Physical inactivity and low cardiorespiratory fitness are recognized as important causes of morbidity and mortality in industrialized countries (35,42). The strength of the association between inactivity and ill health and its high prevalence in these societies leads to a substantial population burden for sedentary behavior. In the United States, as much as one-third of the deaths from coronary heart disease, type II diabetes, and colon cancer may result from insufficient physical activity (37). Hahn and colleagues estimate that approximately 250,000 deaths per year can be attributed to physical inactivity (17). These data underestimate the total burden of inactivity because they do not account for loss of function and other nonfatal health problems caused by low levels of physical fitness in elderly men and women.
Since the mid-1980s, the prevalence of American adults who are regularly physically active at levels sufficient to reduce their risk of all-cause mortality and cardiovascular disease has not increased, and approximately 60% of the adult U.S. population remain inadequately active with 25% reporting no activity (42). The magnitude of the public health burden of sedentary lifestyles led the U.S. Public Health Service to include activity and fitness in national health objectives (34). A joint statement on physical activity and public health from the Centers for Disease Control and Prevention and the American College of Sports Medicine (36), a recent National Institutes of Health consensus development conference on physical activity and cardiovascular health (35), and the U.S. Surgeon General's Report on Physical Activity and Health (42) call attention to the importance of a physically active way of life.
Various public health, scientific, and medical groups currently promote physical activity, but advice and education alone are not sufficient to produce significant increases in the adoption of regular physical activity (10). The predominant model for increasing physical activity behavior has targeted individuals in a group or gymnasium-based program using exercise prescription guidelines of frequency, intensity, and duration of exercise developed and promulgated by the American College of Sports Medicine (1). The need for alternatives to structured exercise led us to develop a lifestyle physical activity approach (3,6). This approach encourages integration of more physical activity over the course of the day by increasing short sessions of walking or stair climbing and by seeking and creating opportunities for short bouts of moderate intensity activities during the course of one's daily life. It also emphasizes increasing motivational readiness and cognitive and behavioral skill building based on the Stages of Motivational Readiness model of behavior change (38) and Social Cognitive Theory (2). The purpose of this report is to present data on changes in physical activity and cardiorespiratory fitness over the course of 6 months of systematic intensive intervention using both structured and lifestyle approaches in a randomized clinical trial in a group of initially sedentary men and women. A subsequent paper will report on the changes over 24 months. The primary hypothesis under investigation was that both structured and lifestyle groups would significantly increase their physical activity and cardiorespiratory fitness at the end of 6 months compared with baseline.
Participants and design. Project Active is a randomized clinical trial designed to evaluate two different physical activity interventions. The design is similar to other clinical trials in medicine where a new treatment (lifestyle) is compared with a standard (structured) treatment. Participants assigned to structured exercise engaged in supervised exercise at a well equipped fitness center. Participants assigned to the lifestyle group participated in a behavioral, group process intervention designed to help them integrate more physical activity into their daily routines. The study design was for 6 months of intensive intervention with 18 months of follow-up intervention.
Two-hundred thirty-five healthy but sedentary men (N = 116) and women (N = 119) aged 35 to 60 who lived or worked within a 10-mile radius of our center were recruited in three separate cohorts at 6-month intervals. Ethnic composition of this sample was 73% nonhispanic Caucasian, 14% African American, 12% Mexican American, and 1% other. The mean educational level was 16 yr, and over two-thirds of all participants were married. Almost 88% were employed full-time, 3% were housewives, 6% were employed part-time, and 3% were unemployed or semi- or fully retired. Written consent was obtained from all participants in accordance with the policy statement regarding the use of human subjects and informed consent for the American College of Sports Medicine. The study protocol was approved annually by the Institutional Review Board at The Cooper Institute for Aerobics Research. Written informed consent was obtained from each participant before initiating testing procedures and again before randomization. Further detail on methods is described by Kohl et al. (24).
Participants were screened and excluded for the following: 1. a self-reported history of myocardial infarction, stroke, insulin-dependent diabetes mellitus, osteoporosis, or osteoarthritis (if it limited mobility); 2. exceeded 140% of ideal body weight; 3. plan to move from the local area within the time span of the study; 4. consume five or more drinks of alcohol a day; 5. physical activity at least 3 d·wk−1 for 20 min or more each time, or an estimated total energy expenditure exceeding 36 kcal·kg−1·d−1 (men) or 34 kcal·kg−1·d−1 (women) as measured by the 7-Day Physical Activity Recall (PAR) (5); 6. systolic blood pressure ≥160 mm Hg or diastolic blood pressure ≥100 mm Hg; 7. take medications such as β-blockers that could impair exercise performance; and 8. for women, plan to become pregnant in the next 2 yr.
