The American College of Sports Medicine (ACSM) provides guidelines for stratifying clients before exercise testing and prescription (10). Stratification enhances safety of exercise participation and aids in exercise programming. Correct stratification requires knowledge of the client's risk factors, some of which may be unavailable to the practitioner. For example, fasting glucose and lipid values are unknown in the absence of a blood profile analysis. In addition to unavailable information, there are other risk factors that are difficult to quantify, further increasing the challenge associated with stratification. Current guidelines (10) have been updated to aid practitioners who may encounter clients having an incomplete risk profile. Still, practitioners must be well informed about current guidelines and prepared to integrate professional judgment when evaluating a client's risk level, choosing an exercise test, and prescribing appropriate physical activity.
ACSM's guidelines (10) state that the risk for cardiac arrest in physically active men is 40% that of sedentary men. Whereas exercise increases the acute risk of complications, this risk is considerably lower than that associated with a sedentary lifestyle. Considering the protective influence of exercise against disease, it would be a mistake to permit a potentially incorrect stratification to deter exercise participation. Franke (4) outlined five major components of an effective comprehensive exercise program using an acronym (MR IPL): Medical history, Risk factor assessment, Interpreting the data, Prescribing exercise, and Lifestyle counseling. Medical history and risk factor assessment function as gatekeepers to program entry and help ensure participant safety. Consequently, the importance of these components cannot be overstated. Adherence to professional stratification guidelines is highly encouraged in the initial two stages of Franke's model (4). Thus, client information remains critical. This article presents a three-step approach for stratification using ACSM guidelines, including instructions for working with clients whose risk factor profiles are incomplete. Furthermore, because the practitioner should use discretion when determining appropriate testing procedures and prescriptions, advice is offered on the integration of professional opinion into these decisions.
CURRENT ACSM GUIDELINES
In keeping with the current knowledge base, ACSM periodically revises its Guidelines for Exercise Testing and Prescription, which is currently in its eighth edition (4). Pescatello et al. (9) recently provided a brief history of ACSM guidelines and a general overview of the eighth edition contents. The current article will focus on stratification, a single component of these guidelines.
Primary components of ACSM stratification guidelines are (a) stratification categories, (b) risk factors and signs/symptoms used for stratification, and (c) recommendations regarding the need for a physician's presence during exercise testing or physician's clearance before prescribing exercise. Stratification involves determining the presence of previously diagnosed disease, evaluation of the total number of risk factors, and consideration of signs/symptoms suggestive of possible disease. The current ACSM guidelines (10) stratify all individuals as either low, moderate, or high risk based on client profile. Table 1 summarizes stratification criteria.
Client stratification into the low or moderate risk categories requires absence of diagnosed disease and no signs/symptoms suggestive of underlying cardiovascular, pulmonary, or metabolic disease (e.g., ankle edema, dizziness/syncope, known heart murmur) (10 p. 26-27). In addition, the low risk classification requires that no more than one risk factor is present, whereas the moderate risk designation is appropriate when presenting with two or more risk factors. A client is only stratified at the high risk level as a result of diagnosed disease or the presence of one or more signs/symptoms (regardless of total number of risk factors). It is important to note that low or moderate risk hinges on satisfying all three criteria (no diagnosed disease, no signs/symptoms, and no more than one risk factor). High risk, however, is determined solely because of diagnosed disease or presence of signs/symptoms, independent of risk factors. For example, an elite endurance athlete with a heart murmur (a sign/symptom) would be classified as high risk. However, a 90-year-old individual and an 18-year-old individual both having no signs/symptoms and no known disease would be stratified at the low or moderate risk level based on their risk factors. Regarding age, previous guidelines automatically stratified men older than 45 years and women older than 55 years at the moderate risk level (provided they had no signs/symptoms and no diagnosed disease) (12). The latest guidelines (10) use the age criteria as one of eight risk factors rather than permitting this factor to independently dictate low versus moderate risk stratification. The consequence of this change is that individuals meeting or exceeding the previous age criteria may now be stratified as low risk, provided age is their only risk factor. In all cases, the presence of risk factors is important for evaluating overall risk, but only influences low versus moderate risk stratification.
The current ACSM guidelines (10) provide a detailed flow chart of the sequential steps in stratification (Figure). The following is a simple three-step approach the practitioner can use in conjunction with the flow chart.
