Exercise habit strength, planning and the theory of planned behaviour: an action control approach

Objectives
Action control refers to the successful translation of intention into behaviour. The purpose of this study was to explore the potential usefulness of extending intention-exercise profiles with past exercise behaviour and exercise habit strength and the potential discriminative effect of action planning items and theory of planned behaviour (TPB) concepts.

Design
Prospective data from 330 undergraduate students (M age = 21.5; 25.5% males).

Method
Measures of exercise behaviour, exercise habit strength, TPB concepts and action plans were assessed at T1; subsequent exercise behaviour was assessed again two weeks later. Profiles were created from T1 exercise behaviour, intention, habit strength and T2 exercise behaviour. Data were analyzed using chi-square analysis, discriminant function analysis and analysis of variance and interpreted using p-values and effect sizes.

Results
There was considerable asymmetry in the intention-exercise relationship, with successful exercise intenders reporting stronger exercise habits. However, more than 40% of strongly habitual exercise intenders were not following on these intentions. Measures of perceived behavioural control were the consistent predictor of action control, but could not discriminate differences between key target groups. Effect sizes for significant differences were mostly large. Planning items were generally unrelated to exercise action control.

Conclusion
The extension of intention-exercise profiles revealed noticeable distributions to allow for better exercise target group detection. Measures of controllability of exercise behaviour should be promoted in several of these target groups, but research should explore additional predictors of key target groups in order to enhance exercise levels.