Clinical measurements. All measurements are described in detail elsewhere (24). Briefly, following an initial telephone screening, eligible participants completed a PAR and medical history at a study orientation session. If they remained eligible following review of these data, participants were scheduled for a physical examination and clinical assessments including resting blood pressure measurements (16) and individual PAR interviews (5). Those continuing to meet eligibility criteria were scheduled for a second laboratory examination for anthropometry and a maximal exercise test (7) with oxygen uptake measured with automated cardiorespiratory monitoring techniques. All treadmill tests were performed to determine peak oxygen uptake. This was confirmed by a plateau in oxygen consumption with an increasing work rate, a respiratory exchange ratio greater than or equal to 1.15 and a maximum heart rate within 10 beats·min−1 of the participant's age-predicted maximum, or physical exhaustion during the test. The test also included measurement of resting and exercise electrocardiograms and blood pressures. Body fat was estimated from 7-site skin-fold measurements (18,19). Within 6 wk of completion of baseline testing, the entire cohort was randomized into lifestyle or structured groups. Randomization was balanced to equalize the number of men and women in each of the intervention groups (14). All measures obtained at baseline also were completed after 6 months of intervention.
Outcome measures. The primary outcome measure used to assess changes in physical activity was total energy expenditure (kcal·kg−1·d−1), as estimated by the PAR. This measure includes energy expenditure from moderate activities, hard activities, and very hard activities. Additional physical activity questions probed for the number of hours spent sitting per day, number of minutes spent walking per day, pace of walking (e.g., casual or strolling, average or normal, fairly brisk or brisk or striding), and flights of stairs climbed per day. The primary outcome measure used to assess changes in cardiorespiratory fitness was peak V˙O2 (mL·kg−1·min−1). Secondary measures of cardiorespiratory fitness were total treadmill time (min) and heart rate (beats·min−1) at a specified submaximal stage of the Bruce protocol graded exercise test (8).
Intervention. Interventions used in Project Active are described elsewhere (12,24). To summarize, the guiding theoretical framework for both interventions was the stages of motivational readiness model (38) and social cognitive theory (2). The stages of motivational readiness model as applied to physical activity behavior (31) proposes that individuals differ in their readiness for adoption of regular physical activity. Individuals are classified as being in 1. precontemplation: not intending to change; 2. contemplation: intending to change; 3. preparation: making small changes; 4. action: meeting behavior change criteria (in this case, meeting the CDC/ACSM physical activity recommendation for public health); or 5. maintenance: sustaining the change in behavior over time (e.g., 6 months or more). In the study design, physical activity and fitness goals for the first 6 months were to increase activity by 3 kcal·kg−1·d−1 and to increase cardiorespiratory fitness by 5 mL·kg−1·min−1 for both intervention groups.
For the 6 months of intensive intervention, participants randomized to the structured group received a free membership to the Cooper Fitness Center, a state-of-the-art health club with extensive services, equipment, facilities, and programs. A trained exercise leader provided each participant with an ACSM exercise prescription (1), and participants were asked to exercise at the Center under the leader's supervision at least 30 min a day, 3 d·wk−1. This leader was on site 3 h in the morning and 3 h in the afternoon, Monday through Friday. As fitness improved, participants progressed to exercising 5 d·wk−1. The exercise leader contacted any participant who failed to attend at least 1 session per wk, and these participants were encouraged to return to a program of regularly scheduled exercise as soon as possible. All participants began their program by walking, but at the end of 3 wk they were allowed to choose any alternative aerobic exercise at the fitness center. The exercise leader helped participants set realistic physical activity goals and taught them how to monitor their physical activity by logging exercise bouts into a computerized system that is part of the fitness center service. Verbal reinforcement was given for meeting short- and long-term goals. We encouraged participants to become self-directed, to join in special activities and events sponsored by the fitness center, and to plan for the final 18 months of less intensive supervision.
During the 6-month intensive intervention, participants randomized to the lifestyle group were divided further into small groups of no more than 13 participants. These groups met for 1 h one night each week for the first 16 wk of the intervention and then 1 night once every other week through week 24. Facilitators experienced in conducting behavior change groups and supervised by a Ph.D. clinical health psychologist helped participants use problem-solving approaches to learn cognitive and behavioral skills appropriate for their level of motivational readiness for physical activity adoption and life circumstances. Participants were told their goal should be to accumulate at least 30 min of at least moderate intensity activity on most days of the week in any way that could be adapted to their particular lifestyle. They also were told they would be allowed to progress at their own rate. We assessed stage of motivational readiness (28) each month and gave each participant a motivational stage manual tailored for his or her level of readiness (27). Participants received curriculum materials for each weekly session. These materials were based on the behavioral and cognitive strategies fundamental to the stages of motivational readiness (26-29), decisional balance (28), and self-efficacy (30). As participants progressed through the Lifestyle curriculum, they gradually problem-solved how to fit physical activities of at least a moderate intensity into their individual lifestyles. Because the physical activity types and amounts were unique to each person's lifestyle and stage of motivational readiness, it is not possible to specify the exact physical activity dose of the lifestyle group as a whole.
