Different clients have different goals, time frames and expectations, and they seek out fitness professionals for a variety of reasons. In addressing client needs, personal fitness trainers (PFTs) are also designing programs meant to improve the health-related components of fitness and reducing risk factors for chronic diseases. But how much exercise is enough to achieve the desired outcomes?
The parameters of the exercise prescription include frequency, intensity, time and type (or the FITT principle), which collectively determine the energy expenditure (calories) of the program. It has been suggested that the health benefits associated with a physical activity program are directly related to the total exercise volume or the calories expended (ACSM 2006). According to the dose-response relationships between physical activity and health benefits, the American College of Sports Medicine (ACSM) has recommended an energy expenditure in the range of 1,000–3,000 calories per week (ACSM 2006).
Yet, one shortcoming of this broad recommendation is a failure to account for individual differences in body weight, which may lead to significant over- or underestimation of energy expenditure. Recent studies have shown that energy expenditure recommendations based on individual differences in body mass resulted in significant improvements to cardiovascular fitness and risk factors for chronic diseases, including cholesterol, body composition and insulin sensitivity (Houmard et al. 2004; Kraus et al. 2002; Slentz et al. 2004).
The purpose of this article is to assist fitness and health professionals in designing improved exercise programs that identify the optimal energy expenditure requirements of their clients.
The dose-response concept refers to the interaction between the amount of exercise performed in an exercise program and the magnitude of health benefits garnered from that training regimen (ACSM 2006). Higher levels of exercise (dose) are associated with improved health benefits (response); conversely, lower levels of exercise (dose) are linked to diminished health benefits (response).
Exercise dose can be measured as the frequency, intensity and/or duration of an exercise program. More commonly, dose is quantified as the combination of these variables and expressed as energy expenditure. Like the nutritional value of food, energy expenditure is reported in the units of calories (kcal). The energy expenditure of an exercise program can be quantified by using metabolic calculations for various exercise modes, which are derived from the workload–energy expenditure relationship. (“Calculating Caloric Expenditure” by Jeffrey Janot, PhD, in the June 2005 issue of IDEA Fitness Journal focused on determining the energy expenditure of an exercise program using metabolic calculations.)
Manipulating the exercise dose is done with the intent of eliciting a positive physiological response, which may be increased cardiovascular fitness, improved cholesterol profile or lowered blood pressure.
Note: When designing exercise programs, fitness professionals should consider not only the optimal dose of exercise that will result in the greatest benefit, but also the potential risks associated with an increased amount of exercise. In particular, the risk of musculoskeletal injury will be greater with an increasing volume and intensity of exercise.
Scientific research has demonstrated that there is a dose-response relationship between exercise and multiple health outcomes (see Table 1), including cardiovascular fitness level, risk of coronary artery disease (CAD) and all-cause mortality, obesity, cholesterol profile, type 2 diabetes and colon cancer (MacKinnon et al. 2003). Based on these dose-response relationships, both ACSM and the U.S. Surgeon General have noted that the health benefits of a program are associated with the total weekly energy expenditure (ACSM 2006; U.S. Dept. of Health and Human Services 1996). ACSM has recommended a target energy expenditure of 150–400 kcal per day. The lower end of this range corresponds to 1,000 kcal per week, while the upper end is equivalent to approximately 3,000 kcal per week (ACSM 2006). Currently, PFTs are encouraged to design initial exercise programs to achieve the lower threshold (1,000 kcal per week), and then to progress gradually toward the higher end of the recommended range (3,000 kcal per week).
While there is compelling evidence based on the dose-response relationship between exercise volume and health benefits to support the absolute energy expenditure recommendations (1,000– 3,000 kcal per week) of ACSM and the U.S. Surgeon General, it is important to note that the number of calories burned during the same exercise session will be dissimilar among individuals of differing body weights.
Table 2 illustrates Jack and Jill: two individuals of different ages, body weights and genders following precisely the same exercise routine for 1 week. While this exercise program yields a weekly energy expenditure of 750 kcal for Jill, the same program leads to an energy expenditure of 1,250 kcal per week for Jack. The primary reason for the difference in weekly energy expenditure is the variation in body weight.
Is it correct to say that everyone, young or old, male or female, big or small, should follow the same absolute energy expenditure recommendation to achieve equivalent health benefits? In our example, should an exercise professional encourage Jill to extend her daily exercise duration so as to increase her weekly energy expenditure to 1,000 kcal per week? Conversely, should Jack be advised that his weekly energy expenditure is actually higher than the 1,000-kcal-per-week recommendation—and that he should therefore consider decreasing his daily exercise duration? This scenario places fitness professionals in an uncomfortable position. They are faced with answering the question, Is an absolute weekly energy expenditure recommendation appropriate for everyone?
We believe this approach introduces the possibility of under- or overestimating the energy expenditure requirements of individual exercise programs, thus diminishing the health outcomes for clients. Fortunately, recent research findings have identified an improved approach to designing exercise programs and individualizing weekly energy expenditure goals.
