“When it comes to health and well-being, exercise is about as close to a magic potion as you can get.”

-Thich Nhat Hanh, Zen Master, poet, and peace advocate

Lately you may have heard that “sitting is the new smoking.” A sedentary lifestyle is related to an increase in the incidence of almost every chronic disease or condition, and has many, many negative health consequences. Lack of regular physical activity costs us about $117 billion per year in additional health care costs. Although smoking is still much more dangerous to your health than sitting, the good news is that fewer people smoke. However, almost 80% of US adults are not meeting the minimum amount of both the aerobic and muscle strengthening activity recommended for good health, and half do not meet just the aerobic activity guidelines.¹ Health is a human condition with physical, social, and psychological dimensions, each characterized on a continuum with positive and negative poles. Positive health is associated with a capacity to enjoy life and to withstand challenges; it is not merely the absence of disease. Negative health is associated with illness, and at the extreme, premature death.¹ Physical activity contributes to positive health, and people of all ages and body types can be physically active.

12.1 Introduction to Nutrition and Physical Fitness

Physical fitness is defined as the ability to carry out daily tasks with vigor and alertness, without undue fatigue, and with ample energy to enjoy leisure-time pursuits and respond to emergencies.¹ Physical fitness is generally achieved through moderate to vigorous physical exercise, physical activity, sufficient rest, and proper nutrition. Before the industrial revolution, fitness was defined as the capacity to carry out the day’s activities without undue fatigue. However, with automation and changes in lifestyles, physical fitness is now considered a measure of the body’s ability to function efficiently and effectively in work and leisure activities, to be healthy, to resist hypokinetic (low movement) diseases, and to meet emergency situations. Physical fitness has multiple components related to overall health, including cardiorespiratory fitness (endurance or aerobic power), musculoskeletal fitness, flexibility, and balance.¹ Body composition, which is the ratio of body fat to lean tissue, also plays a role. There are also components of fitness related less to health and more to athletic performance. These skill-related components include agility, reaction time, speed, power, and coordination.

Health-Related Components of Physical Fitness²:

• Cardiorespiratory Endurance. This is the ability of your heart, lungs, blood, and blood vessels to meet body needs both at rest and during activity. Most aerobic activities promote this aspect of fitness. Physical activities that promote cardiorespiratory endurance do so by increasing heart rate and breathing rate over a period of time, keeping your cardiac and respiratory systems functioning at an optimal level. Exercises that increase your cardiorespiratory endurance are activities such as fast walking, jogging, swimming, and other things that raise your heart and breathing rate.¹
• Muscle Strength and Endurance. A muscle’s ability to perform a maximum contraction one time is a measure of strength while a muscle’s ability to perform sustained work is considered endurance.³ Strength and endurance exercises strengthen muscles by breaking apart and re-building muscle cells. These help to build and maintain muscle and bone mass. Activities that promote this are resistance training, such as weight lifting or calisthenics.
• Flexibility. This is the capacity of the joints to move through a full range of motion; the ability to bend and recover without injury. Physical activities that increase this freedom of movement are ones that promote the movement of joints, such as yoga, and a variety of stretches.
• Balance. This is the ability to control the body’s position, either stationary or while moving.³ Balance exercises are especially needed by older adults who have a higher risk of falling. These activities help to strengthen the muscles, specifically in the lower extremities, that are involved in maintaining balance, including activities such as calf raises, and standing on one foot.¹
• Body Composition. Though not a physical activity, body composition is an important part of fitness. It is the ratio of fat to lean tissue in your body, and we strive for more lean body tissues and less fat. It is important to recognize though, that fat is an important tissue in our body, and is essential to life, just not in excess.

Physical activity refers to any bodily movement produced by the contraction of skeletal muscle that increases energy expenditure above a basal level. Examples of physical activity include activities of daily living such as climbing stairs, doing housework, walking the dog, and walking at the workplace. Exercise is a form of physical activity that is planned, structured, repetitive, and performed with the goal of improving health or fitness. Although all exercise is physical activity, not all physical activity is exercise.

Activity guidelines

The Physical Activity Guidelines for Americans (PAGs) developed as a collaboration among various governmental and professional agencies. These groups looked at the scientific evidence about the role of physical activity in health, and developed guidelines and recommendations for the general public. This publication suggests that all adults should avoid inactivity in order to promote good health mentally and physically. For substantial health benefits, the recommended duration (time) of exercise for adults is 150 to 300 minutes (2.5 to 5 hours) per week of moderate intensity, or 75 to 150 minutes (1.25 to 2.5 hours) a week of vigorous intensity aerobic physical activity, or an equivalent combination of moderate and vigorous intensity aerobic activity. Preferably, exercise bouts should be spread throughout the week. While there is no minimum requirement for duration of a single bout, the total amount of time spent should meet the duration guidelines. Additional health benefits are gained by engaging in physical activity beyond this amount. Adults should also do muscle strengthening activities that are moderate or high intensity and involve all major muscle groups on two or more days a week, as these activities provide additional health benefits. Children aged 3-5 years should be physically active throughout the day and caregivers should encourage varied and moderate to vigorous intensity play. School-aged youth (6-17 years) should participate in a combination of aerobic and muscle strengthening activities for 60 minutes or more each day.¹ There are many ways to add physical activity to your day. You could take the stairs instead of the elevator or escalator, park further away from your destination (when safe to do so), ride a bike or walk instead of driving, dance around your living room to your favorite tunes, or play outside with your family and friends. You can even join a gym or subscribe to an online fitness app so that you don’t have to leave home to participate. Find some activity you enjoy, and then just do it!

Frequency, intensity, time (duration), and type are the components of a robust aerobic physical fitness program. Frequency refers to how often you exercise. This will vary based on your personal goals and availability, but it is recommended that exercise sessions (bouts) should be spread out about 3 to 5 times throughout the week. Intensity is an estimate of how hard you’re working in the exercise bout and there are several ways to measure this. Time or duration is how long the bout lasts. The type of exercise you choose to do will help to determine the benefits received. An easy way to remember these four components is by the acronym FITT (frequency, intensity, time, type).

