is stored in food in the form of carbohydrate, fats & proteins. • Humans obtain energy by eating plants, or animals that feed on plants. • Chemical reactions in plants convert light into stored chemical energy. • All energy originates from the sun as light energy. Energy sources FOOD Carbon Hydrogen Nitrogen Oxygen •Food is NOT used directly for cellular activity because molecular bonds in foods are weak & provide little energy when broken. •Energy in food molecules’ stored in the form of a high-energy compound called adenosine triphosphate (ATP). Energy sources • At rest, energy that body needs is derived almost equally from the breakdown of CHO & fats. • Proteins provide little energy for cellular function/activity During mild to severe exercise, more CHO is used. • In maximal, short-duration exercise, CHO is used exclusively to produce ATP. Carbohydrates (CHO) • CHO glucose Via blood all body tissues. • • Glycogen (Stored in cytoplasm until the cell use it to form ATP ). • Liver & muscle glycogen reserves are limited (‹ 2000 Kcal) unless CHO is increased. Fats • Fat provides 2 times more energy than CHO but less accessible for cellular • metabolism because it must first be reduced from its complex form (triglyceride) to its basic components: glycerol & free fatty acids (FFA). • Only FFA are used to form ATP. • Fat is a good source of energy, can be stored exceeding 70,000 kcal of energy. Proteins • Protein can be used as energy source if convert into glucose. • Protein converted into glucose through gluconeogenesis. • In severe energy depletion (starvation), protein can be converted to FFA for cellular energy through lipogenesis. • Protein can supply up to 5-10% of the energy needed to sustain prolonged exercise. • Protein can be used as energy source in basic form of amino acids. Energy yield • 1 g of CHO (C6H12O6) yields 4 kcal of energy. • 1 g of fat (C16H18O2) yields 9 kcal of energy. • 1 g of protein (NH2 + CO2H) yields 4.1 kcal of energy. • (Though 1 g of fat can generate 2.25 times as much as a similar amount of CHO, it also takes substantially more oxygen to metabolize fat than CHO) Bioenergetics • The chemical processes involved with the production of cellular ATP by converting foodstuffs (i.e., carbohydrates, fats, proteins) into a biologically usable form of energy. ATP Production • ATP ATPase phosphorylation . Aerobic metabolism = Oxidative phosphorylation ADP +Pi Anaerobic metabolism = ATP-PC system ATP-PC system (Anaerobic ATP production ) • The simplest of the energy system. • PC • Creatine Kinase Pi + C + energy (1 mole) ADP + Pi + energy 1 ATP • Functions: 1- Provides energy for short-term and high-intensity exercise that lasting about 3-15 seconds. 2- Maintain ATP levels N.B : Not used directly to accomplish cellular work. Glycolytic system If O2 is not available to accept the hydrogen ions in the mitochondria, pyruvic acid can accept the hydrogen ions to form the lactic acid. Hazards of Lactic acid 1. The accumulation of lactic acid is a major limitation of anaerobic glycolysis. 2. Impairs glycolytic enzymes functions 3. Decreases the fibers calcium binding capacity >>> Impede muscle contraction Oxidative system ( Aerobic process) • The body’s most complex energy system, which generates energy by breakdown of fuels with the aid of O2 (cellular respiration). • Has a very high-energy yield and yields more energy than the ATP-PC or glycolytic system. • Main energy production during endurance activities. • Oxidative production of ATP occurs within the mitochondria Oxidative production of ATP 1. Oxidation of CHO: a. Aerobic glycolysis b. The Krebs cycle c. The electron transport chain 2. Oxidation of Fat a. ß Oxidation b. Krebs cycle c. The electron transport chain Oxidation of CHO 1. Aerobic glycolysis • In CHO metabolism, glucose or glycogen is broken down to pyruvic acid via glycolytic enzymes. • Hydrogen is released as glucose is metabolized to pyruvic acid. • In the presence of O2, the pyruvic acid is converted into acetyl coenzyme A (acetyl CoA) of ATP. • 1 mole of glucose produces 2 moles of ATP or 1 mole of glycogen produces 3 moles Oxidation of CHO 2. Krebs cycle Oxidation of CHO 2. Krebs cycle • If 1 