Journal of Behavioral Medicine, VoL. 15, No. 4, 1992
Adherence to Exercise Interventions in the Treatment of Hypercholesterolemia Denis J. Lynch, 1,7 Thomas J. Birk, 2 Michael T. Weaver, 3 Amira F. Gohara, 4 Richard F. Leighton, 5 Frank J. Repka, 1 and M. Eileen Walsh 6 Accepted for publication: August 30, 1991
The goals of this study were to determine the rate of adherence to exercise treatment of hypercholesterolemia and to identify personality and demographic factors associated with adherence. Of the 31 subjects entering the 26-week program, 12 attended 80% or more of the scheduled sessions. Adherence was positively associated with the perceived seriousness of hypercholesterolemia, the expectation of benefit from treatment, and depressed feelings of helplessness and hopelessness. Negative associations were identified between adherence and the perception of health status being under the control of chance or of powerful others. Older subjects were more likely to be adherers at 8 and 16 weeks but not at 26 weeks. KEY WORDS: adherence; exercise; hypercholesterolemia; personality.
INTRODUCTION The health risks associated with hypercholesterolemia have been known for some time and have led to intervention programs designed to reduce cholesterol levels. The risk of coronary heart disease in particular rises progressively with increased levels of cholesterol, especially at levels 1Department of Family Medicine, Medical College of Ohio, Toledo, Ohio 43699-9988. 2Department of Rehabilitation Medicine, Medical College of Ohio, Toledo, Ohio 43699-9988. 3Department of Obstetrics and Gynecology, Medical College of Ohio, Toledo, Ohio 43699-9988. 4Department of Pathology, Medical College of Ohio, Toledo, Ohio 43699-9988. SDepartment of Medicine, Medical College of Ohio, Toledo, Ohio 43699-9988. 6School of Nursing, Medical College of Ohio, Toledo, Ohio 43699-9988. 7To whom correspondence should be addressed. 365
0160-7715/92/0800-0365506.50109 1992PlenumPublishingCorporation
366
Lynch et al.
greater than 200 mg/dl (National Cholesterol Panel, 1988). More detailed evaluations and possible interventions are generally recommended for patients with levels of 240 mg/dl. More than 50% of American men and women 45 or older have cholesterol levels of 220 mg/dl or greater, and more than 25% have levels greater than 240 mg/dl (National Center for Health Statistics, 1986). Clearly this is a health problem prevalent enough to merit attention. Further, the benefit of reducing cholesterol levels also argues for active intervention. When initial serum cholesterol levels are in the range of 250-300 mg/dl, each 1% reduction in cholesterol level is associated with a 2-3% reduction in rate of coronary heart disease (Lipid Research Clinics Progran, 1984b; Sleight, 1991). With the identification of health risks associated with hypercholesterolemia, interventions have been developed to treat this condition. While these interventions have most often taken the form of diet modification (Lipid Research Clinics, 1984a; Schulman et al., 1990) and medication, exercise programs have also been identified as a way of lowering cholesterol levels (National Cholesterol Panel, 1988; Stein et al., 1990; Keleman et al., 1990). Williams and his associates (1990) have demonstrated that either diet or exercise programs can lead to significant improvement in lipoprotein profiles in a group of sendentary men. Since interventions to lower cholesterol levels have only recently been instituted, little is known about rates of adherence to recommended treatments (Neale et al., 1989; Lynch et al., 1988). Information regarding adherence rates would help us to understand whether patients are willing to accept prevention programs; in addition, it would be helpful to know if adherence to prevention programs can be predicted from demographic or personality variables. Adherence to medical recommendations has been an extensively studied problem (Haynes et al., 1979). These studies are necessary given that adherence rates have frequently been found to be disappointingly low (Sackett and Snow, 1979), and poor adherence can result in longer periods of illness, serious complications, and higher relapse rates (Kaplan and Simon, 1990). In past studies, various factors, especially situational and demographic variables, have been studied in relationship to adherence (Dishman, 1982).