Muscle strengthening activities have three components: frequency (how often), intensity (how much weight or force is used), and sets/repetitions (comparable to duration and time). Improvements occur in fitness when one or more of these components is increased, a concept called overload. When asked to do more, the body adapts so that it is better able to meet the demands the next time. Small, continual changes in overload with subsequent adaptation is called progression. These small improvements in the body’s ability to respond to imposed stressors over time minimizes the chances of injury and leads to fitness. Movement also has specificity—only those muscles and organs most used will adapt and improve.

How to Determine Intensity Level of Aerobic Activity

The intensity of aerobic exercise is an estimate of how physically difficult and strenuous an exercise bout is to complete. There are many ways to determine intensity level, and there is an inverse relationship between the level of intensity and the duration of the bout required for benefits. This means that as intensity goes up, duration can go down to achieve similar benefits. One way to determine intensity is to use a person’s heart rate. As you are sitting here reading this you have a certain heart rate. If you put your two fingers on the carotid artery near the front of your neck, on the radial artery on the inside of your wrist, or your hand on your chest, you can feel your heartbeat or pulse. If you count the number of beats in one minute you will have an approximation of your resting heart rate (RHR). Instead of using your fingers to feel your pulse, you could use technology to

measure it such as wearable fitness or heart rate monitors. Your heart rate will increase at about the same rate that intensity of exercise increases, so it is a good estimate of the intensity of movement. While your lowest heart rate while awake is considered your RHR, your “maximum” heart rate is estimated to be 220 minus your age in years. So if you are 20 years old, your estimated maximum heart rate is 220-20 = 200 beats per minute (bpm). Your maximum heart rate is far too high for you to try to sustain during exercise. Instead, there are “target heart rate zones” you can aim for. If you wish to be working out at a moderate level of intensity you will want your heart rate to be between 64-76% of your maximum. If you wish to be working out at a vigorous level of intensity then you will want your heart rate to be between 77-93% of your maximum.⁴ Using the 20 year old example again, if 200 is your maximum heart rate then

1. 200 x 0.64 = 128 bpm for 64% of maximum and
2. 200 x 0.76 = 152 bpm for 76% of maximum.

This tells you that if you check your pulse during exercise and you count between 128-152 bpm you are exercising at moderate intensity.

Another much easier (though less precise) way to estimate intensity level is the “talk test” which is a measure of how the intensity affects your breathing. Just like with heart rate, breathing (or respiratory) rate will rise as exercise intensity rises, though not as linearly. Basically, if you are able to carry on a breathy conversation as you exercise, but you are not able to sing, you are probably at a moderate level of intensity. If you cannot say more than a few words without taking a breath, you are “out of breath” and are probably at a vigorous level of exercise. If you can sing all of the words to a song easily, you are at a low level of intensity which may not confer the benefits you seek. Many people prefer this method because it doesn’t require any equipment nor does it require you to stop to count your heart beats.⁵

A third way to estimate exercise intensity is to use the Borg Scale of Perceived Exertion. This is your level of perception of how hard the exercise feels to you. As you exercise, you would take into consideration your breathing rate, how your muscles feel, and how much you are sweating, and rank the difficulty of your current exercise on a rating scale from 6-20. This is called your Rate of Perceived Exertion (RPE) where 6 is no exertion at all, and 20 is maximal exertion. Moderate intensity exercise would be considered “somewhat hard” which corresponds to RPE 12-14. With practice, one can become accustomed to how the body feels at various intensities of exercise, and adjust accordingly. For example, if a walker is able to breathe easily, they might rank themselves at an 8 on the RPE scale and start to walk faster to achieve moderate intensity. If they rank themselves, however, at an 18, they may slow down a bit so that they are able to complete the duration of the exercise session. Although subjective, this might provide a good estimate of your actual heart rate during exercise by multiplying the RPE level times 10. So a RPE of 14 would indicate an approximate heart rate of 140 bpm. RPE may be especially useful for people who are taking medications which affect their heart rate.⁶

Table 12.1.1 Rating of Perceived Exertion (RPE)

Benefits of Fitness

There are several proven benefits of physical fitness for overall health and well-being, and almost the entire body is affected including the brain. Even small changes in the frequency or duration of physical activity can provide many benefits. And experts say some physical activity is better than none. Benefits from an exercise bout are both acute and chronic. Acute benefits such as lowered anxiety, improved sleep, reduced blood pressure, improved insulin sensitivity, and some aspects of cognitive function occur immediately or shortly after a bout while chronic benefits such as reduction in the occurrence of chronic disease like cancer, heart disease, and type 2 diabetes occur long term.¹

There is strong scientific evidence that physical activity delays death from all causes. Activity reduces the risk of dying prematurely from chronic diseases such as cardiovascular disease and cancer. Those that meet the minimum requirements of 150 minutes per week of moderate intensity activity see as much as a 33% reduction in risk of premature death. As daily sitting time decreases and levels of moderate intensity physical activity increases, mortality from all causes decreases.⁷ The PAGs categorize people into four groups: inactive, insufficiently active, active, extremely active. The greatest relative benefits occur in those going from inactive to insufficiently active, so doing something is better than doing nothing.⁸ The following list of benefits is adapted from the PAGs¹:

