Introduction to Kinesiology: Energy Systems and Muscle Fiber Types

Consider… “How are nutrients in food resynthesized into a universal form of energy to fuel our bodies’ physiological processes?” “Which of the body’s energy systems is more important in short-term and medium-term, high-intensity activities?”

What are Nutrients? Nutrients are chemical substances obtained from food and used by the body for many different processes. They are the raw materials our bodies need to supply energy, to regulate cellular activities, and to build and repair tissues. All organisms—including humans—require nutrients to perform their life functions and to obtain the energy necessary

The Three Energy Nutrients The food we take in contains three key energy nutrients that are broken down over the course of digestion: Carbohydrates- most important Proteins Fats © iStockphoto.com/”Roman Chmiel” © iStockphoto.com/”og-vision/OlgaLIS” © iStockphoto.com/”Kativ”

CARBOHYDRATES Yield: 4.1 kilocalories per gram Are plentiful throughout the body and are easily accessible Get almost entirely from foods that originate from plants, such as vegetables, fruits, and grain-based foods, such as breads and pasta. CHO’s are stored in skeletal muscles as glucose and in the liver as glycogen.

FATS Provide 9.3 kilo calories /gram The primary types of fat found in muscle cells and adipose tissue are converted for use as energy and are known as fatty acids-Fatty acids are stored in the muscles/body as triglycerides Through lipolysis, fatty acids are broken down and become an energy source Fatty acids enter the energy system during Krebs Cycle Need to be converted to aceytl-CoA through beta-oxidation – occurs within the mitochondria of cells and involves four chemical reactions, yielding acetyl-CoA. Acetyl-CoA enters the Krebs cycle and becomes a primary energy source for the production of ATP within the electron transport chain.

PROTEINS Provide 4.3 calories per gram No reserves in the body – are part of body tissue and are actively engaged as components of the metabolic system Protein in the body is comprised of amino acids-which are used by the body to form various tissues. Must be broken into amino acids, then converted to glycogen, then transported as glucose to the muscles through blood Best for endurance activities and in more chronic conditions when glycogen reserves are significantly diminished. PROTEINS

Approximate Energy Sources for different sport activities

ENERGY ATP  ADP + P +ENERGY . . .but why is it important that we ingest carbohydrates? ENERGY -The final form this free energy takes is adenosine triphosphate (ATP), the common energy molecule for all living things. -ATP captures the chemical energy resulting from the breakdown of food and can be used to fuel the various cellular processes. -To be usable, these nutrients need to be reconstituted into a universal form of energy- “free energy”- which can then be used for muscle contraction and many other physiological processes. ATP (Adenosine Triphosphate) Youtube What ATP is and How it Works - 3 phosphates attached to adenosine ATP  ADP + P +ENERGY Energy is released when a trailing phosphate atom is broken from the ATP molecule – resulting in ADP Energy

Energy Systems 1. Anaerobic System 2. Aerobic System The question we will be answering is not how the body uses ATP, but rather how the body goes about resynthesizing ATP. Energy Systems 2 methods for resynthesizing ATP 1. Anaerobic System -without oxygen -occurs in the muscle fibre -quick, powerful short activities These systems work together, coexist and overlap All physical activity relies on some combination of these systems 2. Aerobic System -with oxygen -occurs in the mitochondria -several complex reactions- leads to the complete breakdown of glucose- fat and protein also enter the cycle at this time. -endurance activities

ATP-PC System (anaerobic alactic) Three Metabolic Pathways: Within the two energy systems there are three main metabolic pathways by which ATP energy reserves are restored. ATP-PC System (anaerobic alactic) Glycolysis (anaerobic lactic) Cellular respiration (aerobic)

3 PATHWAYS ATP-PC Anaerobic alactic no oxygen, no lactic acid Glycolysis Anaerobic Lactic no oxygen, lactic acid as by-product Cellular Respiration a.k.a. (Oxidative Phosphorylation) Aerobic uses oxygen

for every PC until PC is depleted 1. ATP-PC System Anaerobic alactic Without O2 No lactic acid First and simplest of the 2 anaerobic pathways Short, powerful energy bursts  10-15 seconds of work PC + ADP  ATP + Creatine 1 ATP molecule produced for every PC until PC is depleted Phosphocreatine -High energy molecule- where phosphate can be broken off easily and used to convert ADP back to ATP -Small stores found in muscles and readily accessible - Highest rate of ATP synthesis -Sprinting, high jump, powerlifting

Muscles do not have large stores of phosphocreatine, after 10-15 seconds, when the ATP produced by this method is depleted, the athlete needs to rely increasingly on a second system to re-synthesize still more ATP in order to satisfy the energy demand. The full replenishment of phosphocreatine itself requires ATP and occurs during the recovery period. Occurs rapidly and as a result of supplies of ATP being created during the aerobic processes. This ATP is utilized to recombine phosphate and creatine, and takes 2-5 minutes

Questions & Exercise Workbook Pg.128 Exercise 7.2 Complete Table for ATP-PC Answer the Following Questions: Describe the role of fats, proteins, and carbohydrates in the production of ATP. 2. What are the three metabolic pathways to create sufficient energy?