Situational Factors
Situational factors include the degree of inconvenience or discomfort experienced by the patient in undertaking the recommended treatment
Adherence to Exercise Interventions in
Hypercholesterolemia
367
(Andrew et al., 1981). Further, patients appear to be less willing to cooperate when they are currently experiencing little or no distress related to the condition (Dishman, 1982; Haynes et al., 1979). Studies on pill taking for hypertension illustrate that adherence for asymptomatic conditions is lower than when the medical problem is associated with troubling or painful symptoms (Sackett et al., 1976). Cost to the patient of the treatment represents another situational factor that may be associated with adherence. Cost in this case might be financial but more often includes time, pain, or inconvenience associated with the treatment. Exercise programs, in particular, demand significant expenditures of time and effort and are associated with low adherence rates (Oldridge, 1982; Dishman, 1982). Demographic Factors
Demographic factors such as age, education, and gender have been evaluated in relationship to adherence (Sallis and Hovel, 1990). In reviewing studies that considered the relationship of age to adherence, Dishman and his associates (1985) reported that no associations had been found. However, Ward and Morgan (1984) reported, in their study of exercise adherence, that adherers tended to be older than dropouts. A small but positive association between education and adherence has been reported (Dishman et al., 1985). Early studies focused only on males, and so little is known about gender differences in adherence (Oldridge, 1982). However it appears that adherence rates for males and females may not be significantly different (Ward and Morgan, 1984). Miscellaneous Factors
A variety of personality and interpersonal factors has been examined in regard to adherence (Sonstroem, 1988). Both emotional states, such as anxiety and depression, and cognitively based factors, such as attitudes about health, have been considered. For example, patients' perceptions regarding the seriousness of their health status are factors incorporated into the health belief model as it is applied to adherence (Becker and Maiman, 1975). Similarly the patients' conception of the source of control over their health status (e.g., chance factors) has been found to be associated with adherence (Wallstrom et al., 1978). In the interpersonal area, perceived social support has been investigated as it relates to adherence to medical recommendations. A positive attitude toward the exercise program by one's spouse has been found to be associated with better adherence (Dishman, 1982; Oldridge, 1982). In addition, social reinforcement from exercise part-
368
Lynch et al.
ners and program staff can also strengthen adherence (Mann et al., 1969; Dishman et al., 1985). Although there is increasing public awareness about the health risks associated with hypercholesterolemia, preventive intervention programs are still being developed, and it is not clear whether patients will be responsive to such programs. Besides evaluating the rate of adherence to prevention programs, knowledge of personality and demographic factors associated with adherence will help us to understand better which patients may require extra attention to increase their participation in prevention programs. The goals of the present study were (1) to determine the rate of adherence to a serum cholesterol-reducing exercise program and (2) to identify factors associated with adherence to such a program.
METHODS Subject Selection Initially, 1024 nonfasting subjects, who were either faculty, students, or staff at a medical college, were screened for determination of total serum cholesterol using blood secured via venipuncture (Leighton et al., 1990). Subsequently, 396 subjects, whose total serum cholesterol values exceeded the cutoff points for age recommended by the NIH Consensus Conference (1985), were asked to return for two fasting serum lipid profiles. Fasting lipid values were averaged for each of the 304 subjects who returned for both determinations. Subjects were further considered for inclusion in the study if their serum low-density lipoprotein (LDL)-cholesterol value exceeded the Lipid Research Center (LRC) 75th percentile for age and gender and if their triglycerides were less than 400 mg/dl. Subjects who met these criteria were invited to return for interviews to determine further eligibility for the study. Subjects with marked obesity, histories of heart, liver, thyroid, pulmonary or renal disease, and chest pain consistent with angina pectoris were excluded. Individuals with hypertension or diabetes mellitis were excluded if they required drug therapy. Also excluded were subjects who were above average aerobic capacity for gender and age standards. From 93 eligible subjects, 66 consented and 33 were randomly assigned to the aerobic exercise treatment program. The mean age was 40.5 years and the standard deviation was 11.3 (see Table I). Of these 33 subjects, nine were male. Three of the subjects were African-American and the rest were Caucasian.
