Aerobic Exercise

Aerobic exercise refers to exercise that involves or improves oxygen consumption by the body. Aerobic means "with oxygen", and refers to the use of oxygen in the body's metabolic or energy-generating process.

A type of physical activity that includes walking, jogging, running, and dancing. Aerobic training improves the efficiency of the aerobic energy-producing systems that can improve cardiorespiratory endurance.

Aerobic activities include: walking, biking, jogging, swimming, aerobic classes and cross-country skiing. Anaerobic activity is short in duration and high in intensity.

Anaerobic activities include: racquetball, downhill skiing, weight lifting, sprinting, softball, soccer and football.

Aerobic means with air or oxygen. You should be able to carry on a short conversation while doing aerobic exercise. If you are gasping for air while talking, you are probably working anaerobically. When you work anaerobically, you will tire faster and are more likely to experience sore muscles after exercise is over.

Cardiovascular Benefits

Aerobic exercise conditions the heart and lungs by increasing the oxygen available to the body and by enabling the heart to use oxygen more efficiently. Exercise alone cannot prevent or cure heart disease. It is only one factor in a total program of risk reduction; examples of other factors are high blood pressure, cigarette smoking and high cholesterol level.

Additional Benefits of Aerobic Exercise

In addition to cardiovascular benefits, other benefits of aerobic exercise include:

• Control of body fat. (Aerobic exercise in conjunction with strength training and a proper diet will reduce body fat.)
• Increased resistance to fatigue and extra energy.
• Toned muscles and increased lean body mass.
• Decreased tension and aid in sleeping.
• Increased general stamina.
• Psychological benefits - exercise improves mood, reduces depression and anxiety.

Aerobic Classes (step, hi/low, slide, interval etc...)

In an aerobic class, you can do moves in low intensity or high intensity. The level of intensity depends upon how high you bring your arms (not whether the class is low impact or high impact). Aerobic instructors should show class members how to do moves in high or low intensity. Participants should choose their own level of intensity dependent upon their level of fitness and how frequently they exercise.

If you are too tired to continue exercising in an aerobic class, march in place for a while until you can resume exercising. IT IS NOT OK to stop in the middle of an aerobic class because your body is sending extra blood to the muscles. Stopping suddenly can lead to muscle cramping and dizziness (this is why all aerobic classes have a cool down at the end of the aerobic section).

What is aerobic exercise?

Imagine that you're exercising. You're working up a sweat, you're breathing hard, your heart is thumping, blood is coursing through your vessels to deliver oxygen to the muscles to keep you moving, and you sustain the activity for more than just a few minutes. That's aerobic exercise; any activity that you can sustain for more than just a few minutes while your heart, lungs, and muscles work overtime. In this article, I'll discuss the mechanisms of aerobic exercise; oxygen transport and consumption, the role of the heart and the muscles, the proven benefits of aerobic exercise, how much you need to do to reap the benefits, and more.

The beginning

It all starts with breathing. The average healthy adult inhales and exhales about 7 to 8 liters of air per minute. Once you fill your lungs, the oxygen in the air (air contains approximately 20% oxygen) is filtered through small branches of tubes (called bronchioles) until it reaches the alveoli. The alveoli are tiny sacs (they kind of look like bunches of grapes, and you have about 300,000,000 in each lung!) where oxygen diffuses (enters) into the blood. From there, it's a beeline direct to the heart.

Getting to the heart of it

The heart has four chambers that fill with blood and pump blood (two atria and two ventricles) and some very large and active coronary arteries. Because of all this action, the heart needs a fresh supply of oxygen, and as you just learned, the lungs provide it. Once the heart uses what it needs, it pumps the blood, the oxygen, and other nutrients out through the large left ventricle and through the circulatory system to all the organs, muscles, and tissue that need it.

A whole lot of pumping going on

Your heart beats approximately 60-80 times per minute at rest, 100,000 times a day, more than 30 million times per year, and about 2.5 billion times in a 70-year lifetime! Every beat of your heart sends a volume of blood (called stroke volume—more about that later), along with oxygen and many other life-sustaining nutrients, circulating through your body. The average healthy adult heart pumps about 5 liters of blood per minute.