• Cardiorespiratory Benefits. Physical fitness has proven to result in positive effects on the body’s blood pressure because staying active and exercising regularly builds a stronger heart. Blood pressure is indicated by two numbers, with one on top of the other. The heart is the main organ influencing both systolic blood pressure (top number) and diastolic blood pressure (bottom number). For a review of blood pressure see Chapter 7. Engaging in physical activity will create a rise in blood pressure, once the activity is stopped, however, the individual’s blood pressure will return to normal. The more physical activity that one engages in, the easier this process becomes, resulting in a more ‘fit’ individual. A “healthy” blood pressure is considered to be 120/80 or below. Through regular physical fitness, the heart does not have to work as hard to create a rise in blood pressure, which lowers the force on the arteries, and lowers the overall blood pressure. It also improves the lipid profile of individuals, improving the levels of HDL (good) cholesterol.
• Weight Management. As we saw in Chapter 9, being overweight contributes to the development of chronic diseases and conditions. Participating in regular physical activity can help maintain your weight, and if you’ve lost weight, help you keep it off. However, some people may require more than the 150-300 minutes of exercise per week to achieve their desired results, and diet plays a major role as well. For weight loss the best long term results are achieved with a combination of caloric restriction and physical activity. We also see weight maintenance benefits in children participating in regular physical activity.
• Bone and Muscle Benefits. The bones of children and older adults benefit the most from regular activity. Children who run, jump, and play have higher bone densities than those who are sedentary. Physical activity also helps preserve bone mass in older adults. Increases in muscle mass, power, and strength can improve balance and agility. This “functional ability” improves the quality of life for many, allowing older adults to move more easily, play with grandchildren, and fall less often.
• Brain function. A Greek proverb says that “a sound mind is in a sound body.” The mind-body connection has been touted for thousands of years, and now science helps to prove it. Acute benefits of physical activity include improved academic performance and memory in children, and in both children and adults reduced anxiety and improved sleep outcomes. Regular exercise is also effective for cognitive function in older adults. It can reduce the age-related decline in cognition and improve overall function like memory, processing speed, and executive function (such as decision making). Exercise also has persistent antidepressant and antianxiety effects in children and adults. Older adults who exercise regularly report having a better quality of life.
• Cancer Prevention. Physically active adults have a significantly lower risk of developing cancer of the bladder, breast, colon, endometrium, esophagus, kidney, lung, and stomach regardless of weight status. While the mechanisms are not always clear, what is clear is the beneficial relationship between regular exercise and cancer prevention.
• Other Health Benefits. Those with chronic diseases or disabilities can benefit from participation in regular physical activity including those with osteoarthritis, type 2 diabetes, dementia, multiple sclerosis, spinal cord injury, stroke, and others. Besides decreasing pain and improving functional ability, most report an improved quality of life.

12.2  Energy for Muscle Contraction

Each day the human body needs energy. This energy is used to fuel all bodily activities—both those you can see and those you cannot. At rest the body expends about 1-1.5 kcal/minute, but once we start to move the demands for energy can increase dramatically, up to 35 kcal/minute. Therefore we will address how these energy producing systems work during exercise, keeping in mind that most also work when the body is at rest. We can use the analogy of the mechanical engine to illustrate how this works. Although muscles and engines work in different ways, they both convert chemical energy into energy of motion. An automobile engine uses the stored energy of gasoline and converts it to heat and energy of motion (kinetic energy). Muscles use the stored chemical energy of food we eat and convert that to heat and kinetic energy. We need energy to enable growth and repair of tissues, to maintain body temperature, to think and breathe and have our heart beat, and to fuel physical activity. Energy comes from kcal containing foods rich in carbohydrate, protein, and fat.

Origins of the Energy for Muscle Contraction

Like the dollar is the currency of commerce in the US, adenosine triphosphate (ATP) is the currency of energy in our bodies, the body’s biochemical way to store and transport energy. ATP is made up of an adenosine molecule attached to three phosphate molecules. However, ATP is not stored to a great extent in cells. We “spend” ATP to pay for our muscle contractions by splitting off one of the phosphate molecules, turning ATP into adenosine diphosphate (ADP) plus energy from the splitting of the chemical bond that held the third phosphate molecule to the adenosine molecule. So once muscle contraction begins, the making of more ATP must start quickly. To make ATP, several systems generate energy to reattach the missing phosphate to change ADP back into ATP. This is similar to how your cell phone battery is recharged when you plug it into an electrical outlet. Since ATP is so important, the muscle cells have several different ways to do this recharging. These systems work together in phases. The three biochemical systems for producing ATP for muscle contraction are, in order:

1. Using creatine phosphate (CP)
2. Using glycogen
3. Aerobic respiration

Creatine Phosphate

All muscle cells have a little ATP within them that they can use immediately—but only enough to fuel contraction for a few seconds! All muscle cells contain a high-energy compound called creatine phosphate (CP) which is made of a creatine molecule plus one phosphate. To regenerate the ATP, the enzyme creatine kinase splits CP into creatine and phosphate. The released phosphate attaches to ADP to form ATP. Because the CP is in the muscle cell, this process can occur very quickly after the onset of contraction, at a very high rate and without the presence of oxygen, so the process is considered anaerobic. However, there is limited CP in each muscle cell, and each CP can only regenerate one ATP, so CP can supply the energy needs of a working muscle, but only for about 8-10 seconds. If physical activity continues beyond these few seconds (and it usually does), additional systems are required to continue the regeneration of ATP.

Glycogen (Anaerobic Glycolysis)

Fortunately, muscles also have large stores of a carbohydrate called glycogen which can be used to regenerate ATP from glucose. You may recall from Chapter 5 that glucose is a ringed structure containing six carbons along with hydrogen and oxygen atoms. To create ATP in this process, this six carbon glucose is split in half, making two three-carbon molecules. But this takes about 12 chemical reactions so it supplies energy a bit more slowly than making ATP from CP.  However, it nets two ATP for every glucose that is split versus the one per CP. It’s still pretty rapid though and will produce enough energy to fuel activity lasting about 90 seconds. Oxygen is not needed (anaerobic reaction)—this is great, because it takes the heart and lungs some time to get increased oxygen supplied to the muscles.

At the end of this process, the two three-carbon molecules produced are called pyruvate. If additional ATP are required, and oxygen is available, this pyruvate can be further broken down in aerobic respiration. However, if necessary oxygen is not yet available, this pyruvate can be converted to a substance called lactate (lactic acid). You know when your muscles are accumulating lactic acid because it causes fatigue and a “burning” sensation.

Aerobic Respiration (with Oxygen)

Within one to two minutes of the onset of exercise, the heart and lungs have caught up to the demand placed on them, and the circulatory system starts to supply working muscles with the additional oxygen required. When oxygen is present, aerobic respiration (sometimes called cellular respiration) can take place to break down energy nutrients to make ATP. These energy nutrients serve as fuel and can come from several places:

• pyruvate remaining after anaerobic glycolysis
• remaining glycogen in the muscle cells
• glucose from food digestion
• glycogen from the liver
• fatty acids from fat reserves in the muscles and adipose tissue
• amino acids from the body’s muscles (when glucose is unavailable)

Aerobic respiration takes even more chemical reactions to produce ATP than either of the two systems discussed previously. It occurs in the mitochondria of cells, often called the cell’s “powerhouse,” and is the slowest of all three systems—but it can supply ATP for several hours or longer, as long as the supply of fuel lasts. It uses the Kreb’s Cycle (also called the Citric Acid Cycle or Tricarboxylic Acid Cycle [TCA cycle]) and the electron transport chain to generate ATP. To keep the Kreb’s cycle turning, pyruvate is required, so it is imperative that the body has enough glycogen stored to maintain aerobic respiration during physical activity. Although fat is the largest supplier of ATP during aerobic respiration (both at rest and during aerobic exercise), it requires more oxygen to regenerate the ATP than does glucose. When oxygen delivery lags or is not adequate for fat metabolism, glucose must be used.