Adherence to Exercise Interventions in
Hypercholesterolemla
369
Table I. Descriptive Statistics for Significant Study Variables
Variable Depression (MBHI) Health Belief Seriousness Benefit HLC Chance Powerful Others Age
,X
SD
6.7
4.2
Minimum 1.0
Maximum 22.0
4.4 8.9
0.8 1.1
3.0 6.0
5.0 10.0
18.0 14.5 40.5
6.0 4.3 11.3
6.0 7.0 26.0
30.0 24.0 68.0
Assessments
Prior to beginning the exercise treatment program, each subject completed the following behavioral questionnaires. MiUon BehavioralHealth Inventory (MBHI) (MiUon et al., 1982). This is a 150 item true/false test. Norms are based on groups of general medical patients as well as nonclinical subjects. From responses made, 20 scales are derived which are grouped into four broad categories: basic coping styles, psychogenic attitudes, psychosomatic correlates, and prognostic indexes. Although the entire inventory was administered, only the Cooperative, Confident, Chronic Tension, Premorbid Pessimism, and Recent Stress scales were hypothesized to be associated with adherence behaviors. Health Locus of Control Scale (I-ILC) (Wallstrom et al., 1976, 1978). This is an 18-item Likert-type scale designed to tap an individual's perceptions of the source of control of their health status (self, chance, or powerful others). Jenkins Activity Survey (JAS) (Jenkins et al., 1974). This test was developed as a paper-and-pencil alternative to the structured interview method from which the Type A or coronary prone personality was diagnosed. It consists of 52 items, and four scales are derived from the scale: the Type A Scale (assessing a multifactorial construct of coronary proneness), as well as three factorily independent components of the broader construct (the speed and impatience subscale, the job-involvement subscale, and the hard-driving and competitive subscale). Self Motivation Inventory (SMI) (Dishman et al., 1980). This is a 40item self-report scale developed to assess self-motivation, especially in an exercise activity. Sarason Social Support Scale (SSSI) (Sarason et al, 1983). This is a self-report measure, consisting of 54 items and yielding two specific scores:
370
Lynch et al.
number of social supports and degree of satisfaction with available social support.
Eleven Liken-Type Items Constructed to Determine Health Beliefs Regarding Hypercholesterolemia (HBI) (Becker and Maiman, 1975). Following the compoents of this model, these items attempted to measure each subject's (a) perception of the severity of hypercholesterolemia, (b) perceived susceptability to effects of hypercholesterolemia, and (c) perceptions of the benefit of an exercise program in reducing his/her cholesterol level (e.g., "How beneficial do you think changing your exercise patterns would be in lowering your blood cholesterol level?"). Aerobic capacity was also assessed by measuring maximal oxygen consumption (max VO2). Max VO2 was determined by gas analysis with opencircuit spirometry during a graduated treadmill exercise test. The subjects' heart rates and electrocardiograms were constantly monitored and recorded at minute intervals. Blood pressure and an undifferentiated rate of perceived exertion were determined at each 3-min work stage interval. The protocol was terminated when there was a leveling off of max VO2 or heart rate with an increasing workload, a respiratory exchange rate greater than 1.1, or a rate of perceived exertion greater than 17 or "very hard."
Aerobic Exercise Treatment Program The exercise treatment program entailed 26 weeks of supervised aerobic exercise on stationary and combined leg-arm ergometer bicycles, walking/jogging, stair-climbing, and rowing. Subjects reported for supervised exercise treatment 3 alternative days/week in small groups. Although in small groups, each subject was performing at an individualized intensity and duration as prescribed from the preevaluation. Since all subjects were average or less in aerobic capacity, early sessions were designed to increase in intensity and duration in a gradual manner. During the initial sessions of the first 10 weeks, a duration of 25 min was used with an intensity of 60% of heart rate reserve or 55% of max VO2. At the end of the 10-week "preconditioning" period, the duration was at approximately 45 min for most subjects and up to a 80% of heart rate reserve or 75% of VO2 max intensity. The subjects remained at this level for the remaining 16 weeks of the 26-week study. All subjects were required to warm up adequately for 5-10 rain with a combination of exercises designed to increase heart rate and metabolism to the prescribed intensity. Cool-down exercises at the end of each treatment session consisted of slow-moving, whole-body-type exercises, such as
Adherence to Exercise Interventions in
Hypercholesterolemia
371
walking for 5 min. This was followed by static stretching of the major muscle groups.