Statistical analyses. ANCOVA was used to compare the lifestyle and structured groups' changes in physical activity and cardiorespiratory fitness after 6 months of intervention. Change scores for the outcome measures were adjusted for the baseline value of the outcome measure, age, BMI (kg·m2), gender, cohort (three groups), and ethnicity (nonhispanic Caucasian, African American, or Mexican-American). Analyses were limited to persons with complete major outcome data at a 6-month follow-up. Unless otherwise noted, all results reported are the least-squares adjusted means for changes in the outcome measure by the intervention group. A logistic regression analysis, adjusting for baseline pace of walking, age, BMI, gender, cohort, and ethnicity, was conducted on the categorical data on pace of walking.
Multivariate ANOVA (MANOVA) was used to assess changes in moderate, hard, and very hard activities, gender differences, and interactions of treatment group with gender. All covariates listed above were also included in these analyses. Statistical analyses were performed using SAS Version 6.11 software (40), and all reported P values are two sided.
Baseline measures and measurement compliance. Data for baseline measures of selected characteristics of participants in Project Active by treatment group are provided in Table 1. More detailed information on baseline characteristics is published elsewhere (24). There was no difference between intervention groups in those who returned for follow-up testing. Ninety-one percent. of both lifestyle and structured participants completed the PAR, and 82% of lifestyle and 84% of structured participants completed the maximal treadmill test. Reasons for not completing the treadmill test included illness, injury, and dislike of the treadmill test.
Physical activity. Adjusted mean changes, 95% confidence intervals, and probability values for between group differences are presented in Table 2. Both lifestyle and structured groups significantly increased energy expenditure over baseline (P = 0.0001). The lifestyle group increased their physical activity by 4.6%, and the structured group increased their physical activity by 4.0%; however, there was no significant difference between groups for change in energy expenditure. The PAR allows assessment of time spent in moderate, hard, and very hard activities over the course of the previous week. There were differences between the two groups for moderate activities with the lifestyle group increasing participation in moderate intensity activities nearly twice as much as the structured group (P = 0.02). On the other hand, the structured group expended nearly two times greater amounts of energy in hard activities, although this was not statistically significant (P = 0.18). The increase in very hard activities was equivalent between the two groups (P = 0.96).
In addition to the PAR, we obtained data on hours spent sitting, amount of walking, pace of walking, and stair climbing. Similar to the PAR, significant decreases from baseline were found for both groups on variables of time spent sitting and significant increases in walking and stair climbing. The percentage decrease for hours sitting was 9.3% for the lifestyle group and 12.1% for the structured group. For stairs climbed and minutes walked, the percentage increase for the lifestyle group was 64.0 and 25.0%, and for the structured group the percentage increase was 30.2 and 20.9%. There was a significant increase in the pace of walking from baseline (P < 0.001), and the lifestyle group increased their pace of walking more than the structured group (P = 0.009).
The goal for the first 6 months of the study was to increase physical activity 3 kcal·kg−1·d−1. Figure 1 shows the individual changes from baseline in total energy expenditure for both the lifestyle and structured groups. The goal of 3 kcal·kg−1·d−1 was achieved by 21% of lifestyle and 14% of structured participants.
Cardiorespiratory fitness. ANCOVA revealed a significant increase in treadmill time (P < 0.001), V˙O2peak (P < 0.001), and decrease in submaximal heart rate at the end of stage 2 of the treadmill test (P < 0.001) for both lifestyle and structured groups (Table 2). There also were significant between group differences for these variables (P < 0.001). The percentage increase in treadmill time for the lifestyle group was 6% compared with the structured group whose percentage increase was 11%.
A goal of a 5 mL·kg−1·min−1 increase in V˙O2peak was set for the first 6 months. This is a 17 and 22% improvement over baseline for men and women, respectively. There were 18% of lifestyle participants and 31% of structured participants who met the 5 mL·kg−1·min−1 goal (Fig. 2).