Here’s an example of how it works:

Let’s say you have missed the bus and start running to school for a 9:00 am exam:

• For the first 3 seconds of your run to the school, your muscle cells use the ATP they have stored within them.
• For the next 8-10 seconds, your muscles use CP stores to provide ATP.
• You’re 10-15 seconds into your run, since you haven’t made it to school yet, the glycogen system (anaerobic glycolysis, which doesn’t need any oxygen) kicks in.
• Still not there at the 60-90 second mark, so aerobic respiration takes over. At this point, you’ll be breathing more rapidly and your heart rate increases to get that oxygen to the working muscles in order to create ATP. Aerobic respiration will continue to provide the bulk of the required ATP until you arrive at your destination.

The aerobic and anaerobic systems work simultaneously, and the intensity and duration of the physical activity determine the relative contribution of each. Short duration high intensity activities (like sprinting or powerlifting) rely on the anaerobic pathways which supply short bursts of quick energy. Endurance exercise of lower intensity and longer duration relies most heavily on the aerobic system which can supply continuous, sustained ATP to the working muscles.

Hitting the Wall

Have you ever heard of an endurance athlete “hitting the wall” or “bonking”? During very long duration endurance exercise it can be difficult for the body to continue to supply ATP to working muscles because glycogen stores become depleted, thus depleting the supply of pyruvate to keep the Kreb’s cycle turning. When the supply of ATP diminishes, muscles become fatigued and the athlete is no longer able to continue, “hitting the wall.” To reduce the chances of this happening, endurance athletes may consume glucose during the race in the form of a sports drink, energy bars, or energy gels. This almost immediately supplies the needed glucose so that aerobic respiration can continue.

Training

Physical training is the specific use of exercise to promote fitness and strength. Training is specific or task-oriented, and is a person’s ability to perform in a specific activity with reasonable efficiency, for example, sports or military service. Specific training prepares athletes to perform well in their sports. As discussed previously, in order to benefit from physical activity there must be overload, progression, and specificity. To become an elite tennis player, for example, you need to play a lot of tennis! Playing tennis provides you with the skills you need eye-hand coordination, agility, speed, and power. However, you also need to have a high level of aerobic fitness which may come from distance running, adequate muscle strength and endurance that can be gained by resistance training, high amounts of flexibility and balance which can be achieved by practicing yoga or regular stretching. There are many examples of types of training that can be used to gain the specific benefits you seek, and you can find training protocols in books, magazines, web sites, blogs, podcasts, and from professional trainers, exercise physiologists, and coaches. Most protocols involve a mix of both aerobic and anaerobic activities to maximize the adaptations.

Training for a specific sport or activity would most certainly require more than 150-300 minutes per week of training, so the PAGs would not apply. However, the basic physiological adaptations that occur are the same, albeit at different rates and to different degrees, in an inactive person who starts to move a little more, and in an athlete training for a sport. As the body adapts to the overload and progression of activity, several changes in the body’s physiology occur. Used muscles increase in size and become stronger, a process called muscle hypertrophy. Blood vessels expand, and the number of red blood cells and amount of blood plasma increases, allowing the body to take up more oxygen from the lungs and deliver it to working muscles for aerobic respiration. There is an increase in the number of mitochondria in the muscle cells, allowing for more efficient use of the delivered oxygen and more production of ATP via aerobic respiration. All of these adaptations allow you to exercise longer, at higher intensities, lifting more weight or using more force, at a lower RPE. The good news is that it does not take long to begin to experience these adaptations. Many new exercisers begin to see benefits after only a few weeks. The bad news is that these adaptations are not permanent. If the body no longer experiences the overload, or there is no progression, no further adaptations will occur. If you discontinue your exercise program, you will lose those beneficial adaptations.

12.3 Nutrients Important for Athletes

Becoming an elite athlete requires good genes, good training and conditioning, and a sensible diet. Optimal nutrition is essential for peak performance. Nutritional misinformation can do as much harm to the ambitious athlete as good nutrition can help. An individual involved in a general fitness regimen (ex. 30-40 min/day, on most days of the week) can meet their nutritional needs by adhering to a balanced diet. However, athletes involved in moderate or high frequency training programs will need to increase their intake to meet nutritional requirements.

Athletes achieve peak performance by training and eating a balanced diet including a variety of foods. Carbohydrate and fat provide fuel for the body. The use of fat as a fuel source depends on the intensity and duration of the exercise, as well as the condition of the athlete. Exercise may increase the athlete’s need for protein. Adequate water is critical for athletes. Dehydration can cause muscle cramping and fatigue, and increases the risk for heat stroke.

Carbohydrates

Carbohydrates are an important fuel source. In the early stages of moderate exercise, carbohydrates provide 40-50% of the energy requirement. As work intensity increases, carbohydrate utilization increases. The conversion of carbohydrate to energy requires less oxygen than the conversion of fats. Because oxygen is often the limiting factor in long duration and high intensity events, it is beneficial for the athlete to use the energy source requiring the least amount of oxygen per kcal produced. In general, depending on the intensity, duration, and frequency of exercise, athletes should consume between 6-10 g of carbohydrates per kg of body weight per day (remember, 1 kg equals 2.2 lb). Carbohydrate requirements are also affected by the athlete’s sex and body mass, as well as total daily energy expenditure and environmental conditions.

Recall from Chapter 5 that complex carbohydrates come from foods such as potatoes, beans, vegetables, whole grain pasta, cereals and other grain products. Simple carbohydrates are found in foods such as fruits, milk, honey, and sugar. During digestion, the body breaks down all carbohydrates to glucose, which is then utilized for energy or converted to glycogen and stored in the muscles and liver to fulfill later energy needs.