Analysis The measurement of adherence for this study was approached in two ways. (1) Subjects who attended 80% or more of scheduled exercise sessions were considered adherers, whereas those who attended less than 80% of scheduled sessions were considered nonadherers. This cutoff was based on the level of exercise frequency needed to achieve health benefits from the exercises (Oldridge, 1982). (2) Adherence was also expressed as a continuous variable (the percentage of exercise sessions attended). The additional approach was used to include another perspective on adherence behavior. With three sessions scheduled for each of the 26 weeks, a total of 78 sessions should have been attended. Although it was expected that these two measurers of adherence would correlate highly with one another, it was felt that there would be value in retaining both. The first approach, which dichotomized subjects, would have practical value since the dividing point was based on the level of activity needed for health benefits, and adherence levels below this point would probably not result in the desired therapeutic effect. By also using the continuous measure, more of the data would be used and might give us additional information about the relationship between the predictor variables and adherence. Polyserial correlations (Ioreskog and Sorbom, 1988) were calculated between the dichotomized attendance variable and the personality and demographic data gathered from the questionnaires, while Pearson product-moment correlations were calculated between the percentage of sessions attended and the personality and demographic data. Because of the large number of correlations evaluated, only correlations of 0.40 or greater were considered important for indicating an association between personality or demographic variables and the adherence measures.
RESULTS Although 33 subjects were assigned to the exercise program, data were available for only 31 subjects. (The missing data were due to random errors rather than adherence problems.) Of these 31 subjects, 20 (or 65%)
372
Lynch et al.
had attended 80% or more of the sessions at 8 weeks into the program, 14 (or 45%) at 16 weeks, and 12 (or 39%) at the end of the sessions (26 weeks). A declining trend in number of adherers over the 26 weeks was thus detected and is shown in Fig. 1. The median percentage of sessions attended at the 8-, 16-, and 26-week points were 92, 81, and 76%, respectively. Items tapping health beliefs regarding hypercholesterolemia were found to be associated with adherence. More specifically, subjects reporting a higher expectation of benefit from an exercise program were more likely to be categorized as adherers (attending 80% or more of scheduled sessions) at 8 weeks (r = .40, p < .05), at 16 weeks (r = .49, p < .01), and at the end of the 26 week program (r = .40, p < .05). Belief in the seriousness of the health risks associated with hyopercholesterolemia was also associated with adherence. Adherence status at 26 weeks (r = 0.45, p < .02) and percentage of sessions attended (r = 0.50, p < .01) were both associated with health beliefs regarding the seriousness of hypercholesterolemia. On the HLC, both the "powerful others" subscale (r = -.56, p < .01) and the "chance" subscale (r = -.43, p < .02) were inversely related
I~176 I 901 ............................................................................................................................. 80
................................................................................................................................
70 ...................................................................................................................................................... O) .C
.
Adherence to Exercise Interventions in the Treatment of Hypercholesterolemia Denis J. Lynch, 1,7 Thomas J. Birk, 2 Michael T. Weaver, 3 Amira F. Gohara, 4 Richard F. Leighton, 5 Frank J. Repka, 1 and M. Eileen Walsh 6 Accepted for publication: August 30, 1991
The goals of this study were to determine the rate of adherence to exercise treatment of hypercholesterolemia and to identify personality and demographic factors associated with adherence. Of the 31 subjects entering the 26-week program, 12 attended 80% or more of the scheduled sessions. Adherence was positively associated with the perceived seriousness of hypercholesterolemia, the expectation of benefit from treatment, and depressed feelings of helplessness and hopelessness. Negative associations were identified between adherence and the perception of health status being under the control of chance or of powerful others. Older subjects were more likely to be adherers at 8 and 16 weeks but not at 26 weeks. KEY WORDS: adherence; exercise; hypercholesterolemia; personality.
INTRODUCTION The health risks associated with hypercholesterolemia have been known for some time and have led to intervention programs designed to reduce cholesterol levels. The risk of coronary heart disease in particular rises progressively with increased levels of cholesterol, especially at levels 1Department of Family Medicine, Medical College of Ohio, Toledo, Ohio 43699-9988. 2Department of Rehabilitation Medicine, Medical College of Ohio, Toledo, Ohio 43699-9988. 3Department of Obstetrics and Gynecology, Medical College of Ohio, Toledo, Ohio 43699-9988. 4Department of Pathology, Medical College of Ohio, Toledo, Ohio 43699-9988. SDepartment of Medicine, Medical College of Ohio, Toledo, Ohio 43699-9988. 6School of Nursing, Medical College of Ohio, Toledo, Ohio 43699-9988. 7To whom correspondence should be addressed. 365
0160-7715/92/0800-0365506.50109 1992PlenumPublishingCorporation
366
Lynch et al.