Oxygen consumption and muscles

All that oxygen being pumped by the blood is important. You may be familiar with the term "oxygen consumption." In science, it's labeled VO2, or volume of oxygen consumed. It's the amount of oxygen the muscles extract, or consume from the blood, and it's expressed as ml/kg/minute (milliliters per kilogram of body weight). Muscles are like engines that run on fuel (just like an automobile that runs on fuel); only our muscles use fat and carbohydrates instead of gasoline. Oxygen is a key player because, once inside the muscle, it's used to burn fat and carbohydrate for fuel to keep our engines running. The more efficient our muscles are at consuming oxygen, the more fuel we can burn, the more fit we are, and the longer we can exercise.

How aerobically fit can we be?

The average sedentary adult will reach a level of oxygen consumption close to 35 ml/kg/min during a maximal treadmill test (where you're asked to walk as hard as you can). Translated, that means the person is consuming 35 milliliters of oxygen for every kilogram of body weight per minute. That'll get you through the day, but elite athletes can reach values as high as 90ml/kg/minute! How do they do it? Good genes for one, but they also train hard. And when they do, their bodies adapt. The good news is that the bodies of mere mortals like the rest of us adapt to training too. Here's how.

What are the fitness benefits of aerobic exercise?

How our bodies adapt

Here's what happens inside your body when you do aerobic exercise regularly:

1. Your heart gets stronger and pumps more blood with each beat (larger stroke volume). Elite athletes, as I just mentioned, can have stroke volumes more than twice as high as average individuals. But it's not just that. Conditioned hearts also have greater diameter and mass (the heart's a muscle too and gets bigger when you train it), and they pump efficiently enough to allow for greater filling time, which is a good thing because it means that more blood fills the chambers of the heart before they pump so that more blood gets pumped with each beat.

2. Greater stroke volume means the heart doesn't have to pump as fast to meet the demands of exercise. Fewer beats and more stroke volume mean greater efficiency. Think about a pump emptying water out of a flooded basement. The pump works better and lasts longer if it can pump larger volumes of water with each cycle than if it has to pump faster and strain and to get rid of the water. High stroke volume is why athletes' hearts don't pump as fast during exercise and why they have such low resting heart rates; sometimes as low as 40 beats per minute, whereas the average is 60-80 beats per minutes!

3. Downstream from the heart are your muscles, which get more efficient at consuming oxygen when you do regular aerobic exercise. This happens because of an increase in the activity and number of enzymes that transport oxygen into the muscle. Imagine 100 oxygen molecules circulating past a muscle. You're twice as fit if the muscle can consume all 100 molecules than if it can only consume 50. Another way of saying it is that you're twice as fit as someone if your VO2 max is 60ml/kg/min and theirs is 30ml/kg/min. In terms of performance in this scenario, you'll have more endurance because your muscles won't run out of oxygen as quickly.

4. Mitochondria inside the muscle increase in number and activity. Mitochondria are the powerhouses of your cells. They do all the heavy-duty work to keep you moving. They use the oxygen to burn the fat and carbohydrate that makes you go. You'd be nowhere without mitochondria! The good news is that they increase in number and activity, by as much as 50%, in just a matter of days to weeks in response to regular aerobic exercise in adults of all ages.

Burn, baby, burn

I mentioned that fat and carbohydrate are the fuels our muscles burn. The difference between them is that fat is high-test; it contains 9 calories per gram whereas carbohydrate has only 4, and so you get more energy and can go farther on a gram of fat than on a gram of carbohydrate. You want to burn fat because it's such an efficient fuel, plus it's nice to lose some of your excess fat! The catch is that you need more oxygen to burn fat because it's denser than carbohydrate. The good news is that your body gets better at using oxygen and burning fat when you do regular aerobic exercise; like I described, your heart pumps more blood, your muscles consume more oxygen, and you have more mitochondria. Regular aerobic exercise has the potential to turn you into a lean, mean, fat-burning machine!

What is the difference between aerobic and anaerobic exercise?

It's any activity that stimulates your heart rate and breathing to increase but not so much that you can't sustain the activity for more than a few minutes. Aerobic means "with oxygen," and anaerobic means "without oxygen." Anaerobic exercise is the type where you get out of breath in just a few moments, like when you lift weights, when you sprint, or when you climb a long flight of stairs (or a short flight if you're deconditioned!)