mole of glucose, the net gain is 38 ATP (1 mole of ATP is used for 1 mole of glycogen generates up to 39 moles of ATP. • Energy yield from Carbohydrate conversion to glucose-6-phosphate before glycolysis). Oxidation of Fats • Muscle & liver glycogen stores provide only 1,200 2,000 kcal of energy. • Fat stored inside the muscle fibers (fat cells) can supply about 70,000 - 75,000 kcal. • Triglycerides (major energy sources) stored in fat cells in the skeletal muscle fibers. • Triglycerides break down to its basic units to be used for energy: 1 mol of glycerol to 3 moles of free fatty acids/FFA (= process lipolysis with lipases enzymes). • FFA can enter blood & be transported throughout the body, entering muscle fibers by diffusion. Oxidation of Fats 1. ß Oxidation • FFA Catabolism ß Oxidation 8 moles of acetic acid 8 moles of acetyl CoA. • ( Each acetic acid converted to acetyl CoA ). • • Acetyl CoA enters the krebs cycle as free fatty acids have more carbon so more energy is produced , for example : Palmitic acid ( 16carbon FFA produce 129 molecules of ATP . Protein metabolism • Proteins (amino acids) are also used as body fuels. • Some amino acids can be converted into glucose (gluconeogenesis) • Some can be converted into various intermediates of oxidative metabolism (such aspyruvate or acetyl CoA) to enter the oxidative process. • Protein’s energy yield is not easy because it contains nitrogen (N). Protein metabolism • When amino acids are catabolized, some of the released N is used to form new amino acids, but remaining N cannot be oxidized by body. • N is converted into urea & then excreted in the urine. This conversion use ATP, so some energy is spent in this process. • In laboratory, 1 gram of protein = 5.65 kcal of energy. Protein metabolism • When metabolized in the body, energy used to convert N to urea, energy yield is only about 5.20 kcal per gram (8% less than the lab. Value). • Healthy body utilizes little protein during rest & exercise (< 5-10% of total energy expended). • Estimates of energy expenditure generally ignore protein metabolism. Oxidative capacity of muscle ( QO2) • Oxidative capacity (QO ) - A measure of the 2 muscle’s maximal capacity to use oxygen. • Oxidative capacity depends on: a. Enzyme Activity b. Fiber-type Composition c. Oxygen Needs Oxidative capacity of muscle ( QO2) • A- Enzyme activity : • Many enzymes are required for oxidation. • The enzyme activity of the muscle fibers provides an indication of the oxidative potential. • The enzymes most frequently measured are SDH (succinate dehydrogenase), CS (citrate synthase) & mitochondria enzymes in the Krebs cycle. • Endurance athletes’ muscles have oxidative enzyme activities 2-4 times greater than those untrained men & women. Oxidative capacity of muscle ( QO2) • B- Fiber type composition: Oxidative capacity of muscle ( QO2) Oxygen needs • Oxidative metabolism depends on an adequate supply of O2. • When at rest, body’s need for ATP is small, requiring minimal O2 delivery. • As exercise intensity increases, to meet the energy demands, the rate of oxidative ATP production also increases. • In an effort to satisfy the muscle need for O2: 1. rate & depth of the respiration increase 2. improving gas exchange in the lungs 3. heart beats faster 4. pumping more oxygenated blood to the muscle. Fatigue • a feeling of lack of energy and motivation that can be physical, mental or both. Causes of fatigue 1. Depletion of PC or glycogen. • will impairs ATP production, thus fatigue is caused by inadequate energy supply. 2. Accumulation of metabolic by-products. • E.g : Accumulation of hydrogen (H+) : Decrease muscle PH Muscle acidification ( acidosis ) Inhibits the action of glycolytic enzyme slowing the rate of glycolysis & ATP production Inhibit muscle contraction Causes of fatigue 3. Failure of neural transmission in the muscle fiber. • Fatigue may occur at the motor end plate, preventing nerves impulse transmission to the muscle fiber membrane, thus cause the neuromuscular block and leads to neuromuscular fatigue. 4. CNS may cause fatigue. Psychologically exhausted/fatigue Inhibit the athlete’s willingness to tolerate further pain or to continue exercise.
