Lack of patient adherence to intervention has been labeled a“risk factor” for cardiovascular disease(12). It has been reported that only 21.8% of heart disease patients recall the recommendation to participate in a cardiac rehabilitation program and that only 35.4% of these patients actually enroll in a program (10). For an exercise program to be successful, patients must receive a therapeutic dose of exercise. The benefits of exercise are realized only during the period of time that a patient participates in an exercise program and are lost with the cessation of exercise (2). The difficulties of maintaining cardiac rehabilitation patients on therapeutic exercise programs are well documented(2,13). Intensity levels and perceived effort are negatively associated with adherence (6). The success of an exercise program in a cardiac rehabilitation program is related to the patient's physical ability to perform the prescribed exercise, time commitment on a regular basis, and his perceived benefit of the program(5,8).
In the Training Levels Comparison (TLC) trial, two training programs, high and low intensity, with target heart rates which corresponded to 50% and 85% of the ˙VO2max established on the previous exercise test, respectively, were compared to determine whether the high intensity training program conferred additional cardiac benefit over the low intensity training program of the same duration in sedentary men between 30 and 67 yr of age with documented evidence of coronary heart disease (11). Although the primary outcome variable for the study was the 1-yr change in peak exercise left ventricular ejection fraction, the duration of participation in the exercise intervention was 2 yr to determine whether continued exercise was associated with further improvement in cardiac function.
Cardiac benefit from exercise training is highly dependent on attendance at exercise sessions and achievement of the target heart rate. Potential benefits associated with exercise training may be compromised by low attendance at exercise sessions. If the separation between the two treatment groups with respect to achieved heart rates is inadequate, it is unlikely that a difference in the outcome measure of left ventricular function would be observed.
This paper reports on two components of adherence: 1) attendance at exercise sessions monitored as a measure of participant adherence, and 2) achievement of the protocol defined target heart rates monitored to determine whether the intervention of assigning target heart rates resulted in different levels of achieved heart rates.
The study was conducted at two clinical centers, the University of Alabama at Birmingham (UAB) and Emory University. To be eligible, patients had to be male and between 30 and 67 yr of age and had to have at least one of the following within the 2 yr preceding enrollment: angiographic evidence of at least 70% stenosis in one major coronary vessel as defined in the CASS study(16); myocardial infarction, coronary artery bypass graft; or percutaneous transluminal coronary angioplasty. Patients had to be able to perform three METs of exercise, and reside within 50 miles of a clinical center. All patients signed an informed consent form in which they agreed to the use of medical information collected as part of the study. Exclusion criteria were uncontrolled congestive heart failure, unstable dysrhythmia, unstable angina, uncontrolled diabetes mellitus, uncontrolled systemic hypertension, exercise-limiting concurrent condition, any major cardiovascular condition or procedure that is not an inclusion criteria, reported alcohol intake of 21 drinks or more per week, and participation in a regular exercise program at an intensity level greater than walking at a usual pace.
To identify individuals likely to maintain interest in the study for 2 yr, potential participants were required to attend at least four of five 1-h education sessions during a 2-wk screening period to enroll in the study. These sessions served to educate patients about their disease and risk factors, as well as to impart information regarding the objectives of the study and the benefits of participation. The General Health Rating Index(3), a 22-item measure of perceptions of health status, was administered at the initial evaluation to determine its association with adherence.
To enhance attendance during the study, spousal support and participation in the exercise program were encouraged. Group meetings were held for patients and their spouses to maintain interest in the study and to develop rapport with the clinic personnel. Frequent counselling sessions with individual patients and their spouses were held. Individual patient attendance rates were posted on a monthly basis. During exercise sessions, patients monitored their heart rates to achieve or maintain their heart rate in the target range. Since patients in both intensity groups exercised together, adherence promotion strategies were implemented consistently across treatment groups. Uniformity between clinical centers was facilitated by regular conference calls and meetings with staff members from both centers.
Patients who enrolled in the study were randomized to participate in either the low intensity or high intensity exercise program for 2 yr. All patients were to participate in 1-h long exercise sessions directed by an exercise physiologist three times per week on nonconsecutive days. Attendance logs were maintained for each patient. At 3 months, 6 months, 1 yr, and 2 yr post-randomization, patients underwent upright exercise testing on a treadmill according to the modified Bruce protocol (1).
A total of 200 patients enrolled in the TLC trial. Three patients were missing demographic information and were excluded at baseline from the analysis. A simple randomization scheme was implemented that led to unequal numbers of patients in the two treatment groups. There was no investigator bias in the treatment assignments.
At the initial evaluation, patients were administered a questionnaire regarding demographic characteristics, physical activity, and health habits. To assess alcohol use, patients were asked to estimate their weekly consumption of beer, wine, and hard liquor with one can of beer, one glass of wine, or one shot of liquor counted as the equivalent of one drink. Smoking status was determined by patient self-report as a current cigarette smoker, ex-cigarette smoker, user of other tobacco products, or as never having smoked cigarettes. Patients were asked to rate their physical activity within the 6 wk prior to the initial evaluation in one of three categories: level 1, little or no physical activity; level 2, occasional physical activity; or level 3, regular physical activity at least 3 times per week. Physical activity included work and leisure activities that required sustained physical exertion such as walking briskly, jogging, lifting, and carrying items.
