Preventive Medicine 33, 441–452 (2001)doi:10.1006/pmed.2001.0914, available online at http://www.idealibrary.com on

Exercise and the Transtheoretical Model:A Longitudinal Test of a Population Sample1

Ronald C. Plotnikoff, Ph.D.,*,2 Stephen B. Hotz, Ph.D. (C.Psych.),† Nicholas J. Birkett, M.D., M.Sc.,†and Kerry S. Courneya, Ph.D.‡

*Centre for Health Promotion Studies, Alberta Centre for Active Living, and Faculty of Physical Education, University of Alberta,Edmonton, Alberta, Canada T6G 2T4; †Department of Epidemiology and Community Medicine, University of Ottawa,

451 Smyth Road, Ottawa, Ontario, Canada K1H 8M5; an,

e

titioners, and program planners are provided. q 2001

Edmonton, Alberta

Published online S

Background. The purpose of this study was to test theability of the Transtheoretical Model (TTM) to predictexercise stage transition of individuals in a large,untreated-population-based, random sample of Cana-dian adults (18–65 years of age) over two consecutivetime periods.

Methods. Assessments of TTM’s stage of exercisebehavior change, self-efficacy, pros, cons, experientialprocesses, and behavioral processes were made atbaseline (time 1), 6 months (time 2), and 1 year (time 3).Six hundred eighty-three men and women, identifiedthrough random-digit telephone dialing, completed allmeasures across the three time points. Within eachtime period (time 1–2; time 2–3) participants were cate-gorized as having regressed (moved back at least onstage), remained (no stage change), or progressed(moved forward at least one stage). Baseline TTM con-structs were analyzed for their ability to predict

change transition across the two time periods.

Results. Of 40 possible predictions (20 for each timeperiod) 18 (45%) were supported.

Conclusions. Overall, the findings demonstrate par-tial support for the internal validation of TTM in the

1 This study was funded by a grant (NA3162) from the Heart andStroke Foundations of Canada (Ontario) to Ronald C. Plotnikoff, whois supported by a Population Health Investigator Award from theAlberta Heritage Foundation for Medical Research. Kerry S. Cour-neya is supported by an Investigator Award from the Canadian Insti-tutes of Health Research and a Research Team Grant from the Na-tional Cancer Institute of Canada (NCIC) with funds from theCanadian Cancer Society (CCS) and the CCS/NCIC SociobehavioralCancer Research Network.

2 To whom reprint requests should be addressed at the Centre forHealth Promotion Studies, University of Alberta, 5-10A UniversityExtension Centre, 8303–112 Street, Edmonton, Alberta, Canada T6G2T4. Fax: (780) 492-9579.

44

d ‡Faculty of Physical Education, University of Alberta,Canada T6G 2H9

ptember 12, 2001

exercise domain. Implications of the findings are dis-cussed and future directions for researchers, prac-

American Health Foundation and Academic Press

Key Words: Transtheoretical Model; stages of change;physical activity; exercise behavior; behavior change.

INTRODUCTION

Cardiovascular disease is the greatest cause of mor-tality throughout the developed world [1]. Based onstrong epidemiological evidence, the World Health Or-ganization has classified physical inactivity as one ofthe primary risk factors of coronary artery disease(CAD) [2]. Although a meta-analysis of 27 cohort stud-ies concluded that regular physical activity produced abeneficial effect in terms of a 35 to 55% decrease inmyocardial infarction [3], physical inactivity from apopulation-attributable risk perspective poses greaterCAD risk than the other primary risk factors of ciga-rette smoking, hypertension, and hypercholesterolemia[4,5]. Physical inactivity is also a contributing factor forType II diabetes, colon cancer, back pain, hypertension,obesity, osteoporosis, anxiety, depression, and stress [6].The discovery of effective means of interventions to im-prove exercise adherence has become a major focuswithin preventive medicine, public health, and healthpsychology domains [7–9]. The Transtheoretical Model(TTM) or “Stages of Change” developed by Prochaska

and DiClemente [10] has achieved widespread atten-tion from researchers and practitioners involved in be-havior change interventions for a variety of health-re-lated behaviors, including exercise [11,12].

TTM draws key variables from some of the major

1 0091-7435/01 $35.00Copyright q 2001 by American Health Foundation and Academic Press

All rights of reproduction in any form reserved.

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442 PLOTNIKO

social–cognitive models and integrates them on the ba-sis of testable assumptions. The strengths of TTM re-garding exercise behavior are its sensitivity to degreeof readiness and incremental change over time and itsspecification of change-relevant, profile differences be-tween stages. The TTM acknowledges that people differin their readiness to adopt new behaviors and thatreadiness to change can be understood in terms of fourkey constructs: (1) stage of change, (2) self-efficacy, (3)decisional balance (pros and cons), and (4) processes ofchange (experiential and behavioral).

Individuals adopting a new behavior move througha series of stages of change. The model suggests thatpeople progress through five stages: (1) Precontempla-tion (no intention to change behavior in next 6 months),(2) Contemplation (intention to change within 6months), (3) Preparation (small or inconsistentchanges), (4) Action (active involvement in behavior forless than 6 months), and (5) Maintenance (sustainedbehavior change for at least 6 months). The movementthrough these stages does not always occur in a linearfashion as individuals may make several attempts (i.e.,relapse phases) before reaching Maintenance. By dis-tinguishing people vis-a-vis readiness to change, themodel identifies the particular requirements of eachstage and thus the nature of interventions that will berelevant at different points in the change process.

Self-efficacy relates to confidence in one’s ability toengage in a specific behavior and resist temptation torelapse [12,13]. While less salient in the earlier stages,self-efficacy increases as one progresses from Precon-templation to Maintenance and remains high as thebehavior is sustained [14].