- Assess the presence of previously diagnosed disease
Assess the presence of signs/symptoms (Table 2.2 of Thompson (10))
- If cardiovascular, pulmonary, or metabolic diseases are present → stratify the client as high risk (risk factors and signs/symptoms should be assessed but are not needed for stratification)
If there is no diagnosed disease and no signs/symptoms, then determine the total number of risk factors present (Table 2)
- If one or more signs/symptoms are present → stratify the client as high risk (risk factors should be assessed, but are not needed for stratification)
- Presence of two or more risk factors → stratify as moderate risk
- Presence of zero or one risk factor → stratify as low risk
Clients having no diagnosed disease and no signs or symptoms for cardiovascular, pulmonary, or metabolic disease will not be stratified at the high risk level. In these clients, the total number of risk factors will determine the low or moderate risk stratification. Determining the presence/absence of certain risk factors can be difficult because some factors are not easily assessed, particularly outside a clinical setting. Hypertension is defined as a systolic blood pressure (BP) greater than or equal to 140 mmHg or a diastolic BP greater than or equal to 90 mmHg confirmed by measurements on at least two separate occasions or being on hypertensive medication (10). Although BP is easily measured and results are immediately available, obtaining sequential measurements may require unnecessary suspension of the exercise test or prescription. Dyslipidemia has a lengthy definition: low-density lipoprotein greater than or equal to 130 mg/dL (3.37 mmol/L) or high-density lipoprotein less than 40 mg/dL (1.04 mmol/L) or on lipid-lowering medication. If only total cholesterol level is available, a value of greater than or equal to 200 mg/dL (5.18 mmol/L) is the criterion for confirming dyslipidemia (10). Similar to lipid status, determining whether "prediabetes" is present as a risk factor requires a blood profile. Obviously, this information is needed for stratification but may be unknown or unavailable for many clients. For example, assume that the lipid values and blood glucose levels are unknown, and the client has one definitive risk factor. If either or both unknown risk factors (dyslipidemia or prediabetes) are present, the client would be stratified as moderate risk rather than low risk, thus altering decisions regarding testing and prescription. Another consideration is the volatility of the measures that define some risk factors. For example, acute factors such as anxiety can influence BP, whereas fasting glucose and lipid profiles also are subject to day-to-day variation. If measurements are just above or below the specified criteria (i.e., fasting glucose, ≥100mg/dL), stratification could change day-to-day. Previous ACSM guidelines (5,6,8,12) did not address how to stratify clients who have incomplete profiles. However, current guidelines (10) state that when the presence of a risk factor is undisclosed or unavailable, the practitioner should count it as a risk factor (except for "prediabetes," which is further dependent on age and body mass index). Such procedures have provided clarity to stratification procedures and helped the practitioner adhere to the conservative approach forwarded by ACSM.
A sedentary lifestyle is included as one of the eight risk factors. Therefore, another challenge for the practitioner is determining the client's physical activity status. The definition of sedentary lifestyle was adopted from the Surgeon General's report (11) ("…not participating in at least 30 minutes of moderate-intensity [40%-60% V˙O2 reserve] physical activity on at least 3 days per week for at least 3 months"). It is not difficult to determine the presence of this risk factor for highly active individuals or clients who clearly report low physical activity. However, when clients report some activity but there is a question as to whether the threshold as defined by the guidelines is achieved, the practitioner must use judgment. To aid in making this determination, the client can be questioned regarding activity habits. A simple instrument, the International Physical Activity Questionnaire (http://www.ipaq.ki.se), is available to help with this assessment. Determining prior activity requires input from the client, and the practitioner should be aware that overestimating physical activity is common (2,7). As with the other factors, inclusion/exclusion of sedentary lifestyle may potentially alter a client's stratification.
Obesity is defined as body mass index (BMI) greater than or equal to 30 kg/m2 or waist girth greater than 102 cm (40 inches) for men and greater than 88 cm (35 inches) for women. Although the relative risk of various chronic diseases can be effectively predicted using BMI (1), one criticism of BMI is its lack of consideration of body composition. Therefore, ACSM (10) suggests "…exercise professionals should use clinical judgment when evaluating this risk factor." Rather than BMI, alternative assessments such as body fat percentage estimation using skinfold measures may be more appropriate in assessing obesity status, particularly in special populations such as athletes.
In summary, well-defined risk factors (e.g., dyslipidemia, glucose measures associated with prediabetes) require blood analysis and consequently are not as commonly known by clients. Other factors are noninvasively measured, yet are potentially more difficult to assess because of subjectivity (e.g., sedentary lifestyle, obesity). As such, the challenges faced by the practitioner include (a) stratifying clients who do not have a complete risk factor profile perhaps because of missing blood variables and (b) stratifying clients in cases where specific risk factors are somewhat difficult to assess with precision (e.g., obesity, sedentary lifestyle). Even with the positive advances in the current ACSM guidelines, the practitioner's professional opinion and judgment remain important.