greater than 200 mg/dl (National Cholesterol Panel, 1988). More detailed evaluations and possible interventions are generally recommended for patients with levels of 240 mg/dl. More than 50% of American men and women 45 or older have cholesterol levels of 220 mg/dl or greater, and more than 25% have levels greater than 240 mg/dl (National Center for Health Statistics, 1986). Clearly this is a health problem prevalent enough to merit attention. Further, the benefit of reducing cholesterol levels also argues for active intervention. When initial serum cholesterol levels are in the range of 250-300 mg/dl, each 1% reduction in cholesterol level is associated with a 2-3% reduction in rate of coronary heart disease (Lipid Research Clinics Progran, 1984b; Sleight, 1991). With the identification of health risks associated with hypercholesterolemia, interventions have been developed to treat this condition. While these interventions have most often taken the form of diet modification (Lipid Research Clinics, 1984a; Schulman et al., 1990) and medication, exercise programs have also been identified as a way of lowering cholesterol levels (National Cholesterol Panel, 1988; Stein et al., 1990; Keleman et al., 1990). Williams and his associates (1990) have demonstrated that either diet or exercise programs can lead to significant improvement in lipoprotein profiles in a group of sendentary men. Since interventions to lower cholesterol levels have only recently been instituted, little is known about rates of adherence to recommended treatments (Neale et al., 1989; Lynch et al., 1988). Information regarding adherence rates would help us to understand whether patients are willing to accept prevention programs; in addition, it would be helpful to know if adherence to prevention programs can be predicted from demographic or personality variables. Adherence to medical recommendations has been an extensively studied problem (Haynes et al., 1979). These studies are necessary given that adherence rates have frequently been found to be disappointingly low (Sackett and Snow, 1979), and poor adherence can result in longer periods of illness, serious complications, and higher relapse rates (Kaplan and Simon, 1990). In past studies, various factors, especially situational and demographic variables, have been studied in relationship to adherence (Dishman, 1982).
Situational Factors
Situational factors include the degree of inconvenience or discomfort experienced by the patient in undertaking the recommended treatment
Adherence to Exercise Interventions in
Hypercholesterolemia
367
(Andrew et al., 1981). Further, patients appear to be less willing to cooperate when they are currently experiencing little or no distress related to the condition (Dishman, 1982; Haynes et al., 1979). Studies on pill taking for hypertension illustrate that adherence for asymptomatic conditions is lower than when the medical problem is associated with troubling or painful symptoms (Sackett et al., 1976). Cost to the patient of the treatment represents another situational factor that may be associated with adherence. Cost in this case might be financial but more often includes time, pain, or inconvenience associated with the treatment. Exercise programs, in particular, demand significant expenditures of time and effort and are associated with low adherence rates (Oldridge, 1982; Dishman, 1982). Demographic Factors
Demographic factors such as age, education, and gender have been evaluated in relationship to adherence (Sallis and Hovel, 1990). In reviewing studies that considered the relationship of age to adherence, Dishman and his associates (1985) reported that no associations had been found. However, Ward and Morgan (1984) reported, in their study of exercise adherence, that adherers tended to be older than dropouts. A small but positive association between education and adherence has been reported (Dishman et al., 1985). Early studies focused only on males, and so little is known about gender differences in adherence (Oldridge, 1982). However it appears that adherence rates for males and females may not be significantly different (Ward and Morgan, 1984). Miscellaneous Factors
A variety of personality and interpersonal factors has been examined in regard to adherence (Sonstroem, 1988). Both emotional states, such as anxiety and depression, and cognitively based factors, such as attitudes about health, have been considered. For example, patients' perceptions regarding the seriousness of their health status are factors incorporated into the health belief model as it is applied to adherence (Becker and Maiman, 1975). Similarly the patients' conception of the source of control over their health status (e.g., chance factors) has been found to be associated with adherence (Wallstrom et al., 1978). In the interpersonal area, perceived social support has been investigated as it relates to adherence to medical recommendations. A positive attitude toward the exercise program by one's spouse has been found to be associated with better adherence (Dishman, 1982; Oldridge, 1982). In addition, social reinforcement from exercise part-
368
Lynch et al.
ners and program staff can also strengthen adherence (Mann et al., 1969; Dishman et al., 1985). Although there is increasing public awareness about the health risks associated with hypercholesterolemia, preventive intervention programs are still being developed, and it is not clear whether patients will be responsive to such programs. Besides evaluating the rate of adherence to prevention programs, knowledge of personality and demographic factors associated with adherence will help us to understand better which patients may require extra attention to increase their participation in prevention programs. The goals of the present study were (1) to determine the rate of adherence to a serum cholesterol-reducing exercise program and (2) to identify factors associated with adherence to such a program.