A caveat

Dancing, swimming, water aerobics, biking, walking, hiking, and many other activities are all examples of aerobic activities, but they can be anaerobic too if they are performed at a high enough intensity. Try riding your bike alongside Lance Armstrong in the French Alps and you'll know what anaerobic exercise means in moments. But then again, riding along on your bike at a leisurely 8-10 mph on the boardwalk at the seashore is the same activity, but at a much lower intensity, much lower heart rate, and much lower oxygen consumption, and so in this case, biking is aerobic. The bottom line is that the intensity that you perform an activity determines if it's aerobic or anaerobic.

What are the health benefits of aerobic exercise?

Perhaps no area of exercise science has been more studied than the benefits of aerobic exercise. There is a mountain of evidence to prove that regular aerobic exercise will improve your health, your fitness, and much more. Here's a partial list of the documented health benefits of aerobic exercise.

Obesity and weight control

Aerobic exercise is believed by many scientists to be the single best predictor of weight maintenance. You can lose weight without exercise by reducing your caloric intake enough so that you burn more calories than you consume, but it takes a regular dose of exercise to keep your weight off. How much is not clear, but somewhere between 40 minutes of vigorous exercise several times per week to 75 minutes of moderate intensity exercise five or more days per week is probably about right. Your mileage will vary, and so once you get to the weight that you want to be at you'll need to experiment with different amounts of exercise until you find the one that works for you.

The American College of Sports Medicine recommends that overweight and obese individuals progressively increase to a minimum of 150 minutes of moderate intensity physical activity per week, but for long-term weight loss, overweight and obese adults should eventually progress to 200 to 300 minutes per week of moderate-intensity physical activity.
Aerobic exercise definitely burns lots of calories. Below is a table of minutes of continuous activity necessary to expend 300 calories based on your body weight.

TABLE: Minutes of continuous activity necessary to expend 300 kcal based on body weight.

		Body weight (lb)
		120	130	140	150	160	170	180	190	200	210	220	230	240	250
Conditioning exercises
Cycling
	Stationary	66	61	57	53	50	47	44	42	40	38	36	35	33	32
	Outdoor (leisure)	83	76	71	66	62	58	55	52	50	47	45	43	41	40
Walking
	2.5 mph	110	102	94	88	83	78	73	70	66	63	60	58	55	53
	3.0 mph	94	87	81	76	71	67	63	60	57	54	52	49	47	45
	3.5 mph	83	76	71	66	62	58	55	52	50	47	45	43	41	40
Water aerobics		83	76	71	66	62	58	55	52	50	47	45	43	41	40
Lap swimming		41	38	35	33	31	29	28	26	25	24	23	22	21	20
Yoga		83	20	21	23	24	26	27	29	30	32	33	35	36	38
Resistance exercise		55	51	47	44	41	39	37	35	33	31	30	29	28	26
Dancing
Aerobic dance		55	51	47	44	41	39	37	35	33	31	30	29	28	26
Low-impact aerobic dance		66	61	57	53	50	47	44	42	40	38	36	35	33	32
Ballroom dance (fast)		60	56	52	48	45	42	40	38	36	34	33	31	30	29
Ballroom dance (slow)		110	102	94	88	83	78	73	70	66	63	60	58	55	53
Lifestyle activities
Golf (walking)		73	68	63	59	55	52	49	46	44	42	40	38	37	35
Raking the lawn		83	76	71	66	62	58	55	52	50	47	45	43	41	40
Lawn mowing
	Walking power mower	73	68	63	59	55	52	49	46	44	42	40	38	37	35
	Riding mower	132	122	113	106	99	93	88	84	79	76	72	69	66	63
Vacuuming/sweeping		132	122	113	106	99	93	88	84	79	76	72	69	66	63

Body mass index <18>2 is not recommended, and therefore these values have not been represented on this table.

How much aerobic exercise do you need to do to gain the benefits?

There are two physical activity guidelines in the Unites States. The first, the Surgeon General's Report on Physical Activity and Health, is a lifestyle recommendation. That is, you can modify it to fit into your daily routine and activities of daily living. The recommendation is that all adults should accumulate 30 minutes of moderate-intensity activity on most, if not all days of the week. The key words are "accumulate" and "moderate-intensity." Accumulate means that you can do 10-15 minutes at a time and repeat that a couple of times throughout the day; for example, 10 minutes in the morning, 10 minutes at lunch, and 10 minutes around dinner. Moderate intensity is equivalent to feeling "warm and slightly out of breath" when you do it.

