The effects of persuasive communication and planning on intentions to be more physically active and on physical activity behaviour among low-active adolescents.

The purpose of the present study was to examine, using the theory of planned behaviour (TPB) combined with a self-regulatory behaviour change approach, whether persuasive communication based on adolescents' salient beliefs (SBCondition) and planning (PCondition) could promote the intention and physical activity (PA) behaviour of low-active adolescents participating in less than 1 h/day of moderate-to-vigorous physical activity. The protocol tested the effectiveness of two strategies used separately (i.e. SBC or PC) or in combination (i.e. CC = NSBC-SBC-PC) compared to a group receiving a message based on non-salient beliefs (NSBCondition). The 116 low-active students from ten 10th and 11th grade classes were assigned, using a cluster randomisation, into one of the four conditions (i.e. NSBC, SBC, PC and CC). Baseline data were collected two weeks before the intervention. The post-test data collection occurred directly after the intervention, and the follow-up took place two weeks later. Results showed that (1) the NSBC was the least effective strategy, (2) the SBC had no significant effect on PA behaviour and the TPB variables, (3) the PC had no significant effect on PA behaviour but increased the intention and perceived behavioural control and (4) the effects of the PC and the CC were not significantly different.