METHODS Subject Selection Initially, 1024 nonfasting subjects, who were either faculty, students, or staff at a medical college, were screened for determination of total serum cholesterol using blood secured via venipuncture (Leighton et al., 1990). Subsequently, 396 subjects, whose total serum cholesterol values exceeded the cutoff points for age recommended by the NIH Consensus Conference (1985), were asked to return for two fasting serum lipid profiles. Fasting lipid values were averaged for each of the 304 subjects who returned for both determinations. Subjects were further considered for inclusion in the study if their serum low-density lipoprotein (LDL)-cholesterol value exceeded the Lipid Research Center (LRC) 75th percentile for age and gender and if their triglycerides were less than 400 mg/dl. Subjects who met these criteria were invited to return for interviews to determine further eligibility for the study. Subjects with marked obesity, histories of heart, liver, thyroid, pulmonary or renal disease, and chest pain consistent with angina pectoris were excluded. Individuals with hypertension or diabetes mellitis were excluded if they required drug therapy. Also excluded were subjects who were above average aerobic capacity for gender and age standards. From 93 eligible subjects, 66 consented and 33 were randomly assigned to the aerobic exercise treatment program. The mean age was 40.5 years and the standard deviation was 11.3 (see Table I). Of these 33 subjects, nine were male. Three of the subjects were African-American and the rest were Caucasian.
Adherence to Exercise Interventions in
Hypercholesterolemla
369
Table I. Descriptive Statistics for Significant Study Variables
Variable Depression (MBHI) Health Belief Seriousness Benefit HLC Chance Powerful Others Age
,X
SD
6.7
4.2
Minimum 1.0
Maximum 22.0
4.4 8.9
0.8 1.1
3.0 6.0
5.0 10.0
18.0 14.5 40.5
6.0 4.3 11.3
6.0 7.0 26.0
30.0 24.0 68.0
Assessments
Prior to beginning the exercise treatment program, each subject completed the following behavioral questionnaires. MiUon BehavioralHealth Inventory (MBHI) (MiUon et al., 1982). This is a 150 item true/false test. Norms are based on groups of general medical patients as well as nonclinical subjects. From responses made, 20 scales are derived which are grouped into four broad categories: basic coping styles, psychogenic attitudes, psychosomatic correlates, and prognostic indexes. Although the entire inventory was administered, only the Cooperative, Confident, Chronic Tension, Premorbid Pessimism, and Recent Stress scales were hypothesized to be associated with adherence behaviors. Health Locus of Control Scale (I-ILC) (Wallstrom et al., 1976, 1978). This is an 18-item Likert-type scale designed to tap an individual's perceptions of the source of control of their health status (self, chance, or powerful others). Jenkins Activity Survey (JAS) (Jenkins et al., 1974). This test was developed as a paper-and-pencil alternative to the structured interview method from which the Type A or coronary prone personality was diagnosed. It consists of 52 items, and four scales are derived from the scale: the Type A Scale (assessing a multifactorial construct of coronary proneness), as well as three factorily independent components of the broader construct (the speed and impatience subscale, the job-involvement subscale, and the hard-driving and competitive subscale). Self Motivation Inventory (SMI) (Dishman et al., 1980). This is a 40item self-report scale developed to assess self-motivation, especially in an exercise activity. Sarason Social Support Scale (SSSI) (Sarason et al, 1983). This is a self-report measure, consisting of 54 items and yielding two specific scores:
370
Lynch et al.
number of social supports and degree of satisfaction with available social support.
Eleven Liken-Type Items Constructed to Determine Health Beliefs Regarding Hypercholesterolemia (HBI) (Becker and Maiman, 1975). Following the compoents of this model, these items attempted to measure each subject's (a) perception of the severity of hypercholesterolemia, (b) perceived susceptability to effects of hypercholesterolemia, and (c) perceptions of the benefit of an exercise program in reducing his/her cholesterol level (e.g., "How beneficial do you think changing your exercise patterns would be in lowering your blood cholesterol level?"). Aerobic capacity was also assessed by measuring maximal oxygen consumption (max VO2). Max VO2 was determined by gas analysis with opencircuit spirometry during a graduated treadmill exercise test. The subjects' heart rates and electrocardiograms were constantly monitored and recorded at minute intervals. Blood pressure and an undifferentiated rate of perceived exertion were determined at each 3-min work stage interval. The protocol was terminated when there was a leveling off of max VO2 or heart rate with an increasing workload, a respiratory exchange rate greater than 1.1, or a rate of perceived exertion greater than 17 or "very hard."