INTEGRATING PROFESSIONAL OPINION
Stratification represents an effort to determine the level of risk in anticipation of a pending exercise test or an increase in physical activity level. Stratification may often hinge on the proper assessment of a combination of risk factors and clinical measures heavily influenced by lifestyle. Guidelines use a categorical system (low, moderate, or high risk) to reflect a continuous variable. Because of the continuous nature of risk, two individuals who are both correctly stratified at the moderate risk level may not represent the same level of risk. For example, a 46-year-old marathon runner with a family history of disease and an individual exceeding the threshold for all eight risk factors are both classified as being at moderate risk, yet intuitively they would have dissimilar risks for completing an exercise test or increasing exercise participation. ACSM (10) implies that professional judgment is often necessary and that guidelines provide only a general direction and should not necessarily be applied in a rigid manner. Therefore, integrating professional opinion becomes increasingly important in stratification and decision making. In particular, professional opinion is important when the limitations previously discussed hinder stratification. ACSM deems physician involvement not necessary for low-risk clients performing a submaximal or maximal test or beginning a prescription of moderate or vigorous exercise (10). For moderate-risk clients, however, guidelines recommend a physician's presence during maximal testing and medical examination before prescribing exercise at a vigorous intensity. For submaximal testing and moderate exercise prescription for clients at the moderate risk level, physician involvement is regarded as not necessary, but is not discouraged.
The authors of the current ACSM guidelines are to be commended for directly addressing how to handle undisclosed or unavailable risk factors, making guidelines-based stratification highly conservative yet always possible. However, as stated, risk level exists on a continuum rather than a categorical scale. Consequently, practitioners are encouraged to not only adhere to the guidelines, but to remember that within a given risk category, individuals will likely differ with respect to risk level. A client having five of eight risk factors including an age of 75 years and sedentary lifestyle is an entirely different case from a 21-year-old marathon runner who simply does not know his or her BP or has not had a lipid profile assessment (although both individuals would be stratified at the moderate risk level). As noted, when stratification is made at the moderate level, the guidelines recommend a physician's clearance before prescribing vigorous exercise and before completing a maximal test. For stratification at the low-risk level, guidelines indicate that physician involvement is not necessary. The factors arguably driving decisions regarding testing and prescription should be based on professional judgment.
Maximal Versus Submaximal Testing
When deciding between submaximal and maximal testing, risks versus benefits should be considered. To justify the increased risk associated with maximal testing, comparable benefits must accrue from the maximal test. Maximal testing offers improved sensitivity in diagnosing the presence of disease in asymptomatic patients (10). However, such diagnoses are completed by physicians rather than the exercise professional. In addition, such testing is more uncomfortable and more likely to result in complications caused by elevated cardiovascular demand (10). Therefore, the question must be asked, "What is gained by conducting a maximal (vs. submaximal) test?" Compared with submaximal protocols, maximal protocols do offer certain advantages. If a metabolic measurement system is available, direct measures of maximal oxygen consumption (V˙O2max) may be made and would certainly be superior to estimating V˙O2max. In addition, measured maximal heart rate is more accurate than using equation-based estimates. Ventilatory threshold is another useful prescription tool that can be assessed from maximal testing. Consequently, exercise prescription accuracy is enhanced when using results from a maximal versus submaximal test. However, an extremely detailed fitness assessment is not required for an individual to benefit from a physical activity program and, consequently, the risks associated with maximal testing often outweigh potential gains. Client-centered goals are of major importance. From a public health perspective, most clients would most likely benefit from programs designed to enhance health-related fitness and modify disease risk. In these clients, the value of maximal testing is questionable. Although less accurate, submaximal protocols permit estimations of fitness that can be tracked over time and provide guidance for progression of appropriate prescriptions. Significant health benefits occur with regular participation in moderate-intensity physical activity (10,11). Such a prescription does not require a maximal test. Conversely, clients interested in vigorous exercise and possibly competition may well benefit from the precision gained from maximal testing. For those stratified as low risk and seeking only to lower disease risk through exercise participation, it may be difficult to justify a maximal (vs. submaximal) test based only on the enhanced accuracy of the exercise prescription. The practitioner should make decisions using not only stratification, but also client goals.
Test data from fitness evaluations may provide a method for evaluating a client's progress. Participation in an exercise program may positively alter certain risk factors such as cholesterol level or BP. The transient nature of risk factors makes periodic reevaluation a requisite for determining stratification level and the associated risks. Practitioners should pay careful attention to all risk factors rather than focusing too heavily on fitness assessment. Disproportionate emphasis on fitness could result in other vital factors being overlooked. Alternatively, viewing factors globally, as with stratification, may offer a more prudent estimation of risk. A maximal test provides an accurate assessment of the condition of the cardiovascular system and also can permit detection of symptoms at certain metabolic loads, assisting in implementing a symptom-limited exercise prescription. Although this is important and stress testing can be functionally valuable, particularly in clinical settings, the decision to conduct a maximal test should be dependent on client goals, with serious consideration given to the benefits (if any) that might be gained. Conservatively, maximal testing can be difficult to justify for individuals interested principally in health-related components.
