A person's total daily caloric output is the sum total of the energy required in resting metabolism, thermal effect of food, and the calories burned during physical activity. Let's look at each of these factors and how it relates to weight loss.

Physical activity can have the most profound effect on caloric output. On average, physical activity accounts for 15-30 percent of total caloric output. Most of us can generate substantial increases in metabolism (up to 10 times the resting value), during sustained exercise such as
running and cycling. Bottom line: the more physically active the person, the more active their metabolism.

How can I tell if exercise is too intense or vigorous?
There are two ways to determine how intense you are exercising. One is the target heart rate method and the other is the Perceived Exertion Scale. While target heart rate is a measure of exercise intensity based on your pulse, the Perceived Exertion Scale is a subjective measure
based on how you feel. The target heart rate method is commonly used to measure exercise intensity, and relies on checking heart rate (called pulse). Target heart rate is defined as 65-80 percent of your maximum heart rate. This will provide the desired effect of aerobic fitness and fat burning by exercising in this training zone during exercise. Many people make the mistake of believing that aerobic fitness is achieved by raising heart rate. This is not true. Aerobic fitness is achieved by increased oxygen consumption over time, but heart rate is a convenient indicator of oxygen consumption.

If your average summer day is 89 degrees and 90 percent humidity by 9:00 am, then you have probably said "It's too hot" a few times. Hot weather can be very risky, even life-threatening if safety precautions are not followed. Dehydration and heat stroke are the main concerns.
Proper fluid intake is essential. Don't wait until you are dehydrated to increase your fluids. In addition to being well hydrated before you head out, you'll need 1/2 cup water replacement every 15 minutes.
Wear loose fitting, comfortable fabrics that are breathable such as cotton, and avoid dark colors. Wear only one layer of clothing such as a T-shirt and shorts. Exercising in a plastic suit is dangerous, as they cause profuse sweating and loss of vital fluid, and prevent necessary
cooling of the body.

Avoid exercising in the middle of the day when temperatures are the hottest. Plan your exercise in the early morning or evening. Pay attention to the various flags, black and red, which are flown to indicate heat index and to control physical activity. These flags indicate the
wet bulb globe temperature (WBGT) which is an index of a combination of readings from three temperatures: dry, humid, and radiant heat. These three temperatures in combination provide a more accurate reading of heat stress intensity.

Staying motivated
Some people say it is hard staying motivated to keep exercising. One problem that we see is boredom doing the same exercise over and over on a daily basis.

When it comes to exercise, variety is the key. Athletes call it cross-training. You may think, "but I'm not an athlete, how can I cross-train?" Cross-training is simply varying your routine to work different muscle groups as well as maintaining variety. For instance, running and cycling use the same muscles in different ways.

Being outdoors is a great way to vary your routine; jog or bike a different route. Top athletes vary their routines often to prevent the boredom that comes with repetition.

Scientists would define metabolism as the chemical reactions that make the energy in foods available to the various physiological systems of the body. For instance, energy is required for muscular activity, the growth of skin, hair, nails, maintenance of body temperature, and even absorption of food from the intestinal tract. A way to measure the rate of metabolism is to measure the rate at which oxygen is utilized by the body. This is called basal metabolic rate, or simply BMR (the terms basal metabolic rate and resting metabolic rate are used interchangeably). It acts as "the body's thermostat," much like the thermostat in your house. Resting metabolic rate accounts for approximately 60-75 percent of daily caloric output.

Also affecting resting metabolism is the influence of body size. BMR is proportional to the surface area of the body, in that larger individuals burn more calories than smaller individuals for similar activities. Differences in body composition also affect BMR. Fat tissue is
metabolically less active than muscle or lean body mass. Athletes with greater muscle development show a greater increase in metabolism over the non-athletic individual. Muscle accounts for approximately 20 percent of resting metabolism. Women, who have more fat in
proportion to muscle than men, have metabolic rates 5-10 percent lower than men of the same weight and height. When based on the same amount of lean body mass, metabolic rates for men and women are similar. The same phenomenon is observed with aging. In general, as people age, lean body mass decreases with increases in fat-mass. A 2 percent decrease in BMR with every 10 years of life is usually observed through adulthood.