The second recommendation is from the American College of Sports Medicine. The ACSM recommends 20-60 minutes of continuous aerobic activity (biking, walking, jogging, dancing, swimming, etc.), three to five times a week, at 60%-90% of maximum heart rate, and two to three days of resistance training. This is a more formal, "workout" recommendation, although you can also accumulate the more intense workout in bouts of 10-15 minutes throughout the day if you like.

Which one you choose is a personal choice. They are not intended to compete with each other, but rather provide options, and maybe even complement each other. For instance, the Surgeon General's recommendation may be more practical for individuals who are unwilling, or unable, to adopt the more formal ACSM recommendation. Of course, there's no downside to working out regularly with aerobic exercise and also becoming more physically active as per the Surgeon General (take more stairs, mow the lawn by hand, park far away from the store and walk).

How do I go about getting started with aerobic exercise?

My suggestion for getting started is almost always the same. Keep it simple, keep it practical, keep it convenient, keep it realistic, keep it specific, and don't try to make up for years of inactivity all at once. Select any activity and amount of time where the probability of sticking with it is high. You may not love walking, but if you can do it right outside your door, and it requires no special equipment, and you already know how to do it (you've been walking your entire life!), then walking might be your best bet for getting started because it's so convenient.

What I mean by "be specific" pertains to setting exercise plans. Planning is helpful for behavior change, and I suggest that you set goals each week. I suggest writing down what day(s) of the week you'll exercise, what time of day, minutes of activity, location, and the activity that you'll do. Be as specific and realistic as possible, and remember that it's not how much you do when you get started but that you simply get started (getting started is usually the hardest part).

A sample plan might look like this:

• Monday: Take a 20-minute brisk walk at 7 a.m. around the block four times.
• Tuesday: Do the same as on Monday.
• Wednesday: Take a 20-minute walk at 6:30 p.m. (right before dinner) around the block.
• Thursday: Take the day off.
• Friday: Take a 20-minute walk at 7 a.m. around the block.
• Saturday: Walk with your family at 10 a.m. for 45 minutes in park.
• Sunday: Bike ride with your spouse for 60 minutes in park at noon. Mom will baby-sit.

I suggest keeping records of your weekly progress by writing down what happens, or at least checking off that you followed through, and then setting your weekly plan every week for at least three months. Then at three months you can evaluate your progress and see if any changes need to be made.

Also ask yourself at that time if you believe you will be exercising regularly in six more months. If the answer is "I'm not sure," or "no," then you ought to continue to set weekly goals. If you are confident that you can maintain the behavior and will be exercising in six months, then you may not need to set weekly goals, but at the fist sign of slipping, you ought to go back to it.

What are some aerobic training workouts and routines?

There are a number of ways to approach aerobic training. I'll use walking as an aerobic activity and go through some of the training methods. You can plug in any other aerobic activity if you prefer. If you're interested in running, please read the Running article.

"Simple" aerobic training

The simplest method of starting is just that, simple. Select the number of minutes you'd like to walk for (let's say 20 minutes for your first walk) and head out the door or step on the treadmill and go for it. Remember that to make it aerobic you want to walk at a pace that leaves you feeling "warm and slightly out of breath" and one that you can sustain for the time that you planned. In this case, set your sights on completing 20 minutes and pace yourself to do it. If you start too quickly, then you may poop out too soon. It's not important how fast you do it; it's just important that you attempt to complete the time. If you find 20 minutes is too ambitious, then start with less. Again, the most important thing is to get started. You can always add more later on.

Five-out, five-back training plan

Borrowing from Mark Fenton, I like the simplicity of the five-minute out, five-minute back aerobic training plan. Just like it sounds, you walk or jog out for five minutes, stop, and return to your starting place. That's it. 10 minutes and off you go about your day! If you feel ambitious you can try seven and a half out and seven and a half back, or even 10 out and 10 back. People frequently report that this isn't enough, but remember, the point is to get started; you can always add more later on.

