- What Is
- Aerobic vs. Anaerobic Exercise
- Calories Burned
- Home Program
- Heart Rate
- Disease Prevention
Aerobic exercise facts
- Aerobic exercise is sometimes known as "cardio" -- exercise that requires pumping of oxygenated blood by the heart to deliver oxygen to working muscles.
- Aerobic exercise stimulates the heart rate and breathing rate to increase in a way that can be sustained for the exercise session. In contrast, anaerobic ("without oxygen") exercise is activity that causes you to be quickly out of breath, like sprinting or lifting a heavy weight.
- Examples of aerobic exercises include cardio machines, spinning, running, swimming, walking, hiking, aerobics classes, dancing, cross country skiing, and kickboxing. There are many other types.
- Aerobic exercises can become anaerobic exercises if performed at a level of intensity that is too high.
- Aerobic exercise not only improves fitness; it also has known benefits for both physical and emotional health.
- Aerobic exercise can help prevent or reduce the chance of developing some cancers, diabetes, depression, cardiovascular disease, and osteoporosis.
- An aerobic exercise plan should be simple, practical, and realistic. Specific equipment (such as cardio machines) may be used but is not necessary for successful aerobic exercise.
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 (also known as "cardio" in gym lingo), which is 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.
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 microscopic sacs 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 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 (cardiovascular system) to all the organs, muscles, and tissues 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.
Why do you need aerobic exercise?
The average sedentary adult will reach a level of oxygen consumption close to 35 ml/kg/minute 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 90 ml/kg/minute! How do they do it? They may have 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 benefits of aerobic exercise?
How our bodies adapt
Here's what happens inside your body when you do aerobic exercise regularly:
- 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.
- 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 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.
- Downstream from the heart are your muscles, which get more efficient at consuming oxygen when you do regular aerobic exercise (remember, "consuming" oxygen means that the muscles are taking the oxygen out of the blood). This happens because of an increase in the activity and number of enzymes that transport oxygen out of the bloodstream and 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.
- 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. 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.
How much aerobic exercise do you need 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. Recently there has been some controversy about the effectiveness of this guideline and its benefits. At the moment the recommendation stands, but we may hear more about it in the not-too-distant future.
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. Follow this recommendation and your aerobic fitness and your health will improve.
Which one you choose is a personal choice. They are not intended to compete with each other but rather to 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), so combining them might be a good decision.
What is the difference between aerobic and anaerobic exercise?
I defined aerobic exercise for you in the introduction. 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 for improving strength, when you sprint, or when you climb a long flight of stairs.
Dancing, swimming, water aerobics, biking, walking, hiking, climbing steps (two at a time for a more vigorous workout), low-impact dance classes, kick-boxing, all the cardio machines at the gum (treadmill, elliptical, bike, rower, x-c skiing, stair-climber), and many other activities are all examples of types of aerobic or cardio 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 at which you perform an activity determines if it's aerobic or anaerobic.
How many calories do you burn with different types of aerobic exercise?
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
|Exercise type||Body weight (lbs.)|
|Minutes of exercise|
|Walking (2.5 mph)||110||102||94||88||83||78||73||70||66||63||60||58||55||53|
|Walking (3 mph)||94||87||81||76||71||67||63||60||57||54||52||49||47||45|
|Walking (3.5 mph)||83||76||71||66||62||58||55||52||50||47||45||43||41||40|
What is an example of a daily home aerobic exercise program?
My suggestion for getting started with an exercise program 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.
Another plan I like is the five-minute out, five-minute back plan. Just like it sounds, you walk for five minutes from your starting point, turn around, and walk back. It's simple and doable for almost everyone. It's a change in your activity behavior even though it's not all that much, and you can increase as you get more used to it. From five minutes you could go to seven and a half out, seven and a half back, a total of 15 minutes just like that. And you can keep your eye on 15 out, 15 back, and there you go meeting the Surgeon General's recommendation of 30 minutes. If you're feeling ambitious, you can add some abdominal crunches and push-ups once you get back. For push-ups, if you can't do a standard one on the floor, modify them by leaning against a wall, leaning against a table, or on your knees on the floor. The lower you go the harder they are. Start with two to three sets of crunches and push-ups, 12-15 repetitions, three to four days a week. As they get easier, you can increase the intensity of crunches by going slower or putting your legs in the air with your knees bent. As push-ups get easier, you can go to the next lower level (for example, from wall to table to on your knees on the floor).
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. How will you know if you're ready to stop setting weekly goals each week? Ask yourself if you believe you will be exercising regularly in six 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 first sign of slipping, you ought to go back to it.
How do you calculate your target heart rate during aerobic exercise?
