Habit and physical activity: Moderation and mediation studies in older habits

It is well-established that for older adults a physically active lifestyle is highly beneficial for health. Public health guidelines state that all adults should be at least moderately physically active for at least 30 minutes per day on at least five days per week. Unfortunately, a large proportion of older adults do not meet this physical activity (PA) recommendation. These older adults are insufficiently physically active to obtain the health benefits associated with regular and sufficient PA. Promoting PA in older adults istherefore of major relevance. Development of effective interventions to promote PA relieson insight into the determinants of PA and their working mechanisms. A determinantthat merits examination in this regard is habit. The potential importance of habit lies inits close ties to PA maintenance, which, in turn, is essential for obtaining many healthbenefits. Although research has already revealed that PA has a habitual component, thelongitudinal relationship between habit and PA can still be unraveled in more depth.The aim of this thesis is to contribute to a more comprehensive understanding of habit’srelation to PA. This understanding may inform intervention development.Chapter 1 describes the concept of habit, provides a brief history of habit from apsychological perspective, and defines PA for all studies in this thesis as the number ofdays per week on which a participant was at least moderately physically active for atleast 30 minutes. Furthermore, this chapter describes that in health psychology for yearsthe dominant approach has been to consider health behavior the result of a conscious,explicit, rational decision making process. This approach is known as the social cognitiveapproach. However, a more complete account of behavior can be achieved when inaddition to explicit cognitions, such as intentions and attitudes, implicit processes, suchas habits, are recognized. Models that account for both explicit, conscious influencesand implicit, unconscious processes on behavior are called dual-process models. Thefirst two studies of this thesis are concerned with PA as the outcome of a dual-process.The third and fourth study of this thesis test several mediation effects in which habitand PA play several roles. Chapter 1 specifies the research questions of the studies in thisthesis in detail. All studies are conducted in older adults, aged 50 years or older.Chapter 2 presents a study that examined whether habit strength moderates theintention-physical activity (PA) relationship within the framework of the theory ofplanned behavior (TPB) and the attitude-social influences-efficacy (ASE) model. Alongitudinal design with two measurement points was applied. Three PA habit groupswere composed: a low, a medium, and a high PA habit group. The results of structuralequation modeling (SEM) analyses showed that intention only significantly determinedPA in the low and medium PA habit groups, implying that PA was not intentional at high levels of habit strength. Habit operated as a moderator of the intention-PArelationship. It is therefore recommended to add habit to the TPB/ASE model. Thiswould transform this social cognitive model into a model that has characteristics of adual-process model. As strong habits may limit the potential to change PA intentionally,only applying persuasive messaging as an intervention strategy may not suffice, andadditional intervention strategies are needed for strongly habitual, but insufficientlyactive older adults.Chapter 3 shows a study that targeted the question why prior PA is a good predictorof later PA, even after TPB/ASE variables have been taken into account. This questionis known as the residual variance problem. It has been suggested that habit operatesas a mediator between prior and later behavior and as such forms at least a partialsolution to the residual variance problem. In other words, prior behavior is proposedto exert its influence on later behavior through habit. This proposition was tested usinga longitudinal design with four measurement points. Path analyses showed that habitindeed significantly mediated the relationship between prior and later PA, after TPB/ASEvariables were taken into account. This result indicates that habit is a partial solutionto the question why prior PA is a good predictor of later PA. It is recommended toincorporate habit into the TPB/ASE model.Chapter 2 and 3 both present studies that recommend to add habit to the TPB/ASEmodel. In these two chapters habit appears in two different roles: as a moderator thatis concurrently assessed with intention, and as a post-intentional predictor of PA. Bothroles not only indicate that habits have to be taken into account when explaining andpredicting PA and when designing PA interventions based on the TPB/ASE model, butalso that habit is a relevant construct in different phases that precede PA. The studiesindicate that there is reason to consider incorporating habit into the TPB/ASE model inboth roles. Both studies modeled habit as a variable that precedes PA. Additional insightinto habit’s relation to PA can be achieved by modeling PA as a variable that precedeshabit. In both Chapter 4 and 5 PA appears as a variable that affects habit.Chapter 4 reports on a study that applied a cross-lagged panel design to examinewhether habit mediates the relationship between prior and later PA and whether PAsimultaneously mediates the relationship between prior and later habit. The hypothesisthat both mediation effects occur simultaneously was tested in two independentsamples of older adults. While a significant PA-habit-PA path would support the implicitassumption underlying many PA interventions that PA sustains over time through habit,a significant habit-PA-habit path would indicate that PA interventions could benefitfrom incorporating habit formation strategies. The results of SEM analyses were not unambiguous. Indications for the existence of both hypothesized mediation effectswere found, but no clear, unequivocal pattern appeared. Somewhat more supportwas found for the PA-habit-PA path than for the habit-PA-habit path. More research isneeded to draw more definitive conclusions.Chapter 5 presents a study that modeled habit as an outcome variable. Habit formationhas been proposed as a way to ensure long-term maintenance of PA and, as such, asa desired outcome of PA interventions. Intention, action planning (AP), and PA aresuggested to be determinants of PA habits. It is, however, largely unknown how theydetermine PA habits. In two independent samples of older adults, the hypothesis wastested that the relationship between intention and habit is mediated by AP and/or PA. Afour-wave longitudinal design was used. SEM analyses showed significant intention-PAhabitpaths and nonsignificant intention-AP-habit and intention-AP-PA-habit paths inboth samples. Thus, the relationship between intention and PA habit was mediated byPA and intention was neither associated with habit via AP as a single mediator, nor viaAP and PA as sequential mediators. Possible conditions under which intention-AP-habitpaths and intention-AP-PA-habit paths exist are discussed in detail.Chapter 6 provides a summary and discussion of the main findings of the studies inthis thesis, discusses methodological issues, and indicates implications for practiceand directions for future research. A major strength of the studies in this thesis is thestudy population of older adults. Older adults are an underrepresented populationin habit research. In light of both the rapid growth of this population and the largeproportion of insufficiently physically active older adults, it is relevant to target olderadults in PA habit research. Other major strengths are the large number of participants,the longitudinal design with four measurement points, and the use of two datasetsin two studies. Limitations include the considerable and selective dropout and themeasurement of PA by self-reports. The strengths and limitations should be takeninto account when interpreting the findings of this thesis. Important implications forpractice are that existing habits have to be taken into account when developing PApromotion interventions for older adults based on the TPB/ASE model, and that it maybe worthwhile to incorporate habit formation strategies, such as the use of remindersand self-monitoring, into interventions to improve the translation of PA into PA habits.An important direction for future research consists of close replications of the studies inthis thesis as well as replications with variations in study population, time intervals, andtarget behavior. Other directions for future research include conducting experimentaltests of the efficacy of habit formation strategies, gaining insight into the process ofhabit formation for different age groups, and testing the stability and development ofhabit over time.To conclude, this thesis shows that habit and PA are longitudinally connected witheach other in several ways; there is continuous, reciprocal influence between habitand PA. Habits have to be taken into account when explaining, predicting, influencing,and maintaining PA. Being sufficiently physically active is associated with many healthbenefits. Through their influence on PA, habits for sufficient PA contribute to obtainingthese health benefits.