Decisional balance involves the perceived “pros” (ad-vantages) and “cons” (disadvantages) of continuing thecurrent behavior or adopting the new behavior [12,13].Decisional balance also varies across stage of change.In Precontemplation, the pros are low (i.e., not salient),with cons outweighing pros. By Contemplation or Prep-aration the salience of the pros increases to the samelevel as the cons, with pros eventually outweighing consin the Action and Maintenance Stages [12,15].

Processes of change, the most understudied tenantof the model, are the strategies and techniques peopleuse to change a problem behavior or adopt a healthybehavior. The processes of change consist of five experi-ential processes (i.e., consciousness-raising, dramaticrelief, environmental reevaluation, social liberation,and self-reevaluation) and five behavioral processes(i.e., counterconditioning, helping relationships, rein-forcement management, stimulus control, and self-lib-

eration) [12,13]. People at different stages of changeare hypothesized to use distinct processes of change.The use of experiential processes is emphasized in thepreaction stages while the use of behavioral processesis greatest in the Action and Maintenance stages

F ET AL.

[12,13]. In the exercise domain, Marcus and colleagueshypothesize that stage progressors increase their use ofthe processes, whereas relapsers would decrease theirprocess use; those who maintain sedentary behaviorwould not increase their process use, nor would thosemaintaining their active habits; however, this lattergroup would use the process more than the formergroup [16].

Emerging study findings have examined TTM in theexercise domain across a number of age groups, work-site settings, places of residence, and countries. Thesestudies provide some support in explaining the adoptionof physical activity [see 14,17–19 for partial reviews].However, as in other health domains, the research onTTM has primarily focused on cross-sectional studies,which offer the weakest evidence for theoretical testingof a stage model [20]. Even though intervention designsare beginning to emerge [8,18,21–24], these studieshave not tested all of TTM’s hypothesized mediatingconstructs thought to induce stage transitions [25].Longitudinal designs with repeated assessments ofthese constructs are needed to examine this issue [16,25–27]. To date there appears to be limited publishedTTM data across any health behavior that has exam-ined all of the TTM’s mediating constructs over multipletime periods. Marcus and colleagues’ worksite studiesexamined the processes of change to predict exercisestage transition at 6 months [16] and self-efficacy, pros,cons, and stage to predict physical activity behavior in a6-month follow-up [28]. A randomized trial on physicalactivity that assessed the TTM constructs on 235 seden-tary adults reported that those who increased theiruse of the behavioral and experiential strategies, self-efficacy, and the benefits to barriers index for physicalactivity were significantly more likely to achieve recom-mended activity levels [29]. In the smoking domain,Herzog and colleagues recently assessed the pros, thecons, and 6 of the 10 processes to predict stage transi-tion at two subsequent time periods [26].

There has been a call to test the model with samplesmore representative of the population [16], as the TTMliterature is silent in terms of examining the generaliz-ability of the model in large community- and popula-tion-based samples. Further, there appears to be nopublished longitudinal study to date that has testedthe TTM’s internal validity (all constructs) to predictstage transitions. A longitudinal design including allTTM’s cognitive components to determine the causationof stage transitions would be, to date, the strongest testof TTM’s internal validity. The purpose of the presentstudy was therefore to examine TTM’s constructs (i.e.,

self-efficacy, pros, cons, and processes of change) to pre-dict exercise stage movement of individuals in a large,untreated-population-based sample of adults over twoconsecutive time periods. Based on the TTM literature[10,12,13,30,31] and specific TTM studies in its exercise

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EXERCISE AND THE TRA

domain [14,16,32–34] it was hypothesized that forwardmovement across the stages would be predicted byhigher scores on self-efficacy, pros, experiential proc-esses, and behavioral processes and lower scores oncons.

METHODS

Participants and Procedures

Participants were a representative sample of 1,602adults between the ages of 18 and 65 years from theOttawa-Carleton region of Ontario, Canada. A com-puter-assisted telephone interviewer system was used,which randomly generated resident telephone numbersfrom the region’s telephone exchange. One adult fromeach household was randomly selected based on thenearest birthday. The telephone survey (approved byan ethical review board) was administered by trainedprofessional interviewers and conducted during March1997. The telephone randomization protocol produced4,122 eligible households (i.e., at home, appropriate age,English-speaking). Of the 4,122 eligible households,there were 1,876 refusals by the household memberanswering the telephone and a further 644 refusals bythe selected household adult, resulting in 1,602 time 1respondents of eligible households. The 1,602 individu-als were contacted to be surveyed again by the tele-phone protocol at 6 months during September 1997(time 2) and through a mail-out survey at 12 monthsduring March 1998 (time 3). The attrition at times 2and 3 resulted in 683 individuals (43.9% of the originalsample) completing all three survey periods.

The demographic profile of the sample (N 5 683) wasas follows: 54.0% were female, mean age was 40.6 years(SD 5 11.04), 63.4% were married/common law, 44.1%had completed university, 34.0% had children underage 13 at home, 21.4% were current smokers, 32.4%drank alcohol more than once per week, and the meanbody mass index was 25.21 (SD 5 5.91). The scalemeans for a health and physical limitations (i.e., healthcondition, injury, or disability) measure were all below1 (on a 6-point measure ranging from “no limitation”(0) to “completely limited” (5)) across the three timeperiods. These participants (N 5 683) were comparedwith the 874 who completed only the time 1 assessment,which revealed similar demographic, cognitive, and be-havior (i.e., stage of change for physical activity, energyexpenditure) scores.

