Exercises that rely on the heart and lungs to supply oxygen to the working muscles for energy production are called cardiorespiratory or "aerobic" activities. Aerobic exercises involve large muscle groups, in a rhythmical fashion, at low-to-moderate intensities, for extended periods of time. For example, walking, jogging, swimming, cycling and aerobic dance are all considered aerobic exercises when conducted at appropriate intensities.

The most accurate method of determining level of aerobic conditioning is by measuring the maximal amount of oxygen the body can take in, transport, and use to form energy. The direct measurement of these capabilities can only be done in a laboratory and is called the VO₂max, or maximal oxygen consumption.

Regular aerobic exercise results in an improvement in aerobic fitness (VO₂max) along with associated health benefits. Consistent exercise reduces the risk of developing heart disease, diabetes, and osteoporosis. It is valuable in the long-term control of body weight and in maintaining physical capability during aging.  Additionally, many individuals experience an increase in mental functioning, greater daily energy levels, improved emotional state and ability to handle stress, and a more positive outlook about life. 

The cardiorespiratory system refers to the heart/circulatory system, which transports oxygen and nutrients in the blood to the working muscles, and the respiratory system, which loads oxygen into and removes carbon dioxide from the blood. 

Acute responses are those that occur during exercise, and include increases in heart rate, stroke volume (amount of blood pumped per beat) and blood pressure, all of which result in greater blood flow to the working muscles. Ventilation (breathing) also increases in order to meet the oxygen loading and carbon dioxide unloading requirements during exercise.

Chronic responses (longer-term adaptations) include an increase in VO₂max resulting from a greater stroke volume and specific muscle cell changes. Due to the increase in stroke volume with training, heart rate decreases at rest and during submaximal exercise. This indicates an improvement in aerobic conditioning.  

Most healthy people can begin a low or moderate exercise program without the need for a medical evaluation.  Those having risk factors for heart disease, joint problems, or who have been sedentary and are beyond age 40 (50 for women) should consult with their physician before beginning an exercise program, especially if it is vigorous. Certainly, anyone with symptoms and/or known cardiovascular disease or diabetes should have a medical check-up prior to beginning an exercise program.  

 As stated in lesson 2, an exercise prescription should include guidance concerning the mode or method (what to do), frequency (how often), duration (how long), intensity (how hard), and progression (stages) of the exercise program. The following guidelines relate to achieving “health-related” fitness.  

For cardiovascular (aerobic) fitness, the mode should include exercises that utilize large muscle groups, are rhythmic, safe, and can be easily continued for long periods of time at moderate intensity. Good aerobic activities include, but are not limited to: brisk walking, jogging, rollerblading, stationary and road cycling, aerobic dance, and swimming. The activity should be one the participant enjoys, has the equipment, knowledge and skill to perform, and can be conveniently practiced.

The frequency of aerobic activity depends somewhat on lifestyle and whether body weight control is a goal.  A frequency range of 3-7 days per week is the standard recommendation.  Although increases in aerobic fitness may result from exercising as little as 3 days per week, those wishing to lose body weight or who enjoy exercising more often, may exercise 5-7 days per week.  

If exercising often, adults should not engage in high-impact activities (those such as jogging, where the body becomes temporarily airborne) on successive days or else repetitive strain injuries might occur. Cross-training, or mixing of activities, is an effective way to train on successive days, fight boredom, and reduce the chances of developing overuse injuries.

Aerobic exercises should be continued for longer periods of time at low-moderate intensity. The duration should be 20-60 minutes of continuous activity for most adults. For example, most adults can complete a 3-mile brisk walk in 45-60 minutes.  Those with specific health problems or low exercise tolerance can benefit from breaking the 30-60 minutes up into several shorter exercise sessions. Additionally, a good rule for busy adults is to avoid exercise sessions which last beyond one hour. 

Proper intensity of aerobic activity is important for safety and effectiveness reasons. The standard recommended range is 50-85% of VO₂max, or 12-16 on the RPE (Rating of Perceived Exertion—discussed below). Those with very poor fitness levels and/or other health problems may, however, benefit from exercise intensities as low as 40% VO₂max, and 10 on the RPE. It is wise to keep intensity low during the initial stage of the aerobic exercise program and then proceed to gradually increase to moderate intensity during the improvement stage. Click the link below to see instructions on how to calculate an appropriate target heart rate training zone (THR) and an explanation of the rating of perceived exertion scale (RPE).   

(link to calculation of target heart rate training zone and RPE not yet available)   

The aerobic exercise program should progress from an initial, “break-in” stage of approximately 3-weeks, to an improvement stage lasting about 6-months, to lifetime maintenance of the fitness habit. As stated in lesson 2, the goal of progression is to gradually overload the aerobic system by increasing the frequency, duration and intensity of the activity until arriving at a reasonable, appropriate amount of exercise that can be maintained for life. It is important, when overloading for aerobic conditioning and weight control, to increase the duration of the exercise session before increasing the intensity.

   (link to week-by-week CV training program not yet available)