Heart rate reserve
Your heart rate rises during aerobic exercise. It can rise from 70 beats per minutes (bpm) at rest to as high as 170 bpm or even higher during exercise, depending on the intensity of the exercise, your fitness level, your age, and other factors. Whether you're training is aerobic or anaerobic is determined by the intensity of your workout, and monitoring the intensity is the key to know which one you're doing.
For many individuals, simply monitoring how the body feels while exercising is enough to determine the proper aerobic intensity. I recommend "warm and slightly out of breath" as the cue for aerobic activity; that is if you feel warm and slightly out of breath while you're exercising, then that's good enough.
On the other hand, some people like to know with more precision how their body is doing during exercise. If that's the case for you, then taking your heart rate during exercise and using a target heart rate training zone might be just the ticket. Target heart rate zones range anywhere from 50% to 100% of your maximum heart rate (your maximum heart rate is based on your age). Aerobic exercise is anything less than 85%, and anaerobic exercise is anything above that. A nice starting point for a sedentary individual is somewhere in the range from 50% to 65% (you can always increase as you get more fit) and 65% to 85% for more conditioned individuals.
I recommend the heart-rate reserve method for calculating a target heart rate. Here's the formula and an example of the method for someone 27 years of age, assuming a resting heart rate of 70 bpm, and a training range of 70%. If you plug in other values, you can get other ranges.
- 220-age = Max HR.
- Subtract resting heart rate from Max HR = Heart Rate Reserve (HRR).
- Multiply HRR times percent you want to train at.
- Add back resting heart rate.
- Assuming a resting heart rate of 70 bpm, 27 years old, and 70% training range:
220 - 27 = 193
193 - 70 = 123
123 x .70% = 86
86 + 70 = 156
Please note: There's been some recent research to suggest a new way of estimating maximum heart rate. The formula is the following:
- Multiply 0.7 times your age.
- Subtract that number from 208.
An example if you're 26 years old is: 0.7 x 26 = 18, then 208 - 18 = 190. You'd then take 190 and plug it in as usual to the formula above. This new formula makes a slightly bigger difference as you get older.
You can read a complete review of heart rate training zones.
What are examples of the types of aerobic exercises?
There are a number of ways to approach aerobic training. I'll use walking as an example of an aerobic activity and go through some of the training methods. You can plug in any other aerobic activity if you prefer, such as running.
"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
As discussed above, I like the simplicity of the five-minute out, five-minute back aerobic training plan. And like I said, you can increase gradually to 15 minutes out, 15 minutes back. It's aerobic and you'll get a training effect as long as you feel warm and slightly out of breath when you do it.
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 treadmill.
Interval 1: 3.5 mph for five minutes to warm up
Interval 2: 3.8 mph for one minute
Interval 3: 3.5 mph for three minutes to catch your breath (active-rest)
Interval 4: 3.8 mph for one minute
Interval 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 up
Interval 2: 3.8 mph for two minutes
Interval 3: 3.5 mph for two minutes (active-rest)
Interval 4: 3.8 mph for two minutes
Interval 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 up
Interval 2: 3.8 mph for three minutes
Interval 3: 3.5 mph for one minutes (active-rest)
Interval 4: 3.8 mph for three minutes
Interval 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 OK.
List of examples of home and gym aerobic workout routines
The activity you choose is a personal choice and it varies for everyone, and so you need to experiment until you find what works best for you.
- Rowers, treadmills, bikes, and cross-country skiers are all effective if you use them.
- There is some suggestion that some individuals are more inclined to exercise at home with equipment than at the gym or a class.
- Some individuals prefer to go to the gym while others are perfectly content to work out at home on their own equipment in front of their TV. TV can make the time pass quickly, and so can your favorite movie, music, scholarly courses taught by professors, or books on tape (see resources for online vendors).
- Finding something that will distract you might just make that 30-minute workout bearable, and believe it or not you might even look forward to it! After all, it could be the only 30 minutes in your day that you have all to yourself. Indulge!
- Aerobic exercise videos and DVDs are also effective if you use them! They are convenient if you prefer to work out at home instead of taking a class at a studio or a gym, and there are hundreds to choose from. I suggest that you check out Collage Video (http://www.CollageVideo.com), or give them a call and ask for a recommendation.
- Also check if your local library rents exercise videos on tape or DVD. And by the way, there are videos for all types of activity; from weight training, to tai-chi, to stretching.
- Check out all the possibilities to add flexibility and strength training to your cardio workout.
List of 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:
- 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.
- 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.
- 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).
- 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!
There you have it. Aerobic exercise is awesome stuff! It strengthens your heart, adds strength to your muscles and makes them more efficient fuel-burners, increases your endurance and your energy, improves your mood, makes you fit and healthy, and much, much more. It could take as little as 30 minutes out of your day for a tremendous payoff so I suggest giving it a shot. Follow my advice for getting started by doing only what is realistic and build up slowly. You have only health and fitness to gain, and you're worth it! Good luck!