Instruments

The ordering of the TTM measures were the samefor all participants. Each telephone interview includedassessments of stage of change, followed by self-efficacy,pros, cons, experiential processes of change, behavioralprocesses of change, and background information. All

STHEORETICAL MODEL 443

questions were related to regular vigorous physical ac-tivity, which was defined for participants as “strenuousactivities which usually make you sweat, breatheharder, and feel your heart beat.” Examples of vigorousphysical activities were provided. The term “regular”was defined as “at least three times per week for atleast 20 min each time.” Participants were instructed toanswer all questions based on this definition of regularvigorous physical activity.

Stage of change was assessed using an algorithmwith responses in a yes/no format. This measurementstrategy has been suggested as the most reliable andvalid in the exercise domain [35]. Stage was coded from1 (Precontemplation) through 5 (Maintenance). ThePearson correlation (r) of the sample’s stage measurewith energy expenditure was 0.40 (P , 0.001).

Development of TTM’s Constructs

Slightly modified TTM measures of self-efficacy, pros,cons, and the behavioral and experiential processes ofchange, based on existing TTM measures of exercise,were developed for the Canadian population. Inter-views were conducted with a cross section of the commu-nity to confirm, add, and reword Marcus and colleagues’existing measures [32,36,37] of these constructs for self-efficacy [36], pros and cons [32], and processes of change[37]. From these responses, a telephone interview ques-tionnaire was developed and pretested with profes-sional and nonprofessional groups to establish itemcomprehension. One hundred thirty-five respondentswere involved in the development and prepilot phasesof instrument development. The instrument was subse-quently pilot tested (via randomized digit dialing) with500 adults between the ages of 18 and 65 to establishconstruct validity and internal consistency (Cronbach’sa) of the measures. Principal component analyses es-tablished unidimensionality (1) between the behavioraland the experiential processes and (2) between the prosand the cons. Cronbach a’s were greater than 0.70 onall of the TTM constructs (i.e., self-efficacy, pros, cons,experiential processes, and behavioral processes). A 2-week test–retest was completed with 30 individuals toestablish the reproducibility of the TTM constructs withtest–retest reliability coefficients of 0.60 to 0.91 for thefive TTM measures (the 10 processes of change meas-ures ranged from 0.63 to 0.90). All pretesting was con-ducted in the catchment area within 2 months of themain study.

Measures

Self-efficacy (8 items) [36] was assessed with 5-pointrating scales, ranging from 1 (not at all confident) to 5(extremely confident), assessing perceived confidence ofdoing regular vigorous physical activity under variouscircumstances, e.g., when tired. Pros and cons [32,38]

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were assessed by 5 items, each measured on 5-pointscales ranging from 1 (not at all) to 5 (very much).Respondents indicated the extent to which they agreedor disagreed with statements about regular vigorousphysical activity (e.g., would reduce tension or managestress (pro); would take too much of my time (con)).

Processes of change were assessed by a modificationof the Processes of Change Questionnaire (PCQ) devel-oped and validated specifically for the exercise domainby Marcus and coresearchers [37]. The PCQ contains39 items that measure the 10 processes of change [37].Our instrument contained a slightly modified, shortversion of 21 items. Individuals were asked to recallthe past month and to rate the frequency of occurrenceof each item on 5-point scales ranging from 1 (never)to 5 (very often). The behavioral processes measureconsisted of 11 items: 2 items each for countercondition-ing, contingency management, self-liberation, andstimulus control, while helping relationships comprised3 items. The experiential processes measure contained10 items: 2 items each for consciousness-raising, dra-matic relief, environmental reevaluation, self-reevalua-tion, and social liberation.3

The psychometric properties for the time 1 sample(n 5 1,602) included confirmation of the unidimension-ality of the pros and cons and of the aggregated experi-ential and behavioral processes through two separatefactor analyses using LISREL. Adjusted goodness-of-fit indices were 0.90 and 0.89, respectively, for the pros–cons and the processes models. Internal consistencies(a) for self-efficacy, pros, cons, experiential processes,and behavioral process for the 1,602 sample rangedfrom 0.66 to 0.86 and were 0.90, 0.82, 0.72, 0.81, and0.89, respectively, for the final sample of 683. Furtherpsychometric details on the pros and cons scales arereported elsewhere [38].

Main Data Analysis

The sample size and distribution of responses werenot sufficient to examine all possible patterns of stagechange over three time points (i.e., 5 3 5 3 5 5 125)or even two time points (i.e., 5 3 5 5 25). Three stepswere taken to address this issue. First, the two transi-tion periods (time 1–2 and time 2–3) were analyzedseparately, therefore allowing examination of stagetransitions over the two consecutive 6-month periods.Time 1 stage was the baseline stage for the first transi-tion period (time 1–2) and time 2 stage was the baseline

stage for the second transition period (time 2–3). Sec-ond, the Action and Maintenance stages were combineddue to the small numbers of participants in the Actionstage, which resulted in four baseline stages: Precon-templation, Contemplation, Preparation, and Action/

3 The entire TTM instrument can be obtained from the first author.

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Maintenance. Third, the four possible transitions foreach baseline stage were collapsed into general pat-terns of change labeled regressed (moved backward atleast one stage), remained (no stage change), or pro-gressed (moved forward at least one stage). Conse-quently, the possible stage transitions for baseline Pre-contemplation were remained or progressed; thepossible stage transitions for baseline Contemplationand Preparation were regressed, remained, or pro-gressed; and the possible stage transitions for baselineAction/Maintenance were regressed or remained.