Interval training

Interval training is more intense than simple aerobic training. It's a very effective way to increase your fitness level (remember stroke volume and mitochondria activity!), but it's tough, and so I recommend holding off until you build up to 20-30 minutes of aerobic exercise. The idea to intervals is to set up work to active-rest ratios (work:active-rest), and as you get more fit, decrease the active-rest interval and increase the work interval. The work interval of the ratio is a speed that is faster than what you usually do, and the active-rest interval is your usual speed. To do it, you start at your usual speed for five to eight minutes, then increase the speed to the work interval for one to three minutes, then slow down to your usual speed for a few minutes to catch your breath (this is the active-rest interval), and then you repeat the cycling for the duration of your workout.

Here are some examples of interval training using walking as the activity:

Training Plan #1

Try the following if you currently walk for 30 minutes at 3.5 mph on the treadmillInterval 1: 3.5 mph for five minutes to warm upInterval 2: 3.8 mph for one minuteInterval 3: 3.5 mph for three minutes to catch your breath (active-rest)Interval 4: 3.8 mph for one minuteInterval 5: 3.5 mph for three more minutes, and so on until you reach 30 minutes.
After a few weeks you can try increasing using plan #2.

Training Plan #2

The work:active-rest ratio in the above example is 1:3. Over the course of weeks and months, you increase the work interval and decrease the active-rest. For example:Interval 1: 3.5 mph for five minutes to warm upInterval 2: 3.8 mph for two minutesInterval 3: 3.5 mph for two minutes (active-rest)Interval 4: 3.8 mph for two minutesInterval 5: 3.5 mph for two more minutes, and so on until you reach 30 minutes.

Training Plan #3

The work:active-rest ratio in the above example is 1:3. Over the course of weeks and months you increase the work interval and decrease the active-rest. For example:Interval 1: 3.5 mph for five minutes to warm upInterval 2: 3.8 mph for three minutesInterval 3: 3.5 mph for one minutes (active-rest)Interval 4: 3.8 mph for three minutesInterval 5: 3.5 mph for one more minute, and so on until you reach 30 minutes.

As you can see, the ratio changed from 1:3 to 3:1 (work to active-rest). The next step would be to do all four minutes at 3.8 mph (the new active-rest) and increase the work interval for one minute to 4.0 mph.

One final note.

Spin class is interval training. It's done at gyms on special spin cycles with an instructor who barks out orders to increase the intensity and then slow down to catch your breath. It's addictive, and people who do it regularly swear by it. You should already be doing some aerobic exercise and be reasonably conditioned before you try it, but I recommend it if you're looking for one of the toughest workouts around.

Heart rate training

You can get more specific with your aerobic interval training and use heart rate since it's an excellent indication of how hard you are working. Let's use jogging on a treadmill as the aerobic activity in this example. For example, if your heart rate is at 70% of your predicted maximum when you jog at 6 mph, then start at that speed and either increase the speed or elevation so that your heart rate increases to 85% or even 90% for one minute, then back to your usual jogging speed for three minutes to elicit a heart rate of 70%. Start with a 1:3 work:active-rest ratio. That's a good starting point, and as you increase the work intervals and decrease the active-rest ratios like in the examples above, you'll notice that your conditioning improves so that your heart rate will be lower at the higher speeds.

It's a good idea to plan your intervals in advance. Write them down so that you don't have to think about it while you're working out. I also suggest intervals no more than one to two times per week because they are tough workouts and you will need some time to recover. It's okay to do aerobic activity on days in between your intervals, but give your body a chance to recover from the intervals before doing them again.

Increasing duration and intensity

The general rule for increasing aerobic activity is 10% per week. Interestingly, there's no evidence to suggest that a 10% increase is the safest and most effective amount of time to increase, but that's the rule of thumb and it seems to work pretty well. So, if you're walking for 20 minutes then the next increase ought to be two minutes for the following week. The bottom line though is to listen to your body. If you find that increasing by 10% is very easy, then go ahead and try a little more. But if you find that you are tired for hours after your workout, or chronically sore or achy from your workouts, then you know you need to cut back to 10% increases. Learn how to listen to your body and everything should be okay.

What are the different types of aerobics classes?

