THE PHYSIOLOGY OF EXERCISE 1125 Steven C Seideman Extension Food Processing Specialist Cooperative Extension Service University of Arkansas

INTRODUCTION The lack of exercise was never been a problem until the middle of the 20th century when the industrial age, with its automation, replaced much of the physical work in the United States. This module briefly discusses the history, benefits, types and purposes of physical activity.

RECENT POPULARITY Prior to the 1980s, physical education was required in most schools for purposes of preparing the youth for jobs that required physical strength. The majority of the physically demanding jobs decreased and the general population believed that physical exercise was not the best way to spend their leisure time.

RECENT POPULARITY Physical activity was replaced by computer games, television and other non-physical activities. Along with this shift toward less physical activity, came the problems with feelings of stress, obesity, diabetes, heart disease, and rampant depression among other physical problems. The obvious solution is EXERCISE.

RECENT POPULARITY People who exercise today can be divided into several groups; 1)People interested in weight loss 2) People that believe that exercise will increase their longevity. 3) People who believe ”If some exercise is good, more is better” and ultimately become addicted to exercise.

People Interested in Weight Loss If being overweight is caused by excessive caloric intake (a fact) there are two things we can do to remedy it; 1) Reduce our intake (diet) and 2)Burn excess calories via exercise. More information on nutrition can be found elsewhere in this series (Introduction to Human Nutrition; Module 1219). As a guide, 30 minutes of vigorous exercise 3 to 4 times per week is considered a good program to maintain one’s weight.

People That Believe Exercise will Increase Their Longevity There is very little scientific data to support the belief that exercise will increase longevity, however the quality of life will generally improve. For example, if you do not exercise, you may develop diabetes. In today’s world of modern medicine, you may live with diabetes the same number of years as if you didn’t have it, however, you may have your legs amputated, go blind or suffer other circulatory diseases. Longevity tends to be more genetically determined and not altered as much as most believe by lifestyle and exercise.

“If Some exercise is good, more is better” Addicted These are the exercise fanatics. They live to exercise as opposed to exercise to live. These are the people who run several miles a day and occasionally run 26 mile marathons. They get literally “addicted” to exercise.

THE BENEFITS OF EXERCISE

The Benefits of Exercise The benefits of exercise can be divided into several categories; 1) Health Benefits 2) Mental Benefits 3) Physical Benefits

HEALTH BENEFITS 1) Heart Disease and Stroke - Daily physical activity can help prevent heart disease and stroke by strengthening your heart muscle, lowering your blood pressure, raising your HDL (good cholesterol) and lowering your LDL (bad cholesterol), improving blood flow, and increasing you heart’s capacity to work.

Health Benefits 2) High Blood Pressure – Regular exercise reduces blood pressure in people with high blood pressure (hypertension). 3) Diabetes – By reducing body fat, physical activity can help to prevent and control type 2 diabetes. 4) Osteoporosis – Regular weight-bearing exercise promotes bone formation and may prevent many forms of bone loss associated with aging.

Mental Benefits 1) Exercise will reduce depression and anxiety and help you to better manage stress. 2) Promotes better, more restful sleep. 3) Long term, vigorous exercise causes the brain to release “dopamines” which create a feeling of well-being. This is often referred to as a “runners high”. It is your body’s natural “high”. 4) Succeeding at setting a physical activity goal and attaining that goal contributes to a feeling of accomplishment. 5) Self esteem is often raised by reducing ones weight.

Physical Benefits Physical exercise reduces some of the effects of aging. Keeps joints, tendons and ligaments flexible so it’s easier to move around. By increasing muscle strength and endurance and improving flexibility and posture, regular exercise can prevent back pain. By losing weight via exercise, loss weight is suspended in hip, knee and ankle joints thereby increasing their usefulness.

TYPES OF EXERCISE

Types of Physical Activity For weight control and general physical activity, many types of daily activities can help; SPORTS PLANNED EXERCISE PROGRAMS HOUSEHOLD CHORES LAWN WORK All the above have some beneficial effect.

Types of Planned Exercises Exercises are broadly classified as one of two types; 1) Aerobic 2) Anaerobic

Aerobic Exercise Aerobic exercises are those that require a substantial amount of oxygen over an extended period of time and causes you to breathe more deeply and your heart to work harder to pump blood. It is also known as “cardiovascular exercise”. It improves the health of your heart, lungs and overall cardiovascular system. Examples include walking, jogging, running, aerobic dance, bicycling, rowing, swimming and cross-country skiing.

Anaerobic Exercise Anaerobic exercise usually refers to resistance training whereby large amounts of oxygen are not needed. Anaerobic exercise is done primarily for increased muscle mass and bone strength. Examples include weight lifting, sit-ups, push-ups, stretching, etc.

Rate Limiting Steps In aerobic exercises where large groups of muscles are used repeatably over a long period of time, the rate limiting step is the update and utilization of oxygen. In anaerobic exercise, where only single or small localized muscle groups are utilized, the rate limiting step is in the number of sarcomeres present in the muscles used.

The Amount/Type of Exercise Recommended Most experts suggest 30 minutes/day of moderate-intense aerobic exercise 3 or more times per week plus some form of anaerobic exercise twice per week.

HOW TO GET STARTED The single most important ingredient is determination. Decide on the best time of day (morning, noon or evening). Decide on the type of activity (walking, jogging, stretching etc). Set an exercise plan starting slow and easy and building up more as time passes. You don’t need fancy equipment- good shoes and appropriate clothing are enough.