To test the model, the time 1 TTM constructs wereused to predict the time 1–2 stage transitions and thetime 2 TTM constructs were used to predict the time2–3 stage transitions. These analyses were performedwithin each of the four baseline stages to test 40 hypoth-eses, 20 for each time period. Baseline stages with onlytwo possible transitions (i.e., Precontemplation andAction/Maintenance) were analyzed using independentt tests. Baseline stages with three possible stage transi-tions (i.e., Contemplation and Preparation) were ana-lyzed using univariate F tests with planned contrastscoded 21, 0, and 11 for those who regressed, remained,and progressed, respectively (contrast weights were re-versed for the cons of exercise). The t and P values forthe planned contrasts are reported. The more powerfultechnique of employing planned contrasts over post hoccomparisons for hypotheses testing [39] is also justifiedby Herzog and colleagues in their prospective test ofTTM in the smoking domain [26]. P levels were notadjusted for the main analyses because the sample sizes

for some of the categories were small, which would haveimplications on power [40]. However, exact P levels forall main analyses (and effect sizes for the F tests) arereported so readers can assess the magnitude of theresults for themselves.

RESULTS

Descriptive statistics and zero-order correlationsamong each of the TTM constructs at times 1 and 2are presented in Table 1. Table 2 provides the stagetransition patterns from time 1–2 and time 2–3.

The results concerning the prediction of stage transi-tions are presented for both time periods (i.e., time 1–2and time 2–3) for the baseline stages of Precontempla-tion (Table 3), Contemplation (Table 4), Preparation(Table 5), and Action/Maintenance (Table 6). The expe-riential and behavioral processes results are reportedas aggregated scores of their respective measures.

Transition from Precontemplation

None of the TTM constructs predicted stage transi-tion out of Precontemplation at time 1–2. Self-efficacy(P , 0.005), pros (P 5 0.005), and behavioral processes

8. Cons 20.03 20.20 1.92 0.72

dt

9. Experiential processes10. Behavioral processes

Note. Correlations . 0.07 are significant at the 0.05 level (two-taileprocesses; BP, behavioral processes; SE, self-efficacy; T1, time 1; T2,

(P , 0.05) significantly predicted forward stage pro-gression from this stage at time 2–3.

Transition from Contemplation

Self-efficacy (P , 0.001), pros (P , 0.05), and behav-ioral processes (P , 0.005) significantly predicted for-ward transition at time 1–2. Self-efficacy (P 5 0.05),pros (P 5 0.001), and behavioral processes (P , 0.05)also predicted forward movement at time 2–3.

Transition from Preparation

Preparation 7 29Action 0 20Maintenance 8 49Total 71 207

Note. PC, Precontemplation; CO, Contemplation; PR, Preparation; A

0.61 2.51 0.772.61 0.84

). M, mean; SD, standard deviation; P, pros; C, cons; EP, experientialime 2.

Retention in Action/Maintenance

Self-efficacy (P , 0.005) and behavioral processes(P , .05) predicted retention in the Action/Maintenancestage at time 1–2. Self-efficacy (P , 0.001), pros (P ,0.005), cons (P , 0.001), experiential processes (P ,0.05), and behavioral processes (P 5 0.001) predictedretention for this stage at time 2–3.

Individual Processes of Change

EXERCISE AND THE TRANSTHEORETICAL MODEL 445

TABLE 1

Descriptive Statistics and Zero-Order Correlations among TTM Constructs at Time 1 and Time 2

2 3 4 5 6 7 8 9 10P-T1 C-T1 EP-T1 BP-T1 SE-T2 P-T2 C-T2 EP-T2 BP-T2 M SD

Time 11. Self-efficacy 0.21 20.30 0.06 0.30 0.69 0.25 20.26 0.09 0.32 3.11 0.842. Pros 20.10 0.40 0.43 0.20 0.57 20.10 0.35 0.31 3.99 0.873. Cons 20.02 20.23 20.26 20.08 0.48 20.02 20.20 1.92 0.754. Experiential processes 0.60 0.05 0.37 20.05 0.58 0.41 2.48 0.775. Behavioral processes 0.29 0.39 20.20 0.42 0.55 2.57 0.84

Time 26. Self-efficacy 0.33 20.27 0.13 0.37 3.15 0.837. Pros 20.07 0.50 0.47 3.96 0.92

The separate analyses for each of the 10 processes

of change constructs (5 experiential and 5 behavioral)None of the TTM constructs predicted stage move-

ment out of Preparation at time 1–2. Self-efficacy (P , across each of the stages generally reflected the findingsof their higher order constructs. The significant experi-0.001) and cons (P , 0.05) predicted forward transition

out of Preparation at time 2–3. ential processes for Action/Maintenance retention were

TABLE 2

Stage Transitions over Two Consecutive 6-Month Time Periods (N 5 683)

6 months

Baseline PC CO PR AX MN Total

Time 1 to time 2Precontemplation 41 18 6 3 10 78 (11.4%)Contemplation 29 74 28 23 45 199 (29.1%)Preparation 7 20 23 14 33 97 (14.2%)Action 9 16 7 10 15 57 (8.3%)Maintenance 8 24 19 21 180 252 (36.9%)Total 94 152 83 71 283 683 (100%)

Time 2 to time 3Precontemplation 40 38 7 2 7 94 (13.8%)Contemplation 16 71 20 24 21 152 (22.3%)

21 8 18 83 (12.2%)9 8 34 71 (10.4%)

27 22 177 283 (41.4%)84 64 257 683 (100%)

X, Action; MN, Maintenance.