2. Glycolysis Anaerobic lactic Produces lactic acid Plentiful in the human body, partial breakdown of glucose in cytoplasm- no oxygen needed with lactic acid as a by-product ATP energy produced during this process will allow an athlete to engage in a high level of performance for an additional 1-3 minutes- 15 seconds to 3 minutes. -Since glucose is normally plentiful throughout the body, glycolysis is an ideal backup to the ATP-PC system for medium-to term physical activities i.e.. 400-800m or a shift in hockey. Glycolysis thought of as the first sequence of reactions in the metabolism of glucose- here glucose is partially broken down to provide usable energy in the form of ATP

C6H12O6 + 2ADP + 2Pi  2C3H6O3 + 2ATP + 2H2O Although ATP production is rapid, glycolysis is a much more complex process 11 separate biochemical reactions Yields twice as much ATP as the ATP-PC system C6H12O6 + 2ADP + 2Pi  2C3H6O3 + 2ATP + 2H2O Pyruvate Glucose -main product of glycolysis is pyruvate- under aerobic conditions when O2 is readily available to muscle pyruvate is the start of the 3rd (aerobic) system eventually leading to the breakdown of glucose and large quantities of ATP In the absence of O2 the process is halted at the glycolysis stage as lactic acid hampers further activitiy Pyruvic acid is converted to lactic acid and exhaustion or painful muscle agony beings to set in. Need 30-60 min of exercise recovery or 1-2 hours of rest recovery Total ATP count = 2 two molecules of ATP for every molecule of glucose

Exercise Workbook Pg.128 Exercise 7.2 Complete Table for Glycolysis

© 2015 Thompson Educational Publishing, Inc. Cellular Respiration Cellular respiration refers to the process in which the body’s cells use oxygen to generate energy through the various metabolic pathways found in the mitochondria of cells. In the presence of oxygen, cellular respiration can, in theory, sustain activity for a very long time, or until other physiological limits are reached. This is the pathway that underlies endurance-type events (eg., a marathon run). © 2015 Thompson Educational Publishing, Inc.

Cellular Respiration Aerobic- yields large amounts of ATP When sufficient O2 is present, the pyruvate left over from Glycolysis will move into a new, even more complex pathway. . . Aerobic- yields large amounts of ATP Cellular Respiration -involves oxygen and the complete breakdown of glucose in the mitochondria of cells -it kicks in roughly 90 sec into activity and lasts for endurance activities -fats and proteins also used as energy sources in this pathway As a last resort Exercise longer than 20 minutes -involves 3 separate pathways:

Glycolysis: The First Sub- Pathway of Cellular Respiration This first stage or sub-pathway is the same as in the aerobic lactic system except that, in the presence of oxygen, pyruvic acid is converted to acetyl CoA rather than lactic acid. Acetyl CoA then enters a more complicated pathway known as the Krebs cycle (or “citric acid cycle”). © 2015 Thompson Educational Publishing, Inc.

The Krebs Cycle: The Second Sub- Pathway of Cellular Respiration The Krebs cycle involves a complex series of eight chemical reactions. (Hans Adolf Krebs first described this process in 1937—for which he was awarded a Nobel Prize in 1953.) Two ATP molecules are produced at the end of this process, along with new compounds capable of storing “high-energy” electrons. These high-energy electrons are then sent to a process within the mitochondria of cells, known as the electron transport chain. © 2015 Thompson Educational Publishing, Inc. 40

© 2015 Thompson Educational Publishing, Inc. The Electron Transport Chain: The Third Sub-Pathway of Cellular Respiration During the third and final sequence of reactions, known as the electronic transport chain, large amounts of ATP energy are produced (in total, 36 molecules). Carbon dioxide and water are the only by- products. The “chain” is a series of electron carriers and protein complexes that accept and donate electrons in a sequential series. The final electron acceptor is oxygen. © 2015 Thompson Educational Publishing, Inc.

