This paper presents a discussion of the development of a middle-range nursing theory of the effects of music on physical activity and improved health outcomes.

Background. Due to the high rate of physical inactivity and the associated negative health outcomes worldwide, nurses need new evidence-based theories and interventions to increase physical activity.

Data sources. The theory of music, mood and movement (MMM) was developed from physical activity guidelines and music theory using the principles of statement and theory synthesis. The concepts of music, physical activity and health outcomes were searched using the CINAHL, MEDLINE, ProQuest Nursing and Allied Health Source, PsycINFO and Cochrane Library databases covering the years 1975–2008.

Discussion. The theory of MMM was synthesized by combining the psychological and physiological responses of music to increase physical activity and improve health outcomes. It proposes that music alters mood, is a cue for movement, and makes physical activity more enjoyable leading to improved health outcomes of weight, blood pressure, blood sugar and cardiovascular risk factor management, and improved quality of life.

Conclusion. As it was developed from the physical activity guidelines, the middle-range theory is prescriptive, produces testable hypotheses, and can guide nursing research and practice. The middle-range theory needs to be tested to determine its usefulness for nurses to develop physical activity programmes to improve health outcomes across various cultures.