Pros 3.06 (1.21) 3.67 (1.02) 2.63 0.005Cons 2.16 (0.90) 2.24 (0.72) 0.48 0.318Experiential processes 2.17 (0.94) 2.33 (0.76) 0.94 0.174

Behavioral processes 1.84 (0.90) 2.19 (0.83) 1.99 0.025

Note. P level is one-tailed.

environmental reevaluation (P , 0.005, time 1–2), con-sciousness-raising (P 5 0.01, time 1–2), environmentalreevaluation (P , 0.05, time 2–3), and self-reevaluation(P , 0.005, time 2–3). Social liberation (P , 0.05, time1–2), consciousness-raising (P , 0.05, time 2–3), andsocial liberation (P , 0.05, time 2–3) were predictorsfor forward transition from Contemplation. Significantbehavioral processes results were reported for thoseprogressing from Precontemplation, i.e., countercondi-tioning (P 5 0.01, time 1–2) and self-liberation (P ,0.05, time 1–2); advancing from Contemplation, i.e.,counterconditioning (P , 0.05, time 1–2), helping rela-tionships (P , 0.05, time 1–2), stimulus control (P ,0.01, time 1–2; P , 0.05, time 2–3), reinforcement man-agement (P , 0.05, time 2–3), and self-liberation (P ,0.01, time 2–3); and retaining in Action/Maintenance,i.e., counterconditioning (P , 0.05, time 1–2, time 2–3),reinforcement management (P , 0.01, time 1–2, time2–3), stimulus control (P , 0.05, time 1–2; P , 0.001,time 2–3), and self-liberation (P , 0.005, time 2–3).Given that there were 80 tests (i.e., t tests and F-planned contrasts) conducted for the individual proc-esses of change measures, the P level in the above re-sults should be considered significant at the 0.01level [39].

All analyses in Tables 3–6 (and each of the five experi-ential and five behavioral processes) were also con-ducted with age and sex as covariates. All statistically

significant findings remained unchanged (P , 0.05), asdid nonsignificant findings.

Table 7 summarizes the results of the TTM testedhypotheses to predict forward stage transition (or re-taining stage for Action/Maintenance) over the two time

446 PLOTNIKO

TABLE 3

Comparison of TTM Constructs for Persons in thePrecontemplation Stage at Times 1 and 2 Who Remained

or Progressed from That Stage over a 6-Month Period

Stage change over6 months

PTTM Remained Progressed t level

Time 1–time 2 (n 5 78) (n 5 41) (n 5 37)Self-efficacy 2.11 (0.89) 2.19 (0.88) 0.41 0.341Pros 3.62 (1.08) 3.73 (1.08) 0.45 0.329Cons 2.21 (0.92) 2.36 (0.86) 0.74 0.233Experiential processes 2.23 (0.88) 2.36 (0.88) 0.68 0.249Behavioral processes 2.01 (0.87) 2.29 (0.97) 1.29 0.100

Time 2–time 3 (n 5 94) (n 5 40) (n 5 54)Self-efficacy 1.91 (0.91) 2.46 (0.80) 3.08 0.002

FF ET AL.

periods. Of 40 possible predictions (20 for each timeperiod) 18 (45%) were supported.

DISCUSSION

This study set out to test the TTM components topredict exercise stage transitions over two consecutive6-month periods in a randomly selected adult popula-tion-based sample. This is the first TTM study to testthe entire model (i.e., stage, self-efficacy, pros, cons,and 10 process of change constructs) in a longitudinal,untreated-population design. The findings provide par-tial support toward the internal validation of TTMfor exercise.

As the model postulates, self-efficacy should progresswith increasing stages. The monotonic increase in self-efficacy with stage advancement has been consistentlyobserved in cross-sectional studies that show good dis-crimination between stages, with individuals in higherstages exhibiting higher self-efficacy than those inlower stages [33,34,36,41]. Our longitudinal results pro-vide moderate to strong support of self-efficacy as apredictor of forward stage transition. The study re-vealed that self-efficacy scores were significantly higherfor those progressing out of Precontemplation (time 2–3), Contemplation (time 1–2, time 2–3), and Prepara-tion (time 2–3) and higher for the remainers over theregressors for those in Action/Maintenance (time 1–2,time 2–3). These results are consistent with the TTMtheory.

Regarding the decisional balance constructs, themodel suggests that pros should increase with advanc-ing stage, while cons are expected to decrease withadvancing stage. In a cross-sectional study, Marcus andcolleagues [32] reported that pros of exercise behaviorincreased with advancing stage (7 of 10 possible pair-wise contrasts were significant) and that cons decreasedwith advancing stage (8 of 10 possible pairwise con-trasts were significant). Given that the TTM is a dy-namic model, cross-sectional study findings are inap-propriate to adequately test the model and their resultsmust be viewed with limitation. However, our morerigorous design revealed that pros and cons provideonly partial support of the decisional balance variablesin their ability to predict stage transition, which is alsoconsistent with the limited performance of these exer-cise decisional balance constructs in other exercise TTMstudies [41,33].

We found pros significantly higher for those who re-mained in Action or Maintenance (time 2–3) than forthose who regressed and that they predicted forward

movement from Precontemplation (time 2–3) and Con-templation (time 1–2, time 2–3). Lower con scores weresignificant predictors only for those remaining inAction/Maintenance (time 2–3) and for the forwardtransition from Preparation (time 2–3). Despite the fact

Experiential processes 2.49 (0.80) 2.55 (0.77) 2.66 (0.73) 0.46 (0.077) 0.78 0.219Behavioral processes 2.14 (0.76) 2.22 (0.74) 2.54 (0.80) 3.72* (0.217) 1.92 0.028

Note. P level is one-tailed.* P , 0.05.

*** P , 0.001.

that a number of predictions for the pros and cons didnot reach levels of statistical significance, it is notewor-thy that the means were generally in the hypothesizeddirections, with four results approaching levels of sta-tistical significance (i.e., P values ranging from 0.064to 0.083). The score differences between the pros and

the cons were also consistent with Prochaska and col-

Experiential processes 2.39 (0.78) 2.15 (0.84)Behavioral processes 2.41 (0.64) 2.31 (0.80)

Note. P level is one-tailed.* P , 0.05.

*** P , 0.001.

higher than the cons for those in Precontemplation,which is contrary to the TTM literature [12,15].