The Kreb’s Cycle

Electron Transport Chain The third and most “profitable” sub-pathway is the final stage of cellular respiration Electron Transport Chain -occuring in the mitochondria, the ETC takes high energy electrons, found within FADH and NADH molecules, through a chainlike process -this process creates VAST amounts of ATP with only CO2 and water as by products

C6H12O6 + 6O2 + 36ADP + 36Pi  6 CO2 + 36ATP + 6H2O The electron transport chain contributes a whopping 32 ATP to the cellular respiration process C6H12O6 + 6O2 + 36ADP + 36Pi  6 CO2 + 36ATP + 6H2O Glycolysis = 2 ATP/glucose Kreb’s Cycle = 2 ATP/glucose ETC = 32 ATP/glucose 36 ATP/glucose

Cellular Respiration, Sports, and Energy Sources For any athlete to sustain intense activity longer than 90 seconds or so, cellular respiration must come into prominence. Endurance sports such as soccer that involve continuous effort over a lengthy time period rely heavily on cellular respiration. Fats and proteins in addition to glucose are used as energy sources during this phase. During physical exercise, the primary sources of energy are carbohydrates and fats; protein is less accessible and normally contributes only a small percentage of the total energy used. © 2015 Thompson Educational Publishing, Inc.

Exercise Workbook Pg.128 Exercise 7.2 Complete Table for Cellular Respiration

© 2015 Thompson Educational Publishing, Inc. Wrap Up: Nutrients in food need to be resynthesized into a universal form of “free energy,” known as ATP, that can then be used for physiological processes. The body has two systems for resynthesizing ATP: anerobic (without oxygen) and aerobic (with oxygen). Within these two energy systems, there are three main metabolic pathways by which ATP energy reserves are restored: ATP-PC (anaerobic alactic); glycolysis (anaerobic lactic); and cellular respiration (aerobic). © 2015 Thompson Educational Publishing, Inc.

© 2015 Thompson Educational Publishing, Inc. Wrap Up Cont… The ATP-PC (anaerobic alactic) energy pathway yields enough ATP (about one molecule) for about 10-15 seconds of strenuous effort. Glycolysis (the anaerobic lactic energy pathway) yields twice as much ATP compared to the amount of ATP produced in the ATP-PC pathway— two molecules of ATP for every molecule of glucose. The ATP-PC pathway plays an important role in power events that last only a few seconds and require a large burst of energy. Glycolysis plays an important role in activities that involve intense bouts of effort for longer periods of time and are eventually hampered by lactic acid buildup. © 2015 Thompson Educational Publishing, Inc.

© 2015 Thompson Educational Publishing, Inc. Warp Up Cont… The aerobic energy system (cellular respiration) involves molecular activity in the mitochondria of cells and yields 20 times more energy than the aerobic system. Endurance sports such as cross-country skiing and marathon running rely heavily on cellular respiration. The three metabolic pathways in the human body differ in many ways, including their energy source, whether or not they use oxygen, the amount of ATP produced, and the types of exercise that rely on each pathway. © 2015 Thompson Educational Publishing, Inc.

Factors Affecting ATP Energy Production for Life Processes The preceding description of the three pathways is a simplifed representation of the chemistry involved. In real life and everyday activity, the processes and pathways overlap and interact in complex ways. The three metabolic pathways allow our bodies to create sufficient energy to carry out movement as well as all vital processes—neural activity, organ function, breathing, and so on. The precise ways in which these pathways are used for ATP energy production also depends on the individual athlete, the sport the athlete is involved in, and the intensity and duration of physical activity. © 2015 Thompson Educational Publishing, Inc.

© 2015 Thompson Educational Publishing, Inc. A Comparison of the Three Metabolic Pathways in the Human Body © 2015 Thompson Educational Publishing, Inc.

Primary Metabolic Demands of Various Sports Phosphagen system Anaerobic glycolysis Aerobic metabolism Archery High Low   Baseball Basketball Moderate to High Diving Fencing Moderate Field Events Field Hockey Football Gymnastics Ice Hockey Lacrosse Softball Soccer Swimming - Sprint Swimming - Distance Tennis Track - Sprint Track - Distance

Lactic Acid -we know that lactic acid is a painful by product of glycolysis when insufficient oxygen is present -one of the main causes of stopping activity Anaerobic threshold (Blood lactate threshold) Point at which a large increase in blood lactate occurs (compared to resting levels) Onset of blood lactate accumulation (OBLA) Rapid accumulation of blood lactate; always occurs after the lactate threshold

Raising lactate threshold is important in training athletes Anaerobic training – extend point at which the threshold is reached Aerobic training – increase mitochondria and myoglobin levels (oxygen carrying molecule found in muscle fibres)

Which athlete reached the lactate threshold first? At what time did that occur? Which athlete has the best endurance based on the results of the test above? What comparisons can you make between the three athletes?