SAMPLE PLAN Here is a get-started simple plan. 1) Get up 1 hour earlier than usual. 2) Do about 10 minutes of serious stretching exercises. 3) Walk vigorously for 30 minutes. 4) Do 10 to 20 sit-ups and push-ups. 5) Shower 6) Go to work. Notice the improvement in attitude and reduced anxiety.

The Physiology of Exercise

The Physiology of Exercise This section will take you through the concept of calories in foods, the body tissues and the biochemistry of exercise .

FOOD Food consists of water, carbohydrates, fats/oils, proteins, vitamins and minerals. Water is by far the most abundant but contains no calories. Vitamins and minerals are present in very small amounts and do not contribute to calories. This leaves us with carbohydrates, fats/oils and proteins.

CALORIES Calories associated with food components; Carbohydrates – 4.5 kcal/gram Proteins- 4.5 kcal / gram Fat- 9 kcal/ gram

Food Components Carbohydrates, fats and proteins are all inter-convertible in the body. This is a very important yet poorly understood concept. If we eat a 3,000 calorie per day diet and only utilize 2,000 calories, the remaining 1,000 will be stored in the body in a priority order, usually as fat. This could conceivably mean that if you ate 3,000 calories of only carbohydrates and protein, it would still be stored as fat if not utilized.

The Burning of Food The Krebs cycle or tricarboxyclic acid cycle utilizes carbohydrates, fats and proteins to generate energy (ATP), CO2 and water (sweat).

PRIORITY OF NUTRIENT UTILIZATION Our body has a priority in which nutrients (carbohydrates, fats and proteins) are utilized by various tissues. 1) Nervous System 2) Skeletal system-bones 3) Muscle 4) Fat

Priority of Nutrient Utilization If we exercise, our nutrient supply is used at the muscle level and fat is never formed. This same priority system reverses when we experience lack of nutrients. We start using fat for energy and then begin to burn muscle as fat stores are depleted.

THE MARATHON RUNNER

THE MARATHON RUNNER Can you imagine what happens as a person runs a 26.25 mile marathon? 1) The first utilized component is glucose in the blood. Blood sugar, or glucose, generally only lasts 15- 20 minutes. When we run low of blood glucose, our brain generally signals us that we are hungry. Immediately before a big race, you often see athletes eating chocolates bars for that instant energy.

THE MARATHON RUNNER 2) As blood glucose starts to bottom out, the runner begins to utilize muscle glycogen. Muscle glycogen are long chain glucose molecules stored in the muscle that look like sand under an electron microscope ( see next slide). This glycogen supply can last 30 minutes to an hour.

The Marathon Runner 3) As the glycogen level becomes lower, the runner starts utilizing fat as energy. We all have stores of fat in various parts of our body. Distance runners generally have very little subcutaneous ( under the skin) fat. Fat is also stored around kidneys, in between muscle groups and even within the muscle.

THE MARATHON RUNNER 4) As the marathon runner begins to run out of easily utilizable fat, they begin to utilize muscle for energy. If not much muscle is used for energy by the runner, they will recover from the run fairly quickly, however, if excessive muscle utilization has taken place, recovery could last over a month.

DIETING The same chain of events (utilization of glucose, glycogen, fat and then muscle) are exactly the same if one goes on a diet. Anorexia Nervosa, a condition where a person is mentally repulsed by food, goes through the above process and if not treated, the person dies from digesting their heart ( a protein).

BODY TISSUES

FAT CELLS Fat is the ultimate storage depot for unutilized energy. Fat cells, call adipocytes are actually cells that develop and become filled with fatty acids. If one exercise, the fatty acids are utilized for energy and one experiences a loss of weight. However, as one “falls off” the diet, the adipocytes refills with fatty acids quite easily. Therefore, to be successful, one must stay on the diet and keep the fatty acids out of the adipocytes for 6 months to a year in order for the adipocyte to disappear.

MUSCLE AND MUSCLE FIBERS

MUSCLE FORMATION Before we were born, our muscle cells formed into fibers whereby at birth our number of muscle fibers were determined and cannot be changed. We can increase the length and diameter of muscle fibers through exercise. Weight lifters subject muscle to increasing loads and repetition whereby the muscle is damaged. After a day or two, they again subject muscle to damage.

Muscle Formation The body responds to this damage by not only repairing itself but repairing itself to resist even damage. Correspondingly, the muscle get larger by adding more, structural components called sarcomeres and by adding more mitochondria.

Muscle Fiber Types All muscle contain muscle fibers that are one of three types. RED, WHITE and INTERMEDIATE Notice the difference between beef (primarily red muscle fibers) vs chicken breast ( primarily white muscle fibers)

Characteristics of Muscle Fiber Types RED -More myoglobin -More fat -More mitochondria -Small in diameter -Aerobic metabolism -Dark in color -High in iron -Less glycogen -Slow twitch but very strong WHITE Less myoglobin -Less fat -Less mitochondria -Large diameter -Anaerobic metabolism -Light in color -Less iron -More glycogen -Fast twitch but weak

Muscle Fiber Types Intermediate muscle fibers are in between red and white in characteristics. All muscles vary by location, type of exercise, function, etc, Some experts claim you can exercise to obtain a certain fiber type ( sprinter vs distance runner) Some experts claim the muscle fibers are genetically determined (take biopsy to determine your ability to either sprint or run distances).

MUSCLE FIBER EXAMPLES Duck breast muscle vs chicken breast muscle. Hummingbird vs crow Beef vs pork vs chicken Support muscles vs muscles used for locomotion.

SUMMARY Physical exercise has many benefits and should certainly become a part of our lifestyle. Understanding how the human body responds to food and exercise at the tissue and cellular level is important to developing a well-rounded exercise program including both aerobic and anaerobic types.