The model’s “Strong and Weak Principles of Pro-gress,” governing the pros and cons constructs, positsthat progress from Precontemplation to Action involvesapproximately 1 standard deviation (SD) increase in

EXERCISE AND THE TRANSTHEORETICAL MODEL 447

TABLE 4

Planned Contrasts of TTM Constructs for Persons in the Contemplation Stage at Times 1 and 2 Who Regressed, Remained, orProgressed from That Stage over a 6-Month Period

Stage change over 6 months

TTM Regressed Remained Progressed F (eta) t P level

Time 1–time 2 (n 5 199) (n 5 29) (n 5 74) (n 5 96)Self-efficacy 2.47 (0.62) 2.78 (0.63) 3.07 (0.70) 10.29*** (0.308) 4.29 ,0.001Pros 3.60 (1.07) 4.02 (0.66) 3.92 (0.89) 2.67 (0.164) 1.79 0.038Cons 2.20 (0.64) 2.10 (0.62) 2.00 (0.69) 1.21 (0.111) 1.43 0.077Experiential processes 2.36 (0.80) 2.60 (0.74) 2.45 (0.72) 0.99 (0.179) 0.57 0.285Behavioral processes 2.02 (0.64) 2.24 (0.65) 2.39 (0.78) 3.27* (0.118) 2.49 0.004

Time 2–time 3 (n 5 152) (n 5 16) (n 5 71) (n 5 65)Self-efficacy 2.71 (0.77) 2.94 (0.67) 3.00 (0.59) 1.37 (0.134) 1.66 0.050Pros 3.56 (1.00) 4.00 (0.71) 4.09 (0.78) 2.81 (0.190) 2.37 0.001Cons 2.25 (1.10) 2.14 (0.64) 2.05 (0.79) 0.54 (0.084) 0.96 0.171

the pros for changing (strong principle) and approxi-

mately a 0.5-SD decrease in the cons (weak principle)league’s cross-sectional study data (for 12 different be-

haviors) in which the pros of changing were higher [12,15]. An examination of the study’s main results,along with the means and standard deviations of thesethan the cons for people in Action/Maintenance [12,15].

However, our study also reported that the pros were constructs across the stages, does not provide direct

TABLE 5

Planned Contrasts of TTM Constructs for Persons in the Preparation Stage at Times 1 and 2 Who Regressed, Remained, orProgressed from That Stage over a 6-Month Period

Stage change over 6 months

TTM Regressed Remained Progressed F (eta) t P level

Time 1–time 2 (n 5 97) (n 5 27) (n 5 23) (n 5 47)Self-efficacy 3.01 (0.49) 3.09 (0.60) 3.23 (0.67) 1.19 (0.158) 1.49 0.070

Pros 4.01 (0.95) 3.66 (0.91) 4.00 (0.81) 1.31 (0.164) 0.06 0.478Cons 2.16 (0.82) 1.78 (0.57) 1.97 (0.68) 1.87 (0.195) 1.17 0.122Experiential processes 2.40 (0.74) 1.92 (0.59) 2.45 (0.80) 4.39* (0.301) 0.27 0.393Behavioral processes 2.72 (0.74) 2.13 (0.68) 2.63 (0.77) 4.70* (0.292) 0.52 0.304

Time 2–time 3 (n 5 83) (n 5 36) (n 5 21) (n 5 26)Self-efficacy 2.74 (0.69) 3.00 (0.56) 3.44 (0.69) 8.44*** (0.417) 4.10 ,0.001Pros 3.78 (0.98) 3.54 (0.95) 4.15 (0.89) 2.54 (0.245) 1.54 0.064Cons 2.12 (0.72) 2.08 (0.50) 1.81 (0.55) 2.09 (0.224) 1.96 0.030

2.60 (0.89) 1.65 (0.200) 0.97 0.1672.60 (0.82) 0.96 (0.152) 1.01 0.158

Pros 3.94 (0.85) 4.22 (0.80) 3.04 0.002

Cons 1.93 (0.69)Experiential processes 2.47 (0.68)Behavioral processes 2.75 (0.70)

Note. P level is one-tailed.

support for this principle. However, consistent with themodel, pros scores were significantly (P , 0.05) higherfor those individuals in Action/Maintenance than thosein Precontemplation, while cons scores were signifi-cantly (P , 0.05) lower for those in Action/Maintenancethan for those in Precontemplation.

Our results concerning processes of change provideminimal support for the general predictions of themodel. In addition, our findings are different from those

reported by Marcus and colleague’s worksite study in

Behavioral processesTime 1–2 Higher NC Higher HigTime 2–3 Higher Higher Higher Hig

Total correct predictions 3/10 6/

Note. NC, no change; Higher, higher score; Lower, lower score.

1.63 (0.62) 4.01 0.0002.63 (0.72) 2.01 0.0233.03 (0.74) 3.46 0.001

one of the experiential processes (dramatic relief) scoressignificantly declined over the 6-month period with thestudy’s 37 relapsers [16].

