Objective: Making lifestyle changes following a cardiac event to reduce cardiac risk factors, such as inactivity, is complex and difficult. Despite evidence that long-term exercise decreases morbidity and mortality following cardiac events, only 30 to 50% of individuals are exercising at six months after a cardiac event. Contemporary theories of health behavior change suggest that different factors influence the early adoption of an exercise regimen versus long-term adherence. Therefore, the purpose of this study was to determine the predictors of early exercise maintenance in individuals following a cardiac event.
Design: In this prospective longitudinal descriptive study, subjects were followed for three months after completion of a cardiac rehabilitation program.
Population and Sample: A convenience sample of sixty-four individuals (20 women and 44 men) having myocardial infarction, coronary artery bypass surgery or coronary angioplasty were consecutively recruited from three CR programs. The subject profile matched the national profile of participants in CR programs nationally. Subjects had a mean age of 62 (range=39-85), were predominately Caucasian (83%), had 14 years of education (range=10-20) and were married (69%).
Variables Studied: Three exercise variables constituted the dependent variables: (1) exercise frequency (# number of exercise sessions), (2) amount of exercise (total number of hours exercised over the study period), and (3) intensity (percent of time in target heart rate {THR} zone). Candidate predictor variables were physical variables (age, co-morbidity, cardiac functional status, fitness, muscle and joint pain while at rest or exercising, leg pain, anginal pain, and abdominal girth); psychosocial variables (social support, marital status, and depression); and cognitive variables (exercise benefits and barriers, exercise self-efficacy, motivation, and problem-solving skills). Only those variables significantly correlated with the respective dependent variables were included in the regression equations.
Methods: Consecutive subjects were approached for study participation near the completion of their CR program. Following written informed consent, data on the predictor variables were collected from chart review and a face-face 45-minute private interview using psychometrically sound instruments previously used with this population. Data on subject prescribed THR zones (adjusted for the use of heart rate attenuating medication) also were collected. Subjects were then given portable wristwatch heart rate (HR) monitors with programmed memory and instructed to wear them during exercise over the next 3 months. Monthly, data from the HR monitors were downloaded using a computer interface reader and tabular and graphic displays of the output exercise sessions were created. Stepwise linear regression was used to determine predictors of the three dimensions of exercise: frequency, amount, and intensity.
Findings: Nine individuals (14%) did no exercise following completion of CR. The mean number of exercise sessions per subject over the 12-week study period was 32 (S.D.=22), ranging from 0 to 96. The mean number of hours exercised was 29 (S.D.=22; range=0 - 96). The mean duration of an exercise session was 52 minutes (S.D.=21; range=10-112). The mean HR during an exercise session was 96 (S.D.=14.3; range=70-131). Subjects exercised within their target heart rate zone 33% of the time. When exercise frequency was regressed on the predictor variables, the overall model was significant (F(8,55)=3.6; p=.002 and accounted for 25% of the model variance, with exercise self-efficacy being the major independent predictor of exercise frequency. The overall model for exercise amount also was significant (F(5,58)=5.9; p=.000). Significant predictors of exercise amount were muscle and joint pain (t=-2.0; p=.05), lower leg pain (t=2.6; p=.01), self-efficacy (t=3.2; p=.002); and race (t=2.1; p=.04). The overall model for percent of time in THR zone was not significant, however, abdominal girth was a significant independent predictor, explaining 26% of the variance (t=-1.9; p=.05).
Conclusions: Despite the investment in a 12-week CR program, cardiac patients do not exercise at national recommended levels of frequency and intensity in the first three months after a program. Different dimensions of exercise were predicted by different factors, suggesting that different interventions may be needed to address the specific dimensions of exercise. Interventions should focus on self-efficacy enhancement; pain management for joint, muscle, and leg pain; and weight reduction.
Implications: Although CR programs are effective to recondition patients following cardiac events, improvement is needed in approaches to assist individuals to engage in a long-term exercise regimen. These data can be used to design more targeted and effective interventions to improve early exercise maintenance.
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