Electronic Thesis and Dissertation Repository


Doctor of Philosophy


Health and Rehabilitation Sciences


Dr. Jennifer Irwin

2nd Supervisor

Dr. Don Morrow

Joint Supervisor



The primary purpose of this dissertation was to examine Motivational Interviewing (MI) using Co-Active life coaching (CALC) skills as an intervention for individuals struggling with obesity. The secondary purpose was to investigate the characteristics of the interventionists, the Certified Professional Co-Active Coaches (CPCCs).

Study 1 quantitatively assessed the immediate and six-month-post intervention impact of receiving six-months of MI, administered via CALC skills, on weight and waist circumference and psycho-social outcomes of eight women struggling with obesity. Study 2 qualitatively assessed participants’ and the volunteer CPCC’s experience of the intervention. The purpose of Study 3 was to develop a comprehensive, applied coaching profile using a global sample of CPCCs (n=390). To expand on the characteristics of CPCCs, Study 4 explored the reasons CPCCs enjoyed their work as coaches.

In Study 1, weight decreased for all participants by the end of the intervention. At six-months follow-up, four participants continued to decrease or maintain their weight-loss. Post-intervention, participant effect sizes for the psycho-social outcomes indicated clinically significant improvements.

In study 2, participants attributed a variety of insights, and esteem and coping improvements to the intervention. The CPCC identified the most frequently used and influential strategies during sessions and suggestions for future interventionists.

Study 3’s results revealed that all participating CPCCs came from pre-existing professional backgrounds, the majority had a college degree or equivalent, and half were part-time coaches. Online referral services were not deemed useful; CPCCs did not attend the annual ICF conference; and they did not use research in their practices.

Study 4’s findings were that witnessing clients change their lives, the sense of satisfaction and fulfillment from coaching, the collaborative relationship with clients, the autonomy and flexibility of the profession, and the gratification received from using their skill set were the main reasons CPCCs enjoyed coaching.

MI via CALC skills was effective in aiding individuals fighting obesity. The profile of CPCCs provided baseline information needed to forward research that evaluates coaching services and in turn, contributes to the growing body of information needed to advance the professional field of coaching.

Keywords: Co-Active life coaching, Motivational Interviewing, Obesity, Life coaches, Behaviour change