Step, funk-fusion, hip-hop, jazz, kick box, boot camp, cardio box...There are dozens of classes to choose from. They last anywhere from 30-60 minutes and vary in intensity. Here's some advice for choosing classes:

1. Classes are generally rated as beginner, intermediate, and advanced. Choose the level that fits your condition. It's no fun taking an advanced class if you're a beginner. It will be hard and frustrating and you won't enjoy the experience. Watch the class or speak with the instructor to help you decide what's right for you. Sometimes it comes down to the class time that fits your schedule, but just be sure to not get in too far over your head.

2. Low-impact classes mean that one foot always stays on the ground. They are less intense than high-impact and may be more suitable if you are a beginner. Some classes are now called, "high-low" or "mixed-impact" which means they combine low and high-impact moves. Again, speak with the instructor if you're not sure.

3. High-impact means both feet leave the ground, so there will be jumping and balance moves. Stick with lower-impact and more gentle and rhythmic dance classes if you are concerned about the pounding (low back problems, knee arthritis, or other joint injuries).

4. Experiment until you find the classes that work best for you.

Classes are great for people who like to exercise with others, who like to dance, who like music and rhythm, who want the extra motivation and energy that an instructor and class provides, and who prefer the structure and schedule of a regular class. Classes, equipment, and videos are all great ways to stay fit and healthy, but if you're limited by injury or other conditions, then aerobic exercise chair workouts may be just the thing (see resources for online vendors). The instructor leads you through a workout in a chair and it's great exercise.

You might not need chair exercise, but you may have a parent or friend who does. Exercise videos and DVDs make great gifts!

The bottom line to equipment, classes, and videos is that if they get your heart rate elevated and keep it there, then it's aerobic and it counts!

Benefits of aerobic exercise

There are numerous benefits for health and general well being to be gained from regular cardiovascular exercise:

• Increased energy levels
• Reduced stress and improved mental health (due to the release of endorphins in the brain)
• Increased heart and lung efficiency
• Reduced blood pressure, resting heart rate and risk of stroke or heart attack.

Does aerobic exercise aid weight loss?

Weight is lost by creating a calorie deficit, burning more calories than you take in, so undertaking activities that burn large amounts of calories is an excellent accompaniment to a calorie controlled diet to help shift those unwanted pounds.

For example, half an hour of low paced jogging can burn around 300 calories. This can make a substantial contribution towards achieving the necessary calorie deficit to lose weight, or alternatively it can earn you a bar of chocolate that you feel less guilty about eating.

Aerobic exercises: At home

It is not essential to join a gym or to go out in the middle of winter to get an aerobic workout. There are a number of exercises that you can do in the privacy of your own home.
The cheapest options being putting on your favourite CD and dancing around the living room or giving the house a vigorous clean.

There is also an ever increasing array of affordable home fitness products available, such as steps, skipping ropes (remember to put your breakables a safe distance away), rebounders (rebounding is considered by NASA to be the “most efficient and effective exercise yet devised by man”), dance mats that you can use with your games console and exercise videos so that you can workout with your favourite celebrity.

Aerobic exercises: Outdoors

Even taking a few extra brisk walks can be enough to improve fitness and receive the benefits of aerobic exercise, just as long as you are working hard enough that your heart rate is increased and you are breathing faster.

Running, jogging or going out for a bike ride when the weather’s nice are all good forms of aerobic exercise.Pretty much any exercise is better than no exercise at all, however, team sports are often less effective for developing aerobic fitness as while they involve periods where large amounts of energy is expended, these are often surrounded by periods of activity where the heart rate is allowed to drop.

The real benefits of aerobic exercise come from constant movement.

Aerobic exercises: Down the gym

Your local gym will provide a wide variety of aerobic options, such as treadmills, cross trainers, exercise bikes, stairmasters, rowing and ski machines so that you can just switch on and get started with your workout. It can be a good idea to diversify between different machines and different speeds/levels of resistance as your body can get used to a certain routine and after a number of sessions the same routine will not work your heart and lungs as much as it once did.

For those who prefer to work out as part of a group, many gyms provide classes, such as various forms of dance, body pump, body combat and step aerobics with a trained instructor to ensure that you get the most out of your workout.

If you have access to a pool, swimming is also a very effective cardiovascular activity. As it is very low impact it is often suitable for people who have had injuries or problems with muscles or joints.
How often to train

For good cardiovascular fitness it is generally recommended to exercise 3 to 5 times a week and for 30-60 minutes, not including warming up at the start and cooling down at the end.
The main thing is to ensure that your heart and lungs are worked hard enough and for long enough to gain the benefits of aerobic exercise but not so long that you run the risk of injury. To check whether you are working out at the correct intensity, you should be out of breath but still capable of speaking.