During exercise, stored glycogen is converted back to glucose and used for energy. The body can only store a finite amount of carbohydrates as glycogen. The ability to sustain prolonged vigorous exercise is directly related to initial levels of muscle glycogen. For events lasting less than two hours, the glycogen stores in muscles are typically sufficient to supply the needed energy. Extra carbohydrates will not help any more than adding gas to a half-full tank will make a car go faster.

For events that require higher intensity exercise for more than two hours, a high-carbohydrate diet eaten for two to three days before the event allows glycogen storage spaces to be filled. Endurance athletes, such as long distance runners, cyclists, swimmers, and cross-country skiers, report benefits from a pre-competition diet in which 70% of the calories come from carbohydrates. More about this process will be discussed later in this chapter.

Research has demonstrated that endurance athletes on a high-carbohydrate diet can exercise longer than athletes eating a low-carbohydrate, high-fat diet. However, continually eating such a high-carbohydrate diet is not advised. This conditions the body to use only carbohydrates for fuel and not the fatty acids derived from fats.

For continuous activities of three to four hours, it is important that glycogen stores in the muscles and liver are at a maximum. Additionally, taking carbohydrates during the event in the form of carbohydrate solutions, such as sport drinks containing glucose and electrolytes like sodium and potassium can be beneficial. The current recommendation is a 6-8% glucose solution. Sports drinks can be used to supply sodium and glucose if the athlete tolerates them, but other electrolytes are not essential until after the event. Athletes should experiment during training to find if electrolyte beverages are right for them.

Protein

When compared to fat and carbohydrates, protein contributes minimally to energy needs for the body. Dietary protein is digested into amino acids, which are used as the building blocks for the different tissues, enzymes, and hormones that the body needs to function. It is important for muscle building and repair that occurs after exercise.

Exercise may increase an athlete’s need for protein, depending on the type and frequency of exercise. The current RDA for protein is 0.8 g per kg body weight per day. However, the Academy of Nutrition and Dietetics (AND) and the American College of Sports Medicine (ACSM) recommend that endurance athletes eat between 1.2-1.4 g of protein per kg of body weight per day and resistance and strength-trained athletes eat as much as 1.2-1.7 g protein per kg of body weight.

For example, if you are a distance runner who weighs 185 pounds, we could calculate the recommended grams of protein using 1.2-1.4 g/kg:

1. Convert pounds to kilograms: 185 lb ÷ 2.2 lb/kg = 84 kg
2. Calculate grams of protein: 84 kg x 1.2 g/kg = 100 grams; 84 kg x 1.4 g/kg = 117 g

Consume 100-117 g of high quality protein per day from a variety of both animal and plant sources.

Eating protein after an athletic event has been shown to support muscle protein synthesis. However, eating protein in excess of nutritional needs has not been shown to further increase muscle building. Extra protein not required for muscle building or repair is broken down and used for energy or if additional energy is not required, the nitrogen is stripped from the extra protein, leaving the remaining parts to be stored as fat.  Thus high-protein diets increase the water requirement necessary to eliminate the nitrogen through the urine. Consuming excess protein instead of necessary carbohydrates and fats can deprive an athlete of these more efficient fuel sources, and can lead to dehydration.

A varied diet should provide more than enough protein as caloric intake increases. Protein and amino acid supplements are unnecessary and not recommended. Some athletes turn to protein/amino acid supplementation in the form of powders or pills to fulfill protein requirements. However, this is typically excessive, because protein needs are easily met in an American diet. Eating whole foods instead of supplements is generally the best practice. Consuming supplements in place of meals is generally not recommended. Athletes should consult with their doctor or a registered dietitian before continuing. Additionally, as discussed in Chapter 6, vegan athletes should work with a registered dietitian to make sure their protein intake is sufficient.

Lipids

Fat is also a significant contributor to energy needs for athletes. Remember, it supplies 9 kcal/g, making it the most energy dense macronutrient. During ultra-endurance events, lasting 6-10 hours, fat can contribute 60-70% of energy requirements.

As discussed previously, using fat as fuel depends on the event’s duration and the athlete’s condition. As duration increases and/or intensity decreases, the utilization of fat as an energy source increases. For moderate exercise, about half of the total energy expenditure is derived from free fatty acid metabolism. If the event lasts more than an hour, the body may use mostly fats for energy. Furthermore, trained athletes use fat for energy more quickly than untrained athletes.

Fat consumption should be a minimum of 20% of total kcal intake to preserve athletic performance. Maintaining adequate fat intake is crucial to meeting nutritional needs of essential fatty acids (omega-3 and omega-6) and fat-soluble vitamins (A, D, E and K). Athletes who are under pressure to achieve or maintain a low body weight are susceptible to using fat restriction and should be told that this may hinder their performance. While adequate fat intake is necessary, claims that suggest a high-fat, low-carbohydrate diet enhances athletic performance have not been supported by research.

Vitamins

Maintaining adequate levels of vitamins and minerals is important for bodily function, and therefore, athletic performance. As the activity level of an athlete increases, the need for different vitamins and minerals may increase as well. However, this need can be easily met by eating a balanced diet that includes a variety of foods. There is no evidence that taking more vitamins and minerals than is obtained by eating a variety of foods will improve performance.

B vitamins, including thiamin, riboflavin and niacin, are essential for producing energy during anaerobic glycolysis and aerobic respiration. Carbohydrate and protein foods are excellent sources of these vitamins. B vitamins are water-soluble, which means they are generally not stored in the body, so toxicity is typically not an issue (when consumed from food). Some female athletes may lack riboflavin, so it is important to ensure adequate consumption of riboflavin-rich foods, like milk. Milk products not only increase the riboflavin level but also provide protein, calcium, and vitamin D.

Vitamin D has many functions in the body, and is crucial for calcium absorption. Because a large amount of vitamin D is obtained through sun exposure, athletes who train indoors for prolonged periods of time should ensure that they consume adequate amounts of vitamin D through diet. Dietary sources of vitamin D include mushrooms, fortified dairy or soy, fatty fish, and egg yolks.

Exercise increases the oxidative stress on the body, increasing the need for vitamins C and E, which have an antioxidant effect. Vitamin E is a fat-soluble vitamin, found in fats in the diet such as nuts, seeds, and vegetable oils. When an individual consumes excess fat-soluble vitamins (A, D, E and K), they are often stored in fat throughout the body. Because they are stored, excessive amounts of fat-soluble vitamins may have toxic effects, particularly when obtained from dietary supplements. Chapters 14-16 provide an overview of the functions and dietary sources of vitamins.