Can aerobic exercise prevent diabetes, heart disease, obesity, and weight control?
No study has been more conclusive about the role of healthy lifestyle changes (diet and exercise) in preventing diabetes than the Diabetes Prevention Program. It was a study of more than 3,000 individuals at high risk for diabetes who lost 12-15 pounds and walked 150 minutes per week (five 30-minute walks per day) for three years. They reduced their risk of diabetes by 58%. That's significant considering there are 1 million new cases of diabetes diagnosed each year. Aerobic exercise can also improve insulin resistance. Insulin resistance is a condition in which the body doesn't use insulin properly, and this condition can occur in individuals who do and do not have diabetes. Insulin is a hormone that helps the cells in the body convert glucose (sugar) to energy.
Many studies have shown the positive effects of exercise on insulin resistance. In one, 28 obese postmenopausal women with type 2 diabetes did aerobic exercise for 16 weeks, three times per week, for 45-60 minutes, and their insulin sensitivity improved by 20%.
The list of studies that show that aerobic exercise prevents or reduces the occurrence of cardiovascular disease is so long that it would take this entire article and probably five others just like it to review all of the research. One of the most important is one of the earliest. In a study of more than 13,000 men and women, it was shown that the least fit individuals had much higher rates of cardiovascular disease than fit individuals -- in some cases, the risk was twice as high. Aerobic exercise works in many ways to prevent heart disease; two of the most important are by reducing blood pressure and allowing blood vessels to be more compliant (more compliant means that they become less stiff and it's less likely for fat to accumulate and clog up the vessels). Results like these have been proven over and over again.
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 30 and 40 minutes of vigorous exercise several times per week, to 45 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. These are general guidelines, and so again, you need to experiment to see what works for you.
Scientists have recently become interested in the effects of aerobic exercise on cognitive function. It has been shown in rats that use of a running wheel every day stimulates new brain cells to grow in as few as 12 days. Brain cells in humans can't be studied directly, but what has been shown is that rates of dementia and Alzheimer's disease are lower in older individuals who exercise three or more times per week compared with older adults who exercise fewer than three times per week. In some cases, the risk is 62% lower. Evidence is also accumulating that active individuals perform better on cognitive function tests such as tests of memory and spatial relations than sedentary individuals.
Can aerobic exercise prevent cancer, osteoporosis, depression?
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.
Colon cancer. Research is clear that physically active men and women have about a 30%-40% reduction in the risk of developing colon cancer compared with inactive individuals. It appears that 30-60 minutes per day of moderate- to vigorous-intensity physical activity is needed to decrease the risk, and there is a dose-response relationship, which means that the risk declines the more active you are. Breast cancer. There is reasonably clear evidence that physically active women have a greater reduction in risk compared with inactive women. Like colon cancer, it appears that 75 to 150 minutes per day of moderate- to high-intensity physical activity is needed to decrease the risk, and it is likely that there is a dose-response relationship as well. Prostate cancer. Research is inconsistent regarding whether physical activity plays any role in the prevention of this cancer. Lung cancer. There are relatively few studies on physical activity and lung cancer prevention. The available data suggest that physically active individuals have a lower risk of lung cancer; however, it is difficult to completely account for the risks of active and passive cigarette smoking as well as radon exposure. Other cancers. There is little information on the role of physical activity in preventing other cancers.
There's some good news for people undergoing cancer treatment. In one study, aerobic exercise performed five days per week for 30-35 minutes for six weeks at 80% of maximal heart rate reduced fatigue in women being treated for cancer. In another study, 10 weeks of aerobic exercise at 60% of maximum heart rate for 30-40 minutes, four days per week, reduced depression and anxiety in female cancer patients. Aerobic exercise isn't a panacea when it comes to cancer, but evidence suggests that it certainly can help.
Osteoporosis is a disease characterized by low bone density, which can lead to an increased risk of fracture. The good news is that exercise may increase bone density or at least slow the rate of decrease in both men and women. It may not work for everyone, and the precise amount and type of exercise necessary to accrue benefits is unknown, but there is evidence that it can help. In children there is good news, too. It seems that active children have greater bone density than sedentary children and that this may help prevent fractures later in life.
Most of us who exercise regularly understand that exercise can elevate our mood. There have been a number of studies investigating the effects of exercise on depression. In one of the most recent studies, it was shown that three to five days per week for 12 weeks of biking or treadmill for approximately 30 minutes per workout reduced scores on a depression questionnaire by 47%. It's not a substitute for therapy in a depression that causes someone to be unable to function (in which case medication and/or psychotherapy may be necessary), but for milder forms of depression, the evidence is persuasive that it can help.
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Blair, S.N., et al. "Physical fitness and all-cause mortality. A prospective study of healthy men and women." JAMA 262.17 Nov. 3, 1989: 2395-2401.
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