It is important to start slowly. If you have been inactive for some time, don’t throw on your trainers and set off on a ten mile run.

If a half an hour session feels like too much, start with 10 minute sessions for the first week then increase that to 15 or 20 minute sessions the next week and so on until you feel comfortable exercising for longer.

Make sure that you listen to your body. It’s ok for muscles to be tired, but if they or your joints start to feel sore or breathing becomes uncomfortable slow down or stop to ensure that you are in a fit state for your next session.

Aerobic versus anaerobic exercise

Aerobic exercise and fitness can be contrasted with anaerobic exercise, of which strength training and weight training are the most salient examples. The two types of exercise differ by the duration and intensity of muscular contractions involved, as well as by how energy is generated within the muscle. Initially during aerobic exercise, glycogen is broken down to produce glucose, which is then broken down using oxygen to generate energy. In the absence of these carbohydrates, fat metabolism is initiated instead. The latter is a slow process, and is accompanied by a decline in performance level. This gradual switch to fat as fuel is a major cause of what marathon runners call "hitting the wall". Anaerobic exercise, in contrast, refers to the initial phase of exercise, or to any short burst of intense exertion, in which the glycogen or sugar is consumed without oxygen, and is a far less efficient process. Operating anaerobically, an untrained 400 meter sprinter may "hit the wall" short of the full distance.

Aerobic exercise comprises innumerable forms. In general, it is performed at a moderate level of intensity over a relatively long period of time. For example, running a long distance at a moderate pace is an aerobic exercise, but sprinting is not. Playing singles tennis, with near-continuous motion, is generally considered aerobic activity, while golf or two person team tennis, with brief bursts of activity punctuated by more frequent breaks, may not be predominantly aerobic. Some sports are thus inherently "aerobic", while other aerobic exercises, such as fartlek training or aerobic dance classes, are designed specifically to improve aerobic capacity and fitness.

Among the recognized benefits of doing regular aerobic exercise are:

• Strengthening the muscles involved in respiration, to facilitate the flow of air in and out of the lungs
• Strengthening and enlarging the heart muscle, to improve its pumping efficiency and reduce the resting heart rate, known as aerobic conditioning
• Toning muscles throughout the body
• Improving circulation efficiency and reducing blood pressure
• Increasing the total number of red blood cells in the body, facilitating transport of oxygen
• Improved mental health, including reducing stress and lowering the incidence of depression

As a result, aerobic exercise can reduce the risk of death due to cardiovascular problems. In addition, high-impact aerobic activities (such as jogging or jumping rope) can stimulate bone growth, as well as reducing the risk of osteoporosis for both men and women. In addition to the health benefits of aerobic exercise, there are numerous performance benefits:

• Increased storage of energy molecules such as fats and carbohydrates within the muscles, allowing for increased endurance
• Neovascularization of the muscle sarcomeres to increase blood flow through the muscles
• Increasing speed at which aerobic metabolism is activated within muscles, allowing a greater portion of energy for intense exercise to be generated aerobically
• Improving the ability of muscles to use fats during exercise, preserving intramuscular glycogen
• Enhancing the speed at which muscles recover from high intensity exercise

"Aerobics" is a particular form of aerobic exercise. Aerobics classes generally involve rapid stepping patterns, performed to music with cues provided by an instructor. This type of aerobic activity became quite popular in the United States after the 1970 publication of The New Aerobics by Dr. Kenneth H. Cooper, and went through a brief period of intense popularity in the 1980s, when many celebrities (such as Jane Fonda and Richard Simmons) produced videos or created television shows promoting this type of aerobic exercise. Group exercise aerobics can be divided into two major types: freestyle aerobics and pre-choreographed aerobics.

Varieties of Aerobic Exercise

Indoor

• stair climbing
• elliptical trainer
• indoor rower
• stairmaster
• stationary bicycle
• treadmill
  

Outdoor

• crosscountry skiing
• cycling
• inline skating
• jogging
• nordic walking

Indoor or outdoor

• kickboxing
• swimming