In terms of the global (aggregated) and specific expe-riential processes, our study found that those who re-mained in Action/Maintenance had higher experientialprocesses scores than those who regressed (time 2–3),which indicates that the experiential processes remainsalient in the latter stages. This finding coincides with

448 PLOTNIKOFF ET AL.

TABLE 6

Comparison of TTM Constructs for Persons in the Action/Maintenance Stages at Times 1 and 2 Who Regressed or Remained inThose Stages over a 6-Month Period

Stage change over 6 months

TTM Regressed Remained t P level

Time 1–time 2 (n 5 309) (n 5 83) (n 5 226)Self-efficacy 3.34 (0.69) 3.59 (0.68) 2.93 0.002Pros 4.04 (0.79) 4.19 (0.81) 1.41 0.083Cons 1.79 (0.76) 1.65 (0.66) 1.53 0.064Experiential processes 2.53 (0.81) 2.61 (0.71) 0.85 0.199Behavioral processes 2.76 (0.81) 2.97 (0.74) 2.19 0.015

Time 2–time 3 (n 5 354) (n 5 113) (n 5 241)Self-efficacy 3.35 (0.63) 3.64 (0.62) 4.06 ,0.001

the Project Active Trial in which experiential processes

which a small subsample of 63 adopters reported sig- were positively associated with those individuals

achieving recommended activity levels [29]. However,nificantly higher experiential and behavioral processesscores (with the exception of social liberation) at 6 contrary to TTM, the experiential processes in our study

had no effect in the early stages of stage transitions,months [16]. Further, all the behavioral processes and

TABLE 7

Summary of TTM Tested Hypotheses to Predict Forward Stage Transition over Two Time Periods

Precontemplation Contemplation Preparation Action/MaintenanceSupported

Hypothesis Result Hypothesis Result Hypothesis Result Hypothesis Result Hypotheses

Self-efficacyTime 1–2 Higher NC Higher Higher Higher NC Higher Higher 6/8Time 2–3 Higher Higher Higher Higher Higher Higher Higher Higher

ProsTime 1–2 Higher NC Higher Higher Higher NC Higher NC 4/8Time 2–3 Higher Higher Higher Higher Higher NC Higher Higher

ConsTime 1–2 Lower NC Lower NC Lower NC Lower NC 2/8Time 2–3 Lower NC Lower NC Lower Lower Lower Lower

Experiential processesTime 1–2 Higher NC Higher NC Higher NC Higher NC 1/8Time 2–3 Higher NC Higher NC Higher NC Higher Higher

her Higher NC Higher Higher 5/8her Higher NC Higher Higher10 2/10 7/10 18/40

N

EXERCISE AND THE TRA

on which they are posited to be more influential thanthe behavioral processes [12].

The finding that the global (and specific) behavioralprocesses for those who remained in Action/Mainte-nance (time 1–2, time 2–3) would have higher behav-ioral scores than for those who regressed is consistentwith the model. The global (and specific) behavioralprocesses also predicted transition from Precontempla-tion (time 2–3) and Contemplation (time 1–2, time 2–3). TTM posits that the behavioral processes are utilizedmore in Action and Maintenance than the preactionstages and experiential processes are emphasized inthe preaction stages [12,42]. It is interesting to notethat the behavioral processes (and not the experientialprocesses) were instrumental in the preaction stages.Herzog and researchers also found the behavioral proc-esses to predict movement out of the Precontemplationand Contemplation stages in their prospective study onsmoking cessation [26]. In sum, it may be worthwhileto place a stronger emphasis on the use of behavioralprocesses over experiential processes for those in preac-tion, which is in contrast with a recent meta-analysisof 47 cross-sectional studies in which it was reportedthat: (1) in smoking cessation, experiential processeswere used more in earlier stages than were behavioralprocesses and (2) in exercise adoption and diet change,the use of behavioral and experiential processes in-creased together [43].

Our study revealed some counterintuitive findingsfor both the experiential and the behavioral processesof change in the Preparation stage. Tukey post hoc test-ing on significant F tests that did not yield a significantt result for the planned contrasts revealed that thosein Preparation (time 1–time 2) who progressed andthose who regressed had significantly (P , 0.05) higherexperiential and behavioral processes scores than thosewho remained in this stage. A potential explanation forthis unexpected result is that during this tenuous stagewhen individuals are somewhat ambivalent about exer-cise, they may make a conscious decision about whetherto continue to exercise. A further explanation for thisfinding may be attributed to the criteria specified fordefining Preparation. Preparation for exercise behaviorincludes the term “regular” (defined as three or moretimes/week). There may be some stage misclassificationas the Preparation stage for exercise also includes in-tensity and duration parameters, making this stageconceptually and empirically arduous to reliably clas-sify. Regardless, Preparation appears to be a criticalstage in the behavior stage continuum, which needsmuch more exploration.

Prochaska and Velicer [12] acknowledge the complex-ity and challenge of integrating the process of changeconstructs within the stage model and that this tenetof TTM has received the least empirical support of themodel. Given that TTM’s processes of change constructs

STHEORETICAL MODEL 449

had their origins in smoking behavior, which may notbe directly transferable to exercise, along with Herzogand colleagues’ lack of support for the processes in thesmoking domain [24], it is not overly surprising thatmany of our processes results were inconsistent withthe model.

The effect sizes (r) throughout the study ranged from0.077 (small) to 0.417 (medium) as determined by Co-hen [40], with all medium effect sizes reported to besignificant. Power to detect medium effect sizes was.0.70. Therefore the null results were not due to a lackof statistical power. Despite employing a liberal a (P ,0.05) to examine the internal validity of TTM (as justi-fied in other studies [26,44]) the overall results yieldat best moderate support to predict progressive stagetransition. There was a greater amount of nonsup-portive results (22/40) than supportive findings (18/40).(Assuming each hypothesis is independent, one couldexpect two false positive and two false negative resultsby chance alone, i.e., P 5 0.05 3 40 tests.) Further, twocounterintuitive results (i.e., experiential and behav-ioral processes in the Preparation stage) were reported.Taken together, this calls into question the appropriate-ness of the model to predict exercise behavior change.Further, there was a lack of consistency of the predictivenature of TTM’s constructs in our population betweenthe two separate time periods. Despite the support ofTTM’s internal validation produced in cross-sectionalstudies across various behaviors [12], it appears thatthe more sophisticated designs (i.e., prospective cohortstudies) that test the model are unable to replicate someof these findings. For example, in the recent prospectivetest of TTM in the smoking domain, Herzog and col-leagues reported that the processes of change and thepros and cons of the behavior did not predict progressivemovement out of the Precontemplation, Contemplation,or Preparation stages at both 1- and 2-year follow-ups[26]. While the Herzog study measured only 6 of the10 processes of change and did not assess self-efficacy,their numerous null results of the model’s internal vali-dation are concerning as only 1 of 120 statistical testssupported the ability of the TTM constructs to predictstage movement [26].