Minerals

Minerals play an important role in athletic function. Heavy exercise affects the body’s supply of sodium, potassium, iron, and calcium.

Sodium is lost through the course of an athletic event through sweat, so it may be necessary to replace sodium in addition to water during long duration, higher intensity exercise. Like sodium, potassium levels can also decline during exercise, though losses are not as significant. Both of these minerals can be replaced during exercise through consumption of a sports drink, or after exercise through the diet. It is not necessary to consume sodium such as salt tablets after competition and workouts, and it is not advised. This will draw water out of the cells, causing weak muscles. Good sodium guidelines are to: 1. avoid excessive amounts of sodium in the diet and 2. consider consuming beverages containing sodium during endurance events (>2 hours). Eating foods such as lentils, raisins, potatoes, beans, oranges, bananas, and spinach throughout training and after competition supplies necessary potassium.

Iron carries oxygen via blood to all cells in the body. Needs for this mineral are especially high in endurance athletes. Female athletes and athletes between 13 and 19 years old may have inadequate supplies of iron due to menstruation and strenuous exercise. Female athletes who train heavily have a high incidence of amenorrhea (the absence of regular, monthly periods) and usually have reduced iron stores. Choosing foods high in iron such as red meat, lentils, dark leafy greens, and fortified cereals can help prevent iron deficiencies, but taking an iron supplement may be advised. It is best to consult a physician before starting iron supplements.

Calcium is important in bone health and is required for muscle contraction. All athletes should have an adequate supply of calcium to prevent bone loss. Inadequate calcium levels may lead to osteoporosis later in life. Female athletes are more likely to have inadequate calcium consumption. Low-fat dairy products are a good source of calcium. They also supply vitamin D which is required for the deposition of calcium in bones.

An overview of functions and food sources of minerals is in Chapters 14-16.

Pre-Workout Dietary Consumption

You don’t need expensive “pre-workout” shakes or supplements, but eating before a workout or competition can increase performance when compared to exercising in a fasted state. A pre-workout meal three to four hours before the event allows for optimal digestion and energy supply. Most authorities recommend small pre-game meals that provide 500 to 1,000 calories. This meal should be sufficient but not excessive, so as to prevent both hunger and undigested food. The meal should be high in starch, which breaks down more easily than protein and fats. The starch should be in the form of complex carbohydrates (breads, cold cereal, pasta, fruits and vegetables). They are digested at a rate that provides consistent energy to the body and are emptied from the stomach in two to three hours. High-sugar foods, however, lead to a rapid rise in blood sugar, followed by a decline in blood sugar and less energy. In addition, concentrated sweets can draw fluid into the gastrointestinal tract and contribute to dehydration, cramping, nausea and diarrhea, and therefore are not recommended.

Pre-workout meals should be low in fat. Fat takes longer to digest, as does fiber- and lactose-containing meals. The meal should also contain a little protein. Take in adequate fluids during this pre-workout time. Carefully consider caffeine consumption (cola, coffee, tea) as it may lead to dehydration by increasing urine production. It is important to eat familiar foods before an event, so it is known that they can be tolerated before exercise. Smaller meals should be consumed if less time remains before an event. If a competition is less than two hours away, athletes may benefit from consuming a liquid pre-game meal to avoid gastrointestinal distress. A liquid meal will move out of the stomach by the time a meet or match begins. Remember to include water with this meal. Suggestions for pre-workout meals or snacks include hummus with pita bread or vegetables, cottage cheese with fruit, oatmeal with peanut butter and fruit, rice cakes with nut butter, smoothies with two cups of vegetables and one cup of fruit, or 3-4 oz of salmon or poultry with roasted vegetables and brown rice.

Post-Workout Dietary Consumption

Regardless of age, gender or sport, the post-workout meal recommendations are the same. Following a training session or competition, a small meal eaten within 30-minutes is very beneficial. The meal should be mixed, meaning it contains carbohydrate, protein, and fat. Suggestions for post workout snacks include whole wheat toast with peanut butter and banana, hard boiled eggs with toast or oatmeal, graham crackers or rice cakes with nut butter, chocolate milk, or any of the pre-workout snacks discussed previously. For a post-workout meal try a roasted vegetable stuffed pita with hummus, an omelet with vegetables including potatoes and avocado, or 4 oz of fish, poultry, beef, or tofu with a baked sweet potato and a salad.

Protein synthesis is greatest during the window of time immediately following a workout and carbohydrates will help replete diminished glycogen stores. However, consuming food within the 30-minute window may be difficult for athletes—they may experience nausea or lack of hunger. Options to address this difficulty include:

• Consuming a drink that contains carbohydrates and protein. There are several liquid smoothies and beverages on the market that provide high protein and carbohydrates for replenishment. One classic is chocolate milk.
• If that is difficult, fruit, bread, crackers, or popsicles would all be better than not consuming any food.

Athletes should be wary of ergogenic aids that claim to enhance athletic performance. Many of these claims are unsubstantiated, and some aids may be dangerous or hinder performance. Chapter 17 will address ergogenic aids for athletes and dietary supplements in general.

*The majority of information in this section (12.3) is derived from the Position paper of Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance.⁹

12.4 Special Considerations for Sport

Carbohydrate Loading (Glycogen Supercompensation)

Carbohydrate loading is a diet strategy that involves greatly increasing carbohydrate intake before high-intensity, long duration physical activity. Marathon runners, endurance swimmers, long distance triathletes, cross-country skiers, and cyclists are the athletes that benefit the most from carbohydrate loading. Most other athletes do not need to carbohydrate load, as the body can use its existing energy storage for most recreational activity.

The goal is to “supercompensate” or overload the glycogen storage system in muscles so that you will have plenty to draw from throughout the exercise bout such as running a marathon. To load the muscles with glycogen, the athlete consumes a high-carbohydrate (but low-fiber) diet of about 7-12 g per kg of body weight for a few days before a high-intensity athletic event. At the same time, the athlete should reduce their physical activity to rest up for the event, thus helping to maintain stored glycogen. As a result of the increased glycogen storage, the athlete will be able to generate more ATP and experience less fatigue during the completion of the high-intensity athletic event.

