Table 2.

Theoretical perspectives

	Diffusion of innovations [70, 95]	Complexity theory/complex systems theory [71]	Ecological theory [72, 96]	General systems theory or open systems theory [73]
No. of approaches drawing on theory	10	9	5	4
Sustainability process	Sustainability is viewed as the final stage of initiative life cycle [18, 86]	Sustainability is a nonlinear process where change, adaptation and uncertainty are expected [15, 31, 53, 68]	Views sustainability as an ongoing and dynamic process that occurs throughout implementation [11, 72]	Sustainability is a process where things can return to the norm (‘homeostasis’) or adapt to the environment to survive. [85, 92]
Theory application in approaches	This perspective explores how programme benefits and burden will support or be a barrier to sustainability [54, 66]. Within approaches using this perspective, the role of adopters of the initiatives were seen as key to success, specifically to achieve wider reach during initiatives and maintain activities after the initiatives come to an end [27].	This perspective highlights how the interactions that occur between an initiative, the setting, the broader organisation and the sociocultural context impact sustained change. Initiatives were viewed as components being introduced to complex adaptive systems that change and adapt in response to interactions with the environments, individuals and wider context [53].	This perspective focuses on behaviour and how it is influenced by and influences individuals and environments [72] Approaches adopting this perspective focused on the need to find the right fit between initiatives, contexts and expectations to inform the ongoing adaptation of initiatives to achieve sustainability [11]	This perspective views an organisation as an organism open to the influence of its environment with the need to adapt to survive in order to achieve lasting change [73] Approaches using this perspective explored perceived benefits and burden of an initiatives, availability of support for initiatives and leadership within organisations [54]