Recently, the Studies of a Targeted Risk Reduction Intervention through Defined Exercise (STRRIDE) have yielded several published papers focused on researching the dose-response relationship between weekly energy expenditure and various health outcomes, including cardiovascular fitness, cholesterol parameters, body composition measurements and insulin sensitivity (Houmard et al. 2004; Kraus et al. 2002; Slentz et al. 2004). The unique aspect of STRRIDE was the investigation of separate doses of weekly energy expenditure relative to body weight and their effect on health outcomes, rather than the examination of different absolute weekly energy expenditure levels.
In addition to a group of sedentary controls, one group performed a low-amount exercise program (14 calories per kilogram of body weight per week [kcal/kg/wk]), while a third group performed a high-amount exercise program (23 kcal/kg/wk). Each group was composed of approximately 40 male and female participants, aged 40–65 years. The exercise groups performed a combination of treadmill, bicycle and elliptical cross-trainer exercise for 6 months at an exercise intensity equivalent to 65%–80% of maximal oxygen uptake (VO2max). (Note: STRRIDE also examined the dose-response relationship between exercise intensity and various health outcomes, but further discussion of this aspect of the study—which involved a fourth group—is beyond the scope of this article.)
In a dose-response manner (comparing the control group, the low-amount group and the high-amount group), there were greater improvements in each of the health outcomes during the course of the study with increasing volumes of exercise. Cardiovascular fitness was higher in both the low-amount (16.7%) and the high-amount (17.8%) exercise groups following the 6-month program. While high-density lipoprotein (HDL) cholesterol worsened in the sedentary group (-1.4%), this outcome improved in both the low-amount (+0.6%) and the high-amount (+9.7%) groups (Kraus et al. 2002). Percent body fat increased in the sedentary group (+0.1%) but decreased in both the low-amount (-2.6%) and the high-amount (-4.7%) groups (Slentz et al. 2004). Finally, insulin sensitivity diminished in the sedentary group (-4%) but improved in both the low-amount (+38%) and the high-amount (+83%) groups (Houmard et al. 2004).
The findings from the STRRIDE study are important to fitness professionals for three major reasons:
1. They support the dose-response relationship between increased amounts of energy expenditure and greater health benefits.
2. The doses of energy expenditure prescribed are relative to individual differences in body weight.
3. The specific doses used in the study provide guidelines for developing individual exercise prescriptions for future clients.
How can you apply this information to customize exercise programs for clients with differences in body weight, gender and age? How can you design an individually appropriate exercise program that does not under- or overestimate a client’s energy expenditure requirements?
Let’s bring back Jack and Jill. Rather than design an exercise program that follows an absolute energy expenditure recommendation, our approach will shift to one that uses the STRRIDE study energy expenditure recommendations of 14 and 23 kcal/kg/wk, which are relative to individual differences in body weight. If we look at Table 3, it is apparent that based on differences in body weight, the relative weekly energy expenditure goals of the exercise programs for Jack and Jill are noticeably different.
The relative weekly energy expenditure goal for Jack is about 1,275 kcal per week, while Jill needs to achieve 770 kcal per week. Although this approach yields different absolute weekly energy expenditure goals, the discrepancy between the two programs is accounted for by the differences in body weight. Note that the parameters of the exercise programs are similar for Jack and Jill, which is in agreement with the ACSM FITT principle recommendations. In contrast, when we designed the programs for Jack and Jill according to ACSM’s and the U.S. Surgeon General’s absolute energy expenditure recommendations of 1,000 kcal per week, we were faced with the prospect of increasing or decreasing each client’s weekly exercise duration to achieve the target goal.
The dose-response relationship between exercise volume and health outcomes suggests that the major focus of exercise program design should be the total weekly energy expenditure. Traditionally, this approach has followed an absolute recommendation insensitive to individual differences, particularly in body weight. Clearly, an absolute energy expenditure recommendation increases the likelihood of over- or underestimating individual client needs. Overestimating the energy expenditure for a client may lead to an unrealistic goal, increasing the chance of injury or burnout and lessening exercise adherence. Conversely, underestimating the energy expenditure for a client can result in less than optimal health benefits, which can also decrease program adherence.
Recent findings from the STRRIDE study demonstrate that significant health benefits are conferred by designing exercise programs following energy expenditure recommendations relative to body weight. Fitness professionals can use the specific exercise doses of 14–23 kcal/kg/wk used in the study to formulate exercise programs for future clients. These relative energy expenditure recommendations would correspond to approximately 90–150 minutes of weekly exercise for Jack and Jill.
While the main difference in energy expenditure recommendations is related to body weight, PFTs also need to consider clients’ gender and age when designing exercise programs. Ultimately, individualizing weekly energy expenditure goals based on body weight, age and gender will result in optimal exercise programs that will better maximize health benefits.