Carbohydrate loading is only necessary for moderate- to high-intensity endurance events that last more than 90 minutes. To achieve the desired results, both the loading of carbohydrate and the reduction in physical activity must occur. The most common mistakes made by athletes participating in carbohydrate loading can be attributed to not coupling it with an exercise taper, failing to eat enough carbohydrates, consuming too much fiber, fear of weight gain, and eating too many high fat foods.¹⁰ Also, since athletes are used to continuous training, they can find it difficult to cut back on training for 1-4 days. Some of the risks involved with carbohydrate loading are weight gain, blood sugar changes, and gastrointestinal issues. Therefore, athletes, especially those with diabetes, should consult with their physician and/or dietitian before engaging in carbohydrate loading. For most other athletes as long as their diet is 50% or more carbohydrates, they will not need carbohydrate loading and can participate and excel in athletic events.

Anemia

Hemoglobin is the protein in red blood cells that binds to oxygen from the lungs and delivers it to the rest of the body. Anemia is a condition that occurs when there is some malfunction in regards to a person’s hemoglobin—they don’t produce enough, their hemoglobin is ineffective in some aspect, or the body has lost it through bleeding. The result of all of these scenarios is that the body tissues do not receive enough oxygen. Although there are several types of anemia, iron deficiency anemia (IDA) occurs when there is a lack of iron that is essential for making hemoglobin. IDA is the most frequently occurring blood disorder worldwide, affecting more than 3 million Americans.¹¹ This form of anemia is often seen in athletes, particularly females.

IDA can range from mild to severe. Common signs and symptoms include fatigue, weakness, headache, difficulty concentrating, headache, shortness of breath, brittle nails or “spooning” of the nails, cracks at the side of the mouth and swelling or soreness of the tongue, pale skin, coldness in extremities, dizziness. In severe deficiency one can experience chest pain, irregular heart beat, or restless legs syndrome. Some people also experience pica which is an unusual craving for a nonfood item such as ice, dirt, paint, or starch.¹¹ The athletic performance of a person with anemia will be greatly impaired and anemia should be suspected in any athlete whose stamina has diminished or who is experiencing any of the other symptoms mentioned above.

Treatment includes encouraging the intake of iron-containing foods like beans and lentils, leafy vegetables, nuts, meats and tofu. Consumption of vitamin C containing foods such as fresh fruits can improve absorption of iron from other sources, especially when a person is deficient. IDA will be discussed in more detail in Chapter 16.

Female Athlete Triad (or Relative Energy Deficiency in Sport or RED-S Syndrome)

Athletes require intense training which can put extensive physical strain on the body. In some cases, athletes restrict dietary intake in an attempt to meet performance goals. Although this can be taxing on any athlete, many studies show there are specific health risks for female athletes competing at a high level. These athletes are at risk for a condition originally termed the “female athlete triad.” It is a combination of three interrelated conditions: disordered eating (RED-S), menstrual dysfunction, and osteopenia (loss of bone density; a precursor to osteoporosis). It usually begins when the athlete fails to consume adequate calories and/or nutrients. This leads to a loss of body fat. Women with low amounts of body fat also have lower amounts of a circulating hormone called estradiol (estrogen). When the levels of estradiol fall, menstrual cycles can become irregular or cease completely, and the bones lose density and become weakened (osteopenia). Male athletes who do not consume adequate kcal and nutrients can also experience osteopenia.¹² 

Athletes with this syndrome are at higher risk for injury and often athletic performance suffers greatly. They should be carefully monitored and treated for disordered eating when appropriate (see Chapter 10 for more information about disordered eating).

Fluids

Physical exercise increases the contraction of skeletal muscles. This action raises the body’s total metabolism to function at least five times the rate of an individual’s resting heart rate. The majority of this energy is given off by heat. In particularly warm environments, body fluids may be lost through sweat cooling off the body, therefore aiding in equilibrium.¹³

If exercise is frequent and intense, athletes need to be consuming appropriate liquids to compensate for the lost fluids. The lack of fluid intake can lead to dehydration. A 1-2% reduction in body weight indicates fluid losses that can reduce athletic performance, increase RPE, and lead to fatigue. Excessive losses of more than 5-10% of body weight can cause physiological effects that can be life-threatening such as large reductions in blood plasma volume leading to rapid pulse and, in extreme cases, cardiogenic shock.¹⁰ Not only does the overall performance of an athlete decline with dehydration, but post-exercise recovery suffers as well. When deprived of fluids, the body has to work harder to repair muscle tissues and remove bloodstream waste.¹⁴

How Dehydration Leads to Fatigue

Water is a great heat sponge. During exercise, as body temperature rises, the water in the blood absorbs this excess body heat. It then releases the heated water from the blood through the skin to dissipate this heat, a process called sweating. As the water is lost from the blood, blood volume decreases but the blood cells remain, causing the blood to “thicken,” having a higher viscosity. This lowered blood volume and higher viscosity reduces the rate and amount of blood the heart fills with between beats, called end diastolic volume (EDV). The body still needs high amounts of blood to circulate because exercise is still occurring, so heart rate increases to compensate for the lowered blood volume. Eventually the ability of the cardiovascular system to keep up with demand is impaired, and blood flow to working muscles declines. In addition, blood flow to the skin also decreases, resulting in a decrease in sweating. This diminishes the body’s ability to dissipate generated heat, so core body temperature rises, resulting in fatigue.

Heat-Related Illness

Dehydration can cause heat-related illness such as heat cramps, heat exhaustion, and heat stroke because there is less water in the blood to absorb the heat.. Table 11.4.1 provides descriptions of these illnesses.

Table 12.4.1 Heat-Related Illnesses

Electrolytes, along with water, are lost in sweat. Electrolytes are used to maintain fluid balance in the human body. They play a role in conducting electrical activity and are charged ions. Having a proper balance of electrolytes allows the body to not only regulate the balance of fluids, but muscle and neural activity as well. Sodium and chloride are the major electrolytes lost in sweat. Other electrolytes lost are calcium, potassium, and magnesium. The balance of these minerals lost via sweat varies with the individual.¹⁵

Because of the negative performance consequences associated with even mild dehydration and electrolyte loss, athletes must have a plan for hydration because thirst is not a precise mechanism for signaling fluid needs, especially in the very young and in older adults.¹⁰ You can reduce your risk of dehydration by becoming acclimated to exercise in the heat and humidity which improves your heat tolerance. Competing at high altitudes also increases water needs.