For each patient, the attendance rate was defined as the percent of total exercise sessions attended and was determined for years 1 and 2. No adjustment was made for sessions missed involuntarily due to illness or other reasons. The mean heart rate from the six exercise sessions preceding the evaluations at 6 months and 1 yr were taken as the achieved heart rates. Information on the target and achieved heart rates were available at 6 months for 156 patients and for 130 at 1 yr. To evaluate the degree to which adherence to the target heart rate was attained, the achieved heart rate and the proportion of patients whose achieved heart rate was within 5 beats·min-1 of the target were evaluated.
A two-way analysis of variance was performed to evaluate the effects of treatment assignment (low intensity, high intensity) and time (year 1, year 2) on the attendance rate. For each treatment group, the effects of the following demographic and clinical characteristics on attendance were evaluated using an analysis of covariance: time, clinical center (UAB, Emory), race (white, black), age, marital status (married, other), highest educational level achieved (post-high school, other), work status (full-time, other), exercise activity at enrollment (little/none, occasional/regular), alcohol use (≥7 drinks per week, other), smoking status (current smoker, ex-smoker or nonsmoker), history of myocardial infarction, history of angina, obesity (body mass index greater than 27.8 kg·m-2)(21), the general health rating index, resting ejection fraction (≤50%, >50%), months elapsed since qualifying cardiac event, and treatment assignment.
Fisher's exact test was used to compare the two treatment groups with respect to the proportions of patients whose achieved heart rate was within 5 beats·min-1 of their target heart rate. Analyses of covariance were performed to evaluate the effect of the following factors on the achieved heart rate at 6 months and 1 yr: resting ejection fraction, standing heart rate, and maximum exercise stage attained at the initial evaluation; exercise activity at enrollment; smoking status; alcohol use; history of myocardial infarction; history of angina; use of beta blockers; attendance at exercise sessions; and treatment assignment. To compare the achieved and target heart rates within each treatment group, the paired t-test was used.
Of the 197 patients, 87 were assigned to the low intensity program and 110 to the high intensity program. Most of the patients were white, married, worked fulltime, had undergone some post-high school education, were ex-smokers, and engaged in some exercise activities (Table 1). No more than 6 months had elapsed since the qualifying cardiac event for 59% of the patients, and the resting ejection fraction was greater than 50% for 65% of the patients. Forty-two of the patients had a history of myocardial infarction; 57% reported a history of angina(Table 2). The treatment groups were comparable with respect to demographic factors, medical history, and clinical characteristics.
Attendance at Exercise Sessions
The average monthly attendance rates for the low and high intensity groups were comparable in the first 6 months (Fig. 1). Overall, the average attendance rates in year 1 (mean ± SE) of 64.0% ± 2.5% in the low intensity group was higher than the 55.5% ± 2.7% in the high intensity groups, (P = 0.002). Attendance was lower in year 2 than in year 1 and a similar differential between the two treatment groups were observed. Not all factors associated with attendance were consistent between the two treatment groups. Older patients and those who were nonsmokers or ex-smokers were more likely to attend exercise sessions in both treatment groups (Table 3). Low intensity patients were more likely to attend exercise sessions if they worked full-time and if a short period of time had elapsed from their qualifying cardiac event. Among high intensity patients, a history of myocardial infarction and obesity were negatively associated with attendance. No relationship between the general health rating index and attendance was observed.
Achievement of Target Heart Rate
At 6 months, the target heart rate was achieved by 55% and 31% of the low and high intensity patients, respectively, a difference that was statistically significant (P = 0.003). At 1 yr, the proportion within the target range was essentially unchanged in the low intensity group (54%), but increased in the high intensity group (37%), and the difference was not statistically significant (P = 0.080). At both 6 months and 1 yr, treatment group, maximum stage achieved, and standing heart rate at initial evaluation were significantly associated with the achieved heart rate. None of the other factors including attendance at exercise sessions were associated with achieved heart rate.
Table 4 summarizes the target, achieved and difference between target and achieved heart rates. Although the achieved heart rates exceeded the targets in the low intensity group and fell short in the high intensity group, the differences between treatment groups with respect to achieved heart rate of 22.4 and 25.1 beats·min-1 at 6 months and 1 yr, respectively, were statistically significant. Among high intensity patients, the disparity between the achieved and target heart rates decreased from 6 months to 1 yr.