There are a number of issues that need to be consid-ered in understanding the implications of our findings.In terms of predictors for forward stage progression,Bandura’s self-efficacy [77] appeared to be the strongestconstruct of the TTM, while experiential processes wasthe weakest predictor. Self-efficacy has consistentlybeen reported to be strongly associated with exercise[46] and other health behaviors [47]. Indeed, this con-

struct has been incorporated into a number of social–cognitive models (e.g., Social Cognitive Theory, Protec-tion Motivation Theory, Health Belief Model). In termsof stage, the TTM constructs provided the strongestsupport in the Action/Maintenance stage retention,

O

450 PLOTNIK

with limited impact on progression from the Precontem-plation and Preparation stages. These results challengethe underlying theoretical underpinnings of the modelin addition to having implications for practitioners whoare currently using the model in exercise stage-matchedinterventions, as a significant proportion of the adultpopulation are in preaction stages. Other social–cognitive variables may need to be considered to furtherexplain forward stage transition out of the preactionstages. In particular, an earlier study from this samepopulation reported that the Theory of Planned Behav-ior constructs of attitude and subjective norm with so-cial support significantly predicted stage transitions inthe preaction stages [25].

TTM may be a useful heuristic; however, the specific-ity of the model may need to be modified to matchthe behavior of interest. Our results provide directiontoward the testing of future intervention trials in theexercise domain. Despite some of the study’s limitedempirical findings, it is important to view our resultsin context of other current social–cognitive models ofhealth behavior change, in which the ability of thesetheories and models to explain health behavior change(e.g., exercise behavior) is also of limited magnitude[7,48–50].

Methodologically, the stage of change algorithm maybe a limited measure of motivation to adhere to physicalactivity recommendations; the 6-month markers in thestaging algorithm are arbitrary for this behavior. Fur-ther, the current definition of Preparation for exercisebehavior may be invalid.

Despite the methodological strengths that this studyundertook (e.g., the randomized population-based sam-ple, longitudinal cohort design, rigorous validation ofthe mediating measures, and the examination of theresults by possible age, sex, and physical health/disability/injury confounders) there are a number oflimitations of the study that need to be acknowledged.First, this study employed the short-form experientialand behavioral processes (2 items per subfactor) ratherthan the traditional 4 items per scale, which may havecompromised the reliability of these measures. How-ever, short-form instruments to measure the TTM proc-ess constructs are commonly employed in larger popula-tion- and community-based studies [26]. Second, theremay be a seasonal variation associated with these re-sults as exercise behavior patterns among Canadianscan vary according to season [51]. Cognitions and be-haviors of the participants may have been influencedby the contrasting summer and winter temperatures

experienced in the geographical location of the studycatchment area. Third, while this study is the first TTMresearch attempting to sample a representative popula-tion, the modest response rate yielded a sample higheron socioeconomic indicators than the normal Canadian

FF ET AL.

population, which may limit the generalizability of thefindings to the general adult population.

Further TTM research in the exercise domain isneeded to examine a number of important issues. First,there is a need to replicate similar longitudinal, popula-tion-based studies to examine the internal validity ofTTM in the exercise domain along with other healthbehaviors with the general population.

Second, theoretical integration of further constructsfrom other social–cognitive models toward a modifiedTTM or such other integrated approach is worthy ofinvestigation. We may do well to build upon the currentstrengths empirically supported by the model in addi-tion to specifically examining other social–cognitiveconstructs to predict stage transition especially in thepreaction stages [25,44]. Indeed, the authors of thispaper are currently undertaking such work based onthe results of this data set, which include measuresfrom the Theory of Planned Behavior, Protection Moti-vation Theory, Social Learning Theory, and Health Be-lief Model, to build and test stage models based ontheoretical and empirical grounds [25]. However, it isvery clear from our research that self-efficacy is thestrongest construct in stage advancement; researchersand practitioners should ensure that their work in-cludes this pivotal tenet.

Third, there is a need to develop and test furthertheory on the interrelationships among the TTM medi-ating constructs. TTM offers theoretical predictions be-tween the independent constructs and the dependentconstruct (i.e., stage), but does not offer explicit theoret-ical predictions concerning the relationships among theindependent constructs [52]. To date, Prochaska hasnot articulated the relationships among the processesof change, self-efficacy, pros, and cons [52].

Finally, from a public health perspective it is im-portant to assess moderate levels of activity [53]. Whiletheory testing to date has primarily focused on exercise(i.e., vigorous physical activity), future TTM researchshould include both vigorous and moderate staging lev-els and corresponding cognitive constructs reflectingboth levels of activity.

In conclusion, there are too few rigorous prospectivedesigns in the TTM domain to make any definite conclu-sions about the robustness of the model’s internal valid-ity to predict exercise behavior. However, given the pop-

ularity of TTM for public health programs related tophysical activity, our findings of the theoretical testingof TTM will hopefully guide further direction to social–cognitive theory researchers, health and medical prac-titioners, and health planners.

ACKNOWLEDGMENTS

The project was initiated and analyzed by the study’s investigators.The authors acknowledge the work of Ryan Rhodes, Ph.D., LynneLeonard, Ph.D. (Cand.), Janice Hansen, Ph.D., Cameron Wild, Ph.D.,

EXERCISE AND THE TRAN

Allan Fein, M.Sc., and John Spence, Ph.D., for their contributions tothis research.

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