Adherence to the interventions. Because of intervention requirements for participation, adherence to the interventions was calculated differently for the two groups. We computed adherence to the structured intervention based on a criterion of attending at least three exercise sessions per week during this 6-month period. The criterion for adherence to the lifestyle intervention was attending group meetings, not exercise participation. For the lifestyle group, 78% attended two-thirds or more of all group meetings, and for the structured group, 80% logged at least three or more sessions per week for the 6-month period. Attending at least two-thirds of intervention sessions has been considered to be an adequate dose of intervention in other physical activity studies (23,41). We compared the effects of greater adherence on the primary outcomes by performing an ANOVA combining both treatment groups and found intervention adherence to be a significant predictor of change in total energy expenditure (P = 0.007) and cardiorespiratory fitness (P < 0.001).
Treatment differences between men and women. The study was not powered to detect treatment differences by gender; however, whether there were differences between men and women in effectiveness of the interventions for each of the treatment groups is of interest. MANOVA, adjusting for baseline measures, age, BMI, cohort, and ethnicity, was conducted on the major outcome variables of physical activity and cardiorespiratory fitness. These analyses showed significant differences by gender for total activity (P < 0.001), moderate activity (P < 0.001), hard activity (P = 0.02), very hard activity (P = 0.01), and V˙O2peak (P < 0.001) with men having greater values than women. For men in the lifestyle group, there was over a twofold difference in moderate intensity activities compared with structured men or with women in either treatment group. For hard activity, structured men increased these activities almost three times more than men in the lifestyle group, whereas women in the lifestyle and structured groups increased their hard activities by nearly the same amount. For very hard activities, men increased these activities much more than women regardless of intervention group. Men in the structured group had significantly higher V˙O2peak than men in the lifestyle group or women in either intervention group.
The major finding in this report is that after 6 months of intensive intervention the lifestyle physical activity intervention was as effective in increasing physical activity as the structured exercise intervention. Also, those in the lifestyle group significantly increased their cardiorespiratory fitness from baseline as did the structured group, although those in the structured exercise group increased their fitness significantly more. A major difference of the lifestyle intervention from structured exercise is the emphasis on behavioral skill building rather than exercise prescription of bouts of exercise, and urging the integration of a wide variety of moderate intensity activities accumulated over the course of the day such as that recommended by the CDC and ACSM (36) (i.e., each person should accumulate 30 min of moderate intensity physical activity on most, preferably all, days of the week). The Lifestyle approach described in this report is a novel alternative in promoting physical activity. Also, these results are consistent with our analyses of cardiovascular disease risk profiles, which demonstrate the similarity of findings between lifestyle and structured groups in improvements in their total cholesterol/HDL-C ratio, systolic and diastolic blood pressures, and percent body fat (12).
Other investigators have examined determinants (39) and barriers to physical activity and sought to eliminate barriers while incorporating behavior change principles (4,21,25,32,33,43). For example, Epstein and colleagues (15) found comparable fitness improvements and weight loss in children who were randomly assigned to a lifestyle group based on behavior change principles compared with an aerobic training group. In adults, King et al. (22) recently completed a 2-yr intervention that employed behavior change principles based on social cognitive theory (2) in an intervention that varied intensity (3 d·wk−1 [vigorous] or 5 d·wk−1 [moderate]) format (group or home-based). All groups had significant increases of 5 to 10% in cardiorespiratory fitness from baseline, and these were maintained or increased during the second year. Intermittent bouts of exercise also have been proposed to address barriers of lack of time and other objections to gym-based programs (6). Intermittent exercise has been demonstrated to increase fitness (9,13), and more recently it has been shown to enhance adherence, increase energy expenditure, and increase fitness by about 5% in a 20-wk study of obese women undergoing a dietary/physical activity intervention (20). Our results are comparable in terms of percentage increase in fitness and estimated energy expenditure and underscore the importance of incorporating behavior change principles in physical activity interventions.
The increase in cardiorespiratory fitness was significantly greater in the structured group than in the lifestyle group. This was not surprising because these participants began their program of becoming physically active during the first week of entering the study. These participants were required to come to our fitness center three times per week for three supervised sessions of at least 20 min in duration during the first week and progress to coming at least five. times per week. Participants who did not attend any sessions during a 1-wk period were telephoned for a problem-solving session to encourage them to return as quickly as possible. On the other hand, individuals in the lifestyle group began their program by examining their activities during the week and the amount of time they spent sitting. As a group, they used problem-solving techniques to decrease their time sitting and to find time in their day to incorporate short bouts of moderate intensity activities. In addition, the lifestyle group also practiced behavior change strategies and discussed how people change their behavior (i.e., changing is a process of trial and error, and each person changes at his or her own rate). The lifestyle intervention was less regimented with each person solving problems with the help of the group. Participants also were allowed to increase their activity according to their motivational readiness to change. They took longer to become active, thus, it is reasonable to think that the amount of change in fitness would not be as great as in the structured group, although both groups were achieving comparable amounts of activity at the end of 6 months.