Putting this information together, we can conclude that in the overweight person, there is too much body fat and not enough lean muscle mass. How do we change the ratio of fat to muscle? Some people believe that we can turn fat into muscle and vice versa. This is not true. Muscle tissue is made up of long protein-like fibers, whereas fat tissue is round receptacles designed to store fat. Excess calories in the diet causes fat cells to grow in size as they store more fat. Conversely, fat cells shrink when you burn more calories than you eat. Muscle fibers increase when worked (hypertrophy), and muscle fibers decrease when not used (atrophy).

An increase in metabolic rate is stimulated by eating due to the energy-requiring process of digesting, absorbing, and metabolizing the various nutrients. This accounts for approximately 10 percent of total caloric output. This process is sometimes referred to as the "specific
dynamic action" or "dietary-induced thermo genesis." It reaches a maximum within 1 hour after a meal. Therefore, skipping meals tends to decrease metabolic rate so you burn calories at a lower rate (in other words, you lower your thermostat). Not eating enough can be as bad as eating too much!

Strength training
What exactly is strength training? Some people call it weight lifting. Strength training is based on the principle that muscles adapt to the stress or resistance placed upon them. Why are we discussing this here with weight loss? Strength training can significantly increase your progress with fat reduction in one simple concept: More muscle = higher resting metabolism! Strength training can be accomplished a couple of ways:
        1. Using your body as weight resistance (sit-ups, push-ups)
        2. Use weight machines or free weights in a gym
For the person who is new to strength training, start out with exercises that use your body weight as resistance, or begin with some of the resistance machines available at your MWR gym. Beginning a strength training program using free weights may increase the risk of injury,
unless certified trainers and careful supervision is available. A program using resistance machines (such as Nautilus or Life Fitness), 2-3 times per week for 20-30 minutes is a nice addition to a PT program designed for fat loss and toning.

The exercise log
The exercise log is an important tool for you to keep track of your progress (it is very hard on a Friday to remember what you did on Monday!). The goal for frequency of exercise is no less than 3 times per week, but research shows better results with 5 days of week of exercise with 40-45 minutes duration, and strength training 2-3 sessions per week.

BARRIERS TO EXERCISE
"I don't have the time"
The most common excuse for not exercising regularly is no time. Most people tend to find time for the things they enjoy. Does your work, family, travel, etc. prevent you from keeping up your exercise goals? This is when we need to work in small amounts of exercise wherever
we can. Although we have stressed that 40-45 minutes of aerobic activity is optimal for weight loss, other small bursts of physical activity add up and are relevant. They are not meant to replace cardiovascular conditioning, but do help by using calories.

What does this tell us? It tells us that we can develop better habits in our lives to include "movement" in a society where everything we use is automated. How many times do you drive around the parking lot looking for that close space? Why not walk a little further? Do you live
a few miles from work? How about riding a bike on good weather days? Think about ways to sneak exercise into your daily routine.

Don't let yourself be talked into common excuses. If these sound familiar to you, think about resolving your relationship with exercise. How important is it in your life? Why are you exercising? What to expect exercise to do for you? What motivates you to exercise?

Most of us live in variable climates which often makes it difficult to keep up our exercise routine. Trying to go out for your daily jog with overcast skies and temperatures in the low 30's can de-motivate even the most faithful runner. Keep in mind that you wouldn't avoid building a snowman, sledding, or snow skiing just because it was cold outside. You would just dress appropriately. The same holds true for exercise in cold weather.