Lifestyle modifications require a long-term commitment from the patients, adequate social reinforcements, and attainable goals(14). Exercise adherence is related to the patient's perceived barriers to exercise and confidence in his ability to perform the exercise activity (5,17). As expected, attendance at exercise sessions in the TLC Trial declined with time. Attendance in both treatment groups was greater than previously reported among cardiac rehabilitation patients (4) and comparable to reports from other clinical trials (15). Since TLC participants were required to attend educational sessions prior to enrollment, they might be expected to demonstrate a high degree of adherence. The TLC attendance rates may be underestimated since no attempt was made to adjust for sessions that were missed involuntarily due to illness or other reasons. The lack of adjustment was intended to permit assessment of differential attendance between treatment groups, which may be related to the difficulty of the training program.
In the TLC Trial, patients were less likely to maintain attendance on the higher intensity program as has been previously reported(5,20). The two treatments differed only in intensity of exercise since the frequency and duration of sessions were the same in the two groups. In a 2-yr study of sedentary men and women between 50 and 65 yr of age and free of cardiovascular disease, adherence rates did not differ between the lower and higher intensity home-based exercise programs during the first year (7). In the second year, a lower adherence rate was observed in the lower intensity program(9), which may be due to the greater frequency of weekly sessions in the lower intensity program (five 30-min sessions) compared with the higher intensity program (three 60-min sessions)(9).
Intensity level is inversely related to exercise participation(6), but may be a greater factor in determining whether individuals adopt exercise. Since self-efficacy and perceived effort are associated with exercise adherence (6,8,17), the lower attendance rate in the higher intensity group may reflect the patients' lower self-confidence in their ability to perform this level of exercise. The finding that obesity and a history of myocardial infarction were negatively associated with attendance only for the high intensity group may reflect the physical limitations or perceived ability of patients with these attributes to perform at higher levels.
The finding that older patients were more likely to maintain an exercise session attendance rate necessary to receive therapeutic benefit corroborates other reports on exercise adherence (8) and clinic visit attendance (18,19). The higher attendance rate in older patients may reflect their greater concern for their health and their time availability. Cigarette smokers may be less committed to making lifestyle changes to improve their health and have been previously associated with poor adherence to exercise programs(2,8,15,16).
It was surprising to find that full-time work was positively associated with attendance in the low intensity group, but not in the high intensity group. Since full-time workers are likely to enjoy better overall health than other patients, this factor would be expected to have a positive effect on attendance in both groups. The negative association of attendance and time elapsed since the qualifying cardiac event corroborates previous findings that patients are more likely to change their behavior shortly after an event(14). The relationship of obesity and history of myocardial infarction with attendance in the high intensity group may reflect the physical limitations or perceived ability of this group of patients in participating at this level. Patients with these characteristics might have continued participation had they been assigned to the low intensity program.
Achievement of the target heart rate occured more frequently in the low intensity group than in the high intensity group, but was suboptimal for both groups. Although the target heart rates were infrequently achieved, a separation between the two intensity groups with respect to achieved heart rate was observed. Since the target was frequently exceeded in the low intensity group, the goal was realistic but may have been insufficiently demanding. The high intensity target, however, may have exceeded the capabilities of the patient population or may have been perceived as too challenging. A statistically significant separation was found between a lower and higher intensity home-based exercise programs with respect to the achieved heart rate at 1 yr (7). Similar to the TLC trial, participants assigned to the lower intensity level tended to achieve heart rates at the upper end of their target whereas higher intensity participants achieved heart rates toward the lower end of their target(7). The positive association between the standing heart rate and maximum exercise stage at the initial evaluation and achieved heart rate suggests that greater initial exercise capabilities positively influenced the ability to achieve a higher heart rate. The decrease in the difference between achieved and target heart rates observed in both treatment groups may reflect the additional benefit of exercise training among those who attended exercise sessions.
Because heart rate data were available only on attenders, the achieved heart rates reported here may be higher than in the total study population. Patients for whom data was not available were younger and more likely to be smokers than those whose data were included in the analysis, but these factors affected the two treatment groups similarly. The lack of heart rate data on the nonattenders may have contributed to the fact that no significant associations were detected between demographic factors and achieved heart rate.
Compared with other reports, higher attendance at the exercise sessions was observed in the TLC Trial, but was still disappointing. The low intensity program was preferable to achieve maximum attendance. Lower attendance on the high intensity program was associated with a history of myocardial infarction and obesity. These results suggest that to maximize the achieved heart rate, it would be optimal to motivate a cardiac rehabilitation patient to train at the high intensity level for a prolonged period of time.
Achieving and maintaining heart rates within the target ranges was difficult to achieve in both treatment groups. Low intensity patients were more likely to exceed their target heart rates and high intensity patients were more likely to fall short of their target heart rates. Nonetheless, significantly higher achieved heart rates were observed in the high intensity group compared to the low intensity group. Since variability in the achieved heart rate may be due to patient characteristics, physical exercise capacity and perceived ability to perform the prescribed exercise, exercise prescriptions should be tailored to individual preferences. Further research is needed to determine whether greater adherence and favorable outcomes can be attained by assigning patients to intervention based on their preference and aptitude.
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Keywords:©1996The American College of Sports Medicine
PATIENT COMPLIANCE; EXERCISE; CORONARY HEART DISEASE; CLINICAL TRIAL