Aerobic Exercise Treatment Program The exercise treatment program entailed 26 weeks of supervised aerobic exercise on stationary and combined leg-arm ergometer bicycles, walking/jogging, stair-climbing, and rowing. Subjects reported for supervised exercise treatment 3 alternative days/week in small groups. Although in small groups, each subject was performing at an individualized intensity and duration as prescribed from the preevaluation. Since all subjects were average or less in aerobic capacity, early sessions were designed to increase in intensity and duration in a gradual manner. During the initial sessions of the first 10 weeks, a duration of 25 min was used with an intensity of 60% of heart rate reserve or 55% of max VO2. At the end of the 10-week "preconditioning" period, the duration was at approximately 45 min for most subjects and up to a 80% of heart rate reserve or 75% of VO2 max intensity. The subjects remained at this level for the remaining 16 weeks of the 26-week study. All subjects were required to warm up adequately for 5-10 rain with a combination of exercises designed to increase heart rate and metabolism to the prescribed intensity. Cool-down exercises at the end of each treatment session consisted of slow-moving, whole-body-type exercises, such as
Adherence to Exercise Interventions in
Hypercholesterolemia
371
walking for 5 min. This was followed by static stretching of the major muscle groups.
Analysis The measurement of adherence for this study was approached in two ways. (1) Subjects who attended 80% or more of scheduled exercise sessions were considered adherers, whereas those who attended less than 80% of scheduled sessions were considered nonadherers. This cutoff was based on the level of exercise frequency needed to achieve health benefits from the exercises (Oldridge, 1982). (2) Adherence was also expressed as a continuous variable (the percentage of exercise sessions attended). The additional approach was used to include another perspective on adherence behavior. With three sessions scheduled for each of the 26 weeks, a total of 78 sessions should have been attended. Although it was expected that these two measurers of adherence would correlate highly with one another, it was felt that there would be value in retaining both. The first approach, which dichotomized subjects, would have practical value since the dividing point was based on the level of activity needed for health benefits, and adherence levels below this point would probably not result in the desired therapeutic effect. By also using the continuous measure, more of the data would be used and might give us additional information about the relationship between the predictor variables and adherence. Polyserial correlations (Ioreskog and Sorbom, 1988) were calculated between the dichotomized attendance variable and the personality and demographic data gathered from the questionnaires, while Pearson product-moment correlations were calculated between the percentage of sessions attended and the personality and demographic data. Because of the large number of correlations evaluated, only correlations of 0.40 or greater were considered important for indicating an association between personality or demographic variables and the adherence measures.
RESULTS Although 33 subjects were assigned to the exercise program, data were available for only 31 subjects. (The missing data were due to random errors rather than adherence problems.) Of these 31 subjects, 20 (or 65%)
372
Lynch et al.
had attended 80% or more of the sessions at 8 weeks into the program, 14 (or 45%) at 16 weeks, and 12 (or 39%) at the end of the sessions (26 weeks). A declining trend in number of adherers over the 26 weeks was thus detected and is shown in Fig. 1. The median percentage of sessions attended at the 8-, 16-, and 26-week points were 92, 81, and 76%, respectively. Items tapping health beliefs regarding hypercholesterolemia were found to be associated with adherence. More specifically, subjects reporting a higher expectation of benefit from an exercise program were more likely to be categorized as adherers (attending 80% or more of scheduled sessions) at 8 weeks (r = .40, p < .05), at 16 weeks (r = .49, p < .01), and at the end of the 26 week program (r = .40, p < .05). Belief in the seriousness of the health risks associated with hyopercholesterolemia was also associated with adherence. Adherence status at 26 weeks (r = 0.45, p < .02) and percentage of sessions attended (r = 0.50, p < .01) were both associated with health beliefs regarding the seriousness of hypercholesterolemia. On the HLC, both the "powerful others" subscale (r = -.56, p < .01) and the "chance" subscale (r = -.43, p < .02) were inversely related
I~176 I 901 ............................................................................................................................. 80
................................................................................................................................
70 ...................................................................................................................................................... O) .C
.