The most important thing to exercising in the cold is proper cold weather attire. A rule of thumb is one light layer of clothing for every 10-15 degrees below 70. Fabrics such as polypropylene absorb moisture while keeping you warm and dry. Cotton, on the other hand, gets wet and stays wet with perspiration. Polypropylene is best worn next to the skin under a waterproof, windproof outer layer such as Goretex. If waterproof attire is not needed, a fabric such as fleece provides warmth without weight. A hat is essential in cold weather as heat is
rapidly lost from the head. Gloves or mittens made of wool, fleece, or polypropylene are also a necessity in cold temperatures.

After you are suited up and ready to head out, what if you still don't feel like it? (as mentioned earlier, cold dreary weather can be a demotivator). Consider exercising with a friend or shipmate. A buddy system can help in cold weather.

Carbohydrate
Glucose is the end product of carbohydrate digestion. The metabolism of glucose produces energy for the body. Glucose that is not needed for energy is stored in the form of glycogen; a source of potential energy that is readily available when needed. Most glycogen is stored in the
liver and muscle cells. When these cells are saturated with glycogen, the excess glucose is converted into fat and is stored as fat tissue.

The utilization of glucose for energy is a complex system. For our purposes, we will focus on anaerobic and aerobic metabolism. Anaerobic means in the absence of oxygen. This energy system breaks down glucose for energy mainly during high intensity exercise that lasts between 10 to 90 seconds (400 meter run, 100 meter swim, longer sprint, wrestling, weight lifting, fencing).

During aerobic metabolism, both glucose and fat can be broken down in the presence of oxygen. This will predominate during exercise lasting longer than 2 minutes. Longer duration exercise promotes increased use of fat (jogging, running, brisk walking, cross-country skiing, biking).

We are always utilizing some combination of carbohydrate and fat, both at work and during exercise. The major determinants of what proportion of fat vs. carbohydrate we use are:
     1. availability of carbohydrate (limited supply) and fat (virtually unlimited!)
     2. intensity of exercise
     3. duration of exercise
     4. cardiovascular fitness level (Fit people are better at using fat as a source of fuel. Also, exercise has a glycogen sparing effect. The more we exercise, the more we tend to switch over to using fat for fuel rather than our glycogen stores).

Fat
During light and moderate exercise, a combination of fat and glucose is used for energy. Fat utilization increases over time with more fat being burned after 30 minutes of exercise. This is an important point. To burn fat, you need to do moderate exercise in periods of 30 minutes or greater.

Protein
Very little protein is used as an energy source during exercise. Protein may be used as an energy source if a person is dieting too severely. When you restrict calorie intake to lose weight, the body senses starvation and begins a "survival" reaction. Part of the process will
take a body protein (like muscle tissue), break it down and turn it into glucose in the liver. Strict dieting therefore, can lead to a loss of lean muscle tissue, not just fat loss. This is why starvation diets don't work. The only way to avoid this is to restrict calories moderately.

On the flip side of this, excess protein in the diet can be converted to sugar and then stored as fat. Many bodybuilders make this mistake by consuming excess protein in the form of protein powders and supplements, thinking they need protein to build muscle (protein supplements can lead to kidney damage if taken in large quantities). Only working a muscle with weights will cause a muscle to grow!

Types of exercise:
       1. Aerobic exercise
       2. Strength training
Aerobic exercise is any activity which requires large amounts of oxygen, uses large muscle groups, is rhythmic, and can be sustained over time. It increases the body's demand for oxygen, thereby adding to the workload of the heart and lungs which increases the heart rate. It strengthens the cardiovascular system and allows the body to burn fat for energy.

Examples of aerobic exercise are running, jogging, walking, swimming, cycling, cross-country skiing, rowing, and aerobic dance. Regardless of what you choose to do, the frequency and duration are most important. For fitness, the experts recommend aerobic activity a minimum of three times per week. If weight loss is your goal, you should to do it five times per week. Duration needs to be at least 30 minutes in duration, but for optimal fat loss, 40-45 minutes of exercise is more effective.