1. Mediators and moderators of physical activity maintenance: a systematic review.
Jennifer Murray1, Dr. Sarah Brennan1, Prof David French2, Prof Chris Patterson1, Prof Frank Kee1, Dr. Ruth Hunter1
1UKCRC Centre of Excellence for Public Health, Queen's University Belfast, UK, 2School of Psychology, University of Manchester, UK

2. Background Physical activity health benefits require maintenance.
Interventions achieve short-term change, with new behaviours rarely maintained.
Understanding effective mediators and moderators of physical activity maintenance can help unpick causal mechanisms and inform future interventions.

3. Definitions Mediators:
Intervening variables (psychological, social or environmental) in the causal process or pathway between the intervention and effect (Baron & Kenny, 1986).
Causal steps (e.g. Baron and Kenny, 1986)
Difference-in-coefficients (e.g. McGuigan and Langholtz, 1988)
Product-of-coefficients (e.g. MacKinnon and colleagues, 2004). a b c

4. Definitions Moderators:
Variables (usually pre-test, e.g. age, gender, socio-economic status) for which the strength of the relationship between the intervention and effect varies (Baron & Kenny, 1986). I I I

5. Behaviour change maintenance:
Maintenance occurred six months post-baseline. Lenient definition of behaviour change maintenance derived from the Transtheoretical Model of behaviour change (Prochaska & DiClemente, 1982).

6. Aims
Mediators: intervention effects on mediators, mediator effects on PA outcomes and whether a mediating link was established.
Moderators: effects of moderators and whether interventions were more effective for certain study characteristics or for certain subgroups of participants.
Appraisal of methodological quality of mediation and moderation analyses.

7. Methods Search strategy: Eligibility criteria: Databases:
Physical activity
Study design
Maintenance
Behaviour change
Databases:
MEDLINE, EMBASE, PsycINFO, CINAHL, Cochrane database & Web of Science
Eligibility criteria:
Population
Intervention
Comparison
Outcomes

8. Search results Database searching (n=6,712) Manual searching (n=302)
Records screened
(n=5,032)
Full texts screened
(n=348)
Articles included
(n=69, 38 separate studies)
26 mediators, 18 moderators

9. Individual-level processes: Feelings
Mediators ≥6 months
Revitalisation
(n=12/12)
Tranquillity
(n=2/8)
Enjoyment
(n=2/18)
Individual-level processes: Feelings
Mood
(n=0/3)
Physical exhaustion
(n=2/8)
Severity
(n=0/3)
Fear
(n=0/3)
Vulnerability
Positive attitude
(n=0/2)

10. Individual-level processes: awareness/adherence
Mediators ≥6 months
Awareness of intervention
(n=1/1)
Intervention adherence
(n=1/1)
Physical activity awareness
(n=5/11)
Individual-level processes: awareness/adherence
Habit
(n=1/1)
Self-concept
(n=5/5)
Intentions
(n=7/15)
Positive engagement
(n=1/8)
Commitment
(n=1/11)
Beliefs about benefits
(n=1/9)

11. Individual-level processes: Skills
Mediators ≥6 months
Self-management
(n=2/3)
Self-regulatory skill use
(n=2/5)
Planning (strategic)
(n=2/12)
Individual-level processes: Skills
Coping planning
(n=0/10)
Planning (action)
(n=1/10)
Perceived behavioural control
(n=0/3)
Goal setting
(n=1/6)

12. Individual-level processes: TTM variables
Mediators ≥6 months
Cognitive processes of change
(n=13/25)
Behavioural processes of change
(n=16/25)
Mean stage of change
(n=0/3)
Decisional balance
(n=6/20)
Pros
(n=2/4)
Cons
(n=0/3)
Individual-level processes: TTM variables
Motivational readiness
(n=0/2)
Outcome expectations
(n=3/19)
Exercise self-efficacy
(n=13/47)

13. Social/environmental variables
Mediators ≥6 months
Instrumental or institutional social support
(n=1/4)
Friends/community social support
(n=4/15)
Family social support
(n=4/11)
Social/environmental variables
Injunctive norms
(n=0/3)
Descriptive norms/social modelling
Social influences
(n=0/1)
Social support
(n=4/22)
Exercise perceived barriers
(n=6/28)
Perceived environment
(n=1/11)

14. Interventions favoured
Moderators ≥6 months
Interventions favoured
Baseline enjoyment (n=2/2), baseline activity (n=5/9), age (n=3/6), stage of change (n=1/3), baseline health status (n=1/3), BMI (n=1/3), environment (n=1/4), education (n=1/6), gender (n=3/15), intervention dose (n=1/2), intention (n=1/1).
No evidence
Household income (n=0/2), employment status (n=0/2), ethnicity (n=0/2), physiological response (n=0/2), perceived pain (n=0/2), marital status (n=0/1), self-efficacy (n=0/1), social support (n=0/1).

15. Conclusions
Effective mediators ≥ 6 months were revitalisation, self-concept and the behavioural processes of change.
Mediators should be measured at longer time-points.
8/26 studies carried out formal mediation tests. 10/18 studies investigated moderators by subgroup analyses.
Formal mediation tests should have an explicit theoretical rationale.
Mediators and moderators should be considered together.