Aerobic Exercise Part 6

Last month, I explained the factors that should be considered when selecting a mode of exercise to train your cardiovascular system. An aerobic exercise overload is specific to cardiovascular function; therefore, exercise that involves rhythmic contractions of large muscle groups at a sustainable intensity level is the best way to train your heart. This type of training is also called endurance exercise because it improves your stamina. Conversely, strength training will not specifically overload cardiovascular function, so even though working with weights is extremely important for musculoskeletal health, it should only be done in addition to (as opposed to in place of) aerobic training.

Once you have chosen the appropriate mode(s) of endurance training to suit your specific circumstances, the other variables that define an aerobic training program can be determined. These include the frequency, duration and intensity of exercise. Much like mode, these parameters must be assigned based upon the requirements of the perspective exerciser and it is especially important to consider current physical fitness/health status, prior exercise history and long-term objectives when determining how hard, how long and how often a person will exercise aerobically. When in doubt, a conservative approach is always advisable for reducing the risk of injury or untoward event; however, there has been some debate in recent years regarding exactly how conservative the approach should be. After all, lying on your couch all day is the ultimate conservative strategy and clearly the best way to ensure no acute risks. However, from a chronic standpoint, the repercussions of that game plan are severe!

For many years, exercise physiologists have been trying to precisely define the optimal dose-response relationship for aerobic exercise (i.e., the volume of training that will yield maximal benefit with minimal risk). Unfortunately, this magic bullet is still elusive. One thing that is apparent, however, is that the optimal dose depends on the fitness level of the exerciser. For example, in less-fit subjects, frequencies of as little as two sessions per week can result in improvements in functional capacity (as indicated by the maximum amount of oxygen the person can consume; i.e., the “VO2 max”), but when a greater initial fitness level is present (for example, for individuals with a VO2 max of greater than 50 ml/kg/min), at least three are required. This works well because starting with fewer weekly sessions for beginners reduces the risk of them being overwhelmed and dropping out before exercise becomes part of their regimen and also ensures that frequency can be increased as the program proceeds to satisfy the tenet of progression.

While 2-3 aerobic sessions per week is believed to provide the minimal frequency stimulus necessary to induce positive cardiorespiratory adaptations, it has also been suggested that five represents the maximum. For example, the 1998 American College of Sports Medicine position stand suggests that minimal if any additional benefit can be achieved if more than five weekly sessions are performed; however, they do believe that the incidence of injury increases disproportionately when aerobic exercise is done that often. Consequently, they recommend 3-5 days per week to improve cardiorespiratory fitness. However, this position stand also is established based on the notion that the total energy expenditure accumulated throughout a week’s worth of physical activity is the key determinant of how much fitness level will be improved. This premise has been disputed by subsequent research.

Total energy expenditure as the critical determinant of the cardiovascular training stimulus implies that once a minimum intensity threshold that is relatively low is exceeded, the aerobic training effect will be similar for lower- compared to higher-intensity activities so long as they are performed long enough to engender a similar caloric outlay.  For example, five 30-minute sessions of four calorie-per-minute walking (e.g., a three mile-per-hour pace maintained by a 160-pound person) would be equally as beneficial as two 25-minute sessions of jogging at double that speed because the latter would cost 13 calories per minute for the same person, so each would involve total energy expenditure of 600-650 calories over the course of the week. This belief, therefore, provides the impetus for recommendations like “take the stairs instead of the elevator,” “park farther away and walk the extra distance” and “get out there and work in that garden every chance you get!” There are also those who suggest that accumulating more energy expenditure in less time (i.e., exercising at a higher intensity to accumulate the required amount) can be detrimental because it increases the risk of injury and burnout. Unfortunately, it now appears that this belief (and recommendations that are based upon it) might have little research-based support.

Overall energy expenditure is definitely the key determinant of whether you gain, lose or maintain body fat; however, even in this case, spending an additional 50 calories walking from the far end of the parking lot is somewhat negligible when you consider that 70 times that amount of energy is contained in one pound of stored fat. But to improve fitness, the total-energy approach is even more problematic. Recent research from Dr. Gary O’Donovan and colleagues in the U.K. indicates that the total volume of training must be considered relative to the time it takes to accumulate it. In other words, intensity matters!

This article was originally published in New Living Magazine, which can be accessed on-line at