Consume adequate fluids before, during, and after exercise. One way to determine the amount of fluids you lose during an exercise bout is to weigh yourself before and after. For each pound (16 oz) lost you should replace it with 16-24 oz of fluids. While this technique works for water replacement, it should also provide some guidance about the amount of fluid you should consume during exercise so that you avoid the consequences of inadequate hydration.

For example, if you consistently lose 2.5 pounds during hour long runs in the heat, that’s a loss of 40 oz of fluid. Figure out a way to consume these 40 oz immediately before and during exercise, and you may find that your runs are faster and you feel less fatigue. You may try to consume 8 oz (1 cup) about 15 minutes before you begin, then additional consumption of 4 oz about every 10 minutes (every mile) throughout the run. Even if you cannot avoid net fluid loss during exercise, delaying the onset of fatigue by consuming at least some fluid during exercise will help.

Weight Management in Athletes

Sometimes weight loss or weight gain is recommended for an athlete to maximize performance. However, restricting calories during periods of high activity can lead to nutrient deficiencies, especially vitamin and mineral deficiencies. This negatively impacts athletic performance, and has adverse repercussions for general health and well-being. On the other hand, modifying dietary intake for weight gain during periods of high activity can also have negative consequences. Athletes who wish to lose or gain weight should do so during the off-season for their sport. It is highly recommended that they seek out the help of a registered dietitian specializing in sports dietetics so as not to jeopardize athletic performance or their overall health.

Athletes and Caffeine

Caffeine is a nervous system stimulant. Consumption of caffeine, usually in beverages, increases heart and breathing rates, and alertness. It improves reaction time and focus while reducing RPE and feelings of fatigue. Doses of 3-13 mg per kg body weight (generally 200-400 mg) have been shown to be the most beneficial. Benefits may be minimized in athletes who regularly consume caffeine. Intakes greater than 500 mg can lead to insomnia, restlessness, ringing of the ears, and a reduction in athletic performance.¹⁰ Furthermore, caffeine acts as a diuretic and may cause the need to urinate during competition, leading to fluid losses.⁹ Caffeine can also increase peristalsis in the intestines, leading to a need to defecate.

Conclusion

A comprehensive fitness program tailored to an individual typically focuses on one or more specific skills, and on age- or health-related needs such as bone health. Many sources also cite mental, social, and emotional health as an important part of overall fitness. Physical fitness can prevent or treat many chronic health conditions brought on by unhealthy lifestyle or aging. Working out can also help some people sleep better and possibly alleviate some mood disorders in certain individuals. It is crucial to maintain nutritious eating and fluid intake not only for athletic events, but all of the time. A pre-game meal or special diet for several days prior to competition cannot make up for inadequate nutrition in previous months or years. Lifelong nutrition habits must be emphasized. Combining good eating practices with a good training and conditioning program will allow any athlete to maximize their performance.

Portions of this chapter were taken from OER Sources listed below:

Tharalson, J. (2019). Nutri300:Nutrition. https://med.libretexts.org/Courses/Sacremento_City_College/SSC%3A_Nutri_300_(Tharalson)

Additional References:

1. United States Department of Health and Human Services. (2018). Physical activity guidelines for Americans (2nd ed.). https://health.gov/sites/default/files/2019-09/Physical_Activity_Guidelines_2nd_edition.pdf
2. Fundamentals of human nutrition. (2018, August 11). In Wikibooks. https://en.wikibooks.org/wiki/Fundamentals_of_Human_Nutrition
3. Sports Coach. (2020, February 5). Conditioning. Brian Mac Sports Coach. https://www.brianmac.co.uk/conditon.htm
4. Centers for Disease Control and Prevention. (2020, April 10). Target heart rate and maximum estimated heart rate. https://www.cdc.gov/physicalactivity/basics/measuring/heartrate.htm
5. Centers for Disease Control and Prevention. (2020, April 10). Measuring physical activity intensity. https://www.cdc.gov/physicalactivity/basics/measuring/index.html
6. Centers for Disease Control and Prevention. (2020, April 10). Perceived exertion (Borg Rating of perceived exertion). https://www.cdc.gov/physicalactivity/basics/measuring/exertion.htm
7. Ekelund, U., Steene-Johannessen, J., & Brown, W. J. (2016). Does physical activity attenuate, or even eliminate, the detrimental association of sitting time with mortality? A harmonized meta-analysis of data from more than 1 million men and women. Lancet, 388, 1302-1310.
8. Moore, S. C., Patel, A. V., & Matthews, C. E. (2012). Leisure time physical activity of moderate to vigorous intensity and mortality: A large pooled cohort analysis. PLoS Med, 9(11):e1001335. doi:10.1371/journal.pmed.1001335
9. Thomas, D. T., Erdman, K. A., & Burke, L. M. (2016). Position paper of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and athletic performance. Journal of the Academy of Nutrition and Dietetics, 116(3), 501-528.
10. Karpinski, C., & Rosenbloom C. A. (Eds.). (2017). Sports nutrition: A handbook for professionals (6th ed). Academy of Nutrition and Dietetics.
11. National Heart, Lung, and Blood Institute. (n.d.). Iron-deficiency anemia fact sheet. National Institutes of Health. https://www.nhlbi.nih.gov/health-topics/iron-deficiency-anemia
12. Statuta, SM, Asif, I. M., & Drezner, J. A. (2017). Relative energy deficiency in sport (RED-S). British Journal of Sports Medicine, 51, 1570-1571. http://dx.doi.org/10.1136/bjsports-2017-097700
13. Sawka, M. N., & Montain, S. J. (2000). Fluid and electrolyte supplementation for exercise heat stress. American Journal of Clinical Nutrition, 72(suppl), 564S-72S. http://ajcn.nutrition.org/content/72/2/564s.full.pdf
14. Fischer-Colbrie, M. (2017, July 21). Athletes, sweat, and why you need electrolytes. http://blog.bridgeathletic.com/athletes-sweat-and-why-you-need-electrolytes-bridgeathletic
15. Dolan, S. H. (n.d.). Electrolytes: Understanding replacement options. American Council on Education. https://www.acefitness.org/certifiednewsarticle/715/electrolytes-understanding-replacement-options/