The Cori Cycle We can’t just think of lactic acid as a bad thing Remember that blood lactate levels don’t ALWAYS increase Therefore the body MUST have a way of ridding itself of lactic acid takes lactic acid (lactate) and converts it to pyruvate in the liver the pyruvate is then converted to glucose/glycogen and re-enters the energy pathways, allowing further production of ATP Better endurance athletes will have a greater ability to convert their lactic acid

© 2015 Thompson Educational Publishing, Inc. Slow-Twitch and Fast-Twitch Muscle Fibres Certain muscles and muscle groups are more adapted to one energy production system than another. Exercise physiologist find it useful to distinguish different kinds of muscle fibres: Slow-twitch muscle fibres are red or dark in colour, and generate and relax tension relatively slowly. The trade-off is that they are able to maintain a lower level of tension for long durations. Fast-twitch muscle fibres are more pale in colour, have the ability to tense and relax quickly, and can generate large amounts of tension with relatively low endurance levels. © 2015 Thompson Educational Publishing, Inc.

Muscle Fibre Types and Physical Activity Slow-twitch muscle fibres These are ideal for activities such as long- distance swimming, cycling, and running. Fast-twitch muscle fibres These can activate at a rate two to three times faster than slow- twitch muscles, making them ideal for the fast, powerful muscle contractions needed for activities such as short sprints, powerlifting, and explosive jumping. © 2015 Thompson Educational Publishing, Inc.

Type I Fibres [Slow-Oxidative (SO) Muscle Fibres] Kinesiologists distinguish not just two but three different types of muscle fibre, using a combination of tension-generating features and the metabolic properties of the fibre. Type I or slow-oxidative (SO) muscle fibres generate energy slowly, are more fatigue- resistant, and primarily depend on aerobic processes. © 2015 Thompson Educational Publishing, Inc.

Type IIA Fibres [Fast-Oxidative Glycolytic (FOG) Fibres] Type IIA or fast-oxidative glycolytic (FOG) muscle fibres are intermediate-type muscle fibres. They allow for high-speed energy release as well as glycolytic capacity. © 2015 Thompson Educational Publishing, Inc.

Type IIB Fibres [Fast-Glycolytic (FG) Muscle Fibres] Type IIB or fast-glycolytic (FG) muscle fibres store lots of oxygen and sufficiently high levels of enzymes necessary for quick contraction without requiring oxygen. © 2015 Thompson Educational Publishing, Inc.

Characteristics of Muscle Fibre Types © 2015 Thompson Educational Publishing, Inc.

© 2015 Thompson Educational Publishing, Inc. The Role of Myoglobin in Sustaining Energy-Producing Reactions The differences in muscle fibre types are due mainly to the extent to which a muscle relies on oxygen in the production of energy. The protein myoglobin is the oxygen storage unit that delivers oxygen to working muscles, thereby enabling energy-producing reactions to be sustained over a long time period. Slow-twitch, red muscle fibres are high in myoglobin and ideal for endurance activities. Fast-twitch fibres (with low myoglobin concentrations) are more adapted to shorter bursts of effort. © 2015 Thompson Educational Publishing, Inc.

So what is the difference between these two athletes? What allows one athlete to excel at running for 5 hours and another to excel at running for 10 seconds?

Implications for Training For elite athletes, differences in muscle fibre types are often very pronounced. Olympic sprinters, for example, may possess as much as 70-80 percent fast-twitch muscle fibres. Athletes in marathon-style events may possess that equivalent in slow-twitch fibres. But many factors contribute to an individual’s athletic performance. Physiology is just one of them. © 2015 Thompson Educational Publishing, Inc.

© 2015 Thompson Educational Publishing, Inc. The Puzzle of East Africans’ Dominance in Distance Running For some time now, athletes from Kenya and Ethiopia have dominated long- distance running. These countries typically account for medals in the 5000 m, the 10 000 m, and the 42.2 km marathon. The achievement of these runners is one of the most puzzling and most studied topics in sport science. © 2015 Thompson Educational Publishing, Inc.

Possible Physiological and Cultural Explanations Some researchers theorize that these athletes’ bodies have a higher capacity to take in and use oxygen—a capacity known as “VO2 max.” Others argue that low overall body fat, long legs, and low resting heart rates help these athletes run faster, longer, and more efficiently. Children in Kenya and Ethiopia tend to walk and run everywhere, thus building up a strong background in long-distance running. Budding athletes in these countries often see running as a means of supporting their families through prize money and endorsements. © 2015 Thompson Educational Publishing, Inc.