This study aimed to determine the usefulness of integrating basic psychological needs theory (BPNT) and relational frames theory (RFT) in order to explain the effects of social physique anxiety (SPA) - in the context of exercise - on exercisers' mental health. A total of 296 recreational cyclists and triathletes (100% males) aged 18 to 60 years old (M age = 35.65, SD = 9.49) completed a multi-section questionnaire assessing the target variables. Two models of structural equations with multiple mediators were tested using 5000 bootstrap samples. While the BPNT-based model explained 20% of variance in satisfaction with life (SWL) and 25% of variance in mental health (MH), the model that also incorporated RFT explained 43% of variance in both of those variables. Results showed that SPA negatively impacted exercisers' mental health via two different mechanisms: a) through a decrease in perceived satisfaction of basic psychological needs (β = -.05, p = .045 for SWL; β = -.07, p = .002 for MH); b) through an increase in psychological inflexibility, generated directly by SPA (β = -.24, p < .001 for SWL; β = -.20, p < .001 for MH) and also mediated by basic psychological need thwarting (β = -.09, p < .001 for SWL; β = -.08, p = .002 for MH). Results supported integrating the two theories, elucidating the processes by which a controlling social factor like SPA can affect the potential benefits of exercise.
Keywords: basic psychological needs; exercise; mental health; psychological inflexibility; social physique anxiety.