Moderate Versus Vigorous Prescription
Outlining an appropriate exercise program in the current context requires a clarification of "moderate" and "vigorous" exercise. Intensity is the single variable delineating between moderate and vigorous exercise. This is a prudent approach because intensity determines acute cardiovascular demand and subsequent risks during exercise. Moderate exercise is defined by ACSM (10) as 40% to 60% V˙O2max, 3 to 6 METS, or an intensity well within the individual's current capacity that can be comfortably sustained for a prolonged period. Vigorous exercise is defined as greater than 60% V˙O2 max, greater than 6METS, and is "intense enough to present a substantial cardiorespiratory challenge" (10). Note, however, that 4 METS may be moderate for a fit person yet vigorous for another if it exceeds the 60%V˙O2max threshold. Simply stated, the practitioner should remember that intensity depends on the individual, and therefore a client's fitness level should be carefully considered to ensure that an exercise program is initiated at an appropriate intensity. A prudent practice is to use the absolute and relative criteria for moderate and vigorous exercise in a conservative manner when developing the program.
Exercise prescriptions are made as clients prepare to initiate a physical activity regimen. Without a physician's clearance, low-risk clients may begin a moderate or vigorous program, whereas guidelines suggest that moderate-risk clients begin at a moderate intensity. A critical point is that program initiation often presumes a previously low level of activity. For such clients, it is difficult to justify beginning a vigorous (vs. moderate)-intensity exercise program. Rather, a more judicious approach is to prescribe moderate-intensity physical activity, which presents several advantages. First, this assists in assuring safe participation and allows progression to a more vigorous program based on client feedback regarding tolerance. Conversely, initiating a program at a vigorous level increases the risk of acute complications (possibly in a client who was difficult to stratify).
If a cardiovascular event should occur, irreparable damage or death could result. Clearly, it is better to avoid such issues, if at all possible. From this perspective, prescriptions should be primarily initiated at a moderate (rather than vigorous) level. Exceptions might include individuals who are currently active but unaware of their fasting glucose or lipid profile (resulting in stratification at a "moderate" level). Even for this population, advancing an initially moderate-intensity prescription that can be increased in intensity offers a more conservative but safer approach.
Another rationale for initiating moderate versus vigorous exercise is compliance. Prescribing a regimen that is well-tolerated by the client is an appropriate way to enhance adherence. With clients who are just beginning an exercise program, the increased physical activity should be perceived as pain free and enjoyable (3). With significant health benefits possible from moderate-intensity exercise, it is advantageous to design a well-tolerated moderate-intensity prescription that maximizes compliance rather than to advocate a vigorous program that may overwhelm a client and cause one to drop out.
Professional guidelines provide excellent direction for client stratification. The most recent ACSM guidelines have been enhanced to include instructions for practitioners faced with undisclosed or unavailable risk factor information. A simplified approach to stratification involves evaluating, in order, (a) known disease, (b) signs/symptoms, and (c) risk factors. Even with complete and detailed client risk factor information, professional judgment is often necessary. Evaluation of the guidelines and attention to client-centered goals leads to a conservative approach regarding stratification, exercise testing, and exercise prescription. Although physical activity acutely increases risk, potentially more severe consequences accompany a sedentary lifestyle. Safer and more easily tolerated submaximal testing provides less precise information regarding fitness, resulting in a less precise prescription. However, for promoting health-related fitness, such testing is appropriate. Similarly, an exercise prescription of moderate intensity assists in achieving health benefits and, when compared with a vigorous prescription, results in a relatively lower risk of complications and may ensure optimal compliance. Practitioners are encouraged to use professional guidelines when stratifying clients, but also to integrate professional judgment regarding testing and prescription with client safety and goals as paramount factors in making decisions.
CONDENSED VERSION AND BOTTOM LINE
ACSM stratification is simplified by a sequential evaluation of (a) known disease, (b) signs/symptoms, and (c) risk factors. When presented with incomplete client profiles, the practitioner should follow current conservative guidelines for stratification and apply prudent judgment with special consideration of the client's fitness level and intended goals when prescribing exercise. Because beginners and those interested in health benefits arguably should not initiate a program at a vigorous level, a conservative approach involving submaximal testing and a moderate-intensity prescription is encouraged for this population.
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