Another important difference between the lifestyle and structured groups that may have differentially affected fitness change is the intensity of activities of the two groups. For example, the lifestyle group increased their moderate intensity activities almost twice as much as the structured group. Increasing moderate activities was a specific focus of the lifestyle intervention; therefore, it is not surprising that there was a significant between-group difference. However, for hard intensity activities, differences between groups were reversed with the structured group having nearly a twofold difference in hard activities compared with the lifestyle group. Again, more vigorous activities were a focus of the structured intervention, so this finding is not surprising as others have found greater increases in cardiorespiratory fitness in groups who exercise at a higher intensity (11).
The physical activity and physical fitness goals of 3 kcal·kg−1·d−1 or 5 mL·kg−1·min−1 used in this study were established before the CDC/ACSM recommendations (36), the NIH Consensus statement (35), and the Surgeon General's Report on Physical Activity and Health (42) and may have been overly ambitious for a sedentary population. A review of Figures 1 and 2 shows that about one-fifth of participants reached the physical activity goal established for our study, and almost one-fifth of lifestyle and one-third of structured participants reached the fitness goal. More recent public health recommendations about increasing physical activity advises a goal of approximately 2 kcal·kg−1·d−1. Applying this less stringent criterion to our data showed that 32% of lifestyle and 28% of structured participants met this criterion (35,36,42). In a previous paper, we operationally defined meeting the CDC/ACSM criterion with a brief self-administered questionnaire (12). This questionnaire has demonstrated reliability and validity with the PAR (31). Altogether, these results give reason for optimism about the efficacy of lifestyle approaches for increasing physical activity, cardiorespiratory fitness, and health-related outcomes. This is particularly true when one examines the increasingly positive effects of adherence on the outcomes; on the whole, adherence in both groups was high.
Although this study was not powered to examine intervention effects on men and women separately, possible gender-treatment effects were explored. For total energy expenditure, both interventions had greater effects among men when compared with women. An examination of the components of total energy expenditure illustrates notable gender treatment differences. For example, the change in moderate intensity activities is almost two times greater in the lifestyle men when compared with men in the structured group. For hard physical activity, this was reversed. The same finding was not true for women; lifestyle women did 35% more moderate intensity activity and the same amounts of hard activity as women in the structured group. In terms of increasing cardiorespiratory fitness, the men increased their fitness more than the women in either treatment group, and structured men and women increased their cardiorespiratory fitness more than lifestyle men and women.
There are limitations of this study. This includes lack of a "no contact" control and the select group of volunteers from the community with a high educational level (e.g., 16 yr of formal education was the average). We believe a "no contact" control group was not necessary. There is well-documented evidence of poor long-term adherence to exercise in groups that are left to exercise on their own. Because of this poor adherence and existing scientific evidence on the health benefits of regular physical activity, it did not seem desirable, necessary, or ethical to have a "no contact" control group. The approach we adopted in this study is analogous to other National Heart, Lung, and Blood trials where a novel intervention (i.e., lifestyle) is compared with a traditional or usual intervention (i.e., structured).
The other limitation relates to the highly educated volunteers from the community. One could argue that these study participants may have been more motivated than others who did not volunteer; however, they are likely to be similar to others who begin a program to increase their activity. We did examine the effect of education in the two treatment groups and found that the only significant difference between those with a college education and those without a college education was that those with a college education had significantly higher adherence (P = 0.04) to the structured intervention than those without. In the structured group, there were no other significant differences in physical activity, cardiorespiratory fitness, or health-related outcomes by educational attainment. In the lifestyle group, attendance and all other outcomes were nearly the same in the two education groups. In this efficacy study, the two treatments had similar overall effects, and the extent to which these findings can be generalized is not known.
Despite these limitations, the results presented here demonstrate that a lifestyle intervention which incorporates established behavior change principles and a flexible approach to promotion of activity is effective for increasing physical activity and fitness in sedentary adults over the short-term. These findings demonstrate that a lifestyle approach is a viable option to traditional exercise programming and home-based structured programs in public health efforts to increase population physical activity levels. Although both structured and lifestyle interventions are effective, certain individuals may do best with one approach instead of the other. It is important to test these interventions in other populations and to evaluate whether it is possible to match treatments to individuals to enhance success. These results will aid public health efforts to provide multiple alternatives to increase physical activity in sedentary individuals.
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