Exploring working mechanism of an implementation strategy bundle on the implementation of a lifestyle intervention for community-dwelling older adults: process evaluation of a stepped wedge trial

Abstract

Background

A theory- and practice-based implementation strategy bundle (ISB) was developed to support physical therapists and dieticians during implementation of the combined lifestyle intervention ProMuscle for community-dwelling older adults in multiple community-care settings. Alongside a 42-week hybrid type III stepped-wedge randomized cluster implementation effectiveness trial, a process evaluation was conducted to explore possible working mechanisms of the ISB on the adoption, reach, and fidelity of ProMuscle by describing a causal pathway. Additionally, barriers and facilitators for the use of the ISB were identified.

Methods

During the 6-week transitional period in which clusters transitioned from the control to the intervention group and at the end of the 42-week trial, (group)interviews were held with physical therapists and dieticians. Interview guides were informed by the RE-AIM framework and supplemented with quantitative data from surveys and ISB tracking activity. Interviews were transcribed and thematically analyzed. Insights from the process evaluation informed a causal pathway diagram and the identification of barriers and facilitators for the use of the ISB.

Results

Twenty-five physical therapists and dieticians were interviewed during the transitional period, and fifteen participated in the group interviews at the end of the trial. The causal pathway diagram revealed that individual factors (knowledge and beliefs about the intervention, convincing others, and networking), and organizational- and system-level factors (facilitation, collaboration, and support) moderated the influence of the ISB on the implementation outcomes. Particularly organizational and system-level factors could not always be addressed by individual professionals. The fidelity of the ISB was low, according to the healthcare professionals, due to timing of receiving the ISB and lack of education on its use.

Conclusion

The results highlight the complexity of real-world implementation in multiple community-care settings and address the need for organizational and policy-level facilitation to enhance the implementation, sustainment, and scale-up of lifestyle interventions for community-dwelling older adults. Additionally, low fidelity of the ISB probably contributed to the non-significant effect of the ISB on the adoption of ProMuscle. Future implementation studies should take the timely delivery of an ISB into account and provide adequate education to healthcare professionals about the use of implementation strategies.

Trial registration

ClinicalTrials.gov (NCT05672004) registered at 12/07/2022 https://clinicaltrials.gov/ct2/show/NCT05672004

Supplementary Information

The online version contains supplementary material available at https://doi.org/10.1186/s43058-026-01034-6.

Contributions to the literature.

• A process evaluation was conducted alongside a stepped-wedge implementation trial evaluating the impact of an Implementation Strategy Bundle (ISB) on adoption, reach, and fidelity of a lifestyle intervention.

• A causal pathway diagram illustrates the ISB’ working mechanism and influencing factors on implementation outcomes.

• Organizational and system-level factors moderated the influence of the ISB, emphasizing the need for complex-sensitive strategies.

• System-level barriers exceed healthcare professionals’ capacity, indicating the importance of structured organizational and policy support.

• Low strategy fidelity, due to timing and lack of education, can diminish the ISB’ impact, highlighting the importance of tailored implementation support and appropriate study design.

Background

The importance of implementation science is growing as we aim to bridge the gap between science and practice. Particularly in community-dwelling older adults, the priority to implement new evidence to enhance healthy ageing is high, given the rapidly growing ageing population [1]. Recent implementation projects, for example, those focused on fall prevention [2] and obesity [3] have yielded valuable insights. However, the results underline the complexity of implementation, which is influenced by multiple factors on multiple levels [4]. Moreover, the context in which an evidence-based intervention (EBI) will be implemented differs per setting, and every unique context needs a tailored approach to address factors that hinder successful implementation [4].

Implementation strategies are deployed to address such barriers [5]. However, identifying what strategies would work best for the specific context with a specific EBI is challenging [5, 6]. Limited understanding of how and through what mechanism implementation strategies work hampers the ability to inform and guide practice on when and in what context strategies should be used [7]. Therefore, there is a great need to explore and evaluate strategies aimed at implementing an EBI. Especially, understanding the mechanisms through which a strategy influences implementation outcomes could facilitate the body of evidence in implementation science [5, 7, 8].

This study focuses on the implementation of the EBI ProMuscle: a lifestyle intervention for community-dwelling older adults in multiple community care settings in the Netherlands. ProMuscle is a 12-week intervention that combines resistance exercise training with a protein-enriched diet. The development of ProMuscle has gone through several phases, from clinical setting to implementation setting. Research has shown its effectiveness in improving muscle mass, muscle strength, and physical functioning. In addition, it is an intervention that fits the current workflows and contributes to the prevention of accelerated muscle mass decline that inherently relates to the maintenance of older adults’ independence [9–12].

To enhance the adoption and implementation of ProMuscle we previously developed implementation strategies based on identified barriers and facilitators for implementation of a lifestyle intervention for community-dwelling older adults in community care settings [13, 14]. A systematic approach led to the development of a theory and practice-based Implementation Strategy Bundle (ISB) to support healthcare professionals (HCPs), including physical therapists and dieticians, during the implementation of ProMuscle. The ISB is offered by way of an online tool and targets multiple barriers (knowledge, costs, and internal and external networks) with multicomponent implementation strategies that can be tailored to HCPs’ contexts [14].

Subsequently, a hybrid type III stepped-wedge cluster randomized implementation effectiveness trial was conducted to investigate the impact of the ISB on the adoption (i.e. HCPs’ intention to try or employ ProMuscle in their practice), reach (i.e. number of older adults participating in ProMuscle) and fidelity (i.e. ProMuscle delivered as intended) of ProMuscle in multiple community care settings in the Netherlands [15].

To date, there are limited studies that test and describe implementation strategies’ mechanism of action. Luckily, the attention and the necessity to understand how strategies operate is a growing area in the field [16]. To gain further understanding of factors influencing the impact of the ISB on implementation outcomes [17], a process evaluation could be conducted. A process evaluation provides insights into the “black box” in implementation by exploring the how, why, from whom, in what context, and under what circumstances the intervention is effective or not. Additionally, process evaluations can clarify possible causal assumptions, assess intervention delivery, and investigate contextual influences to inform further upscaling [18]. One way to inform a process evaluation is a causal pathway diagram (CPD). In addition to applications such as matching determinants to strategies and optimizing strategies, CPDs are useful to develop causal theories [5, 7]. A CPD specifies the preconditions, mechanisms, moderators, and mediators of the strategy to represent the interrelations among variables within a specific context [5, 7]. Causal theories enable researchers to investigate whether strategies work through theorized mechanisms, how contextual factors moderate the process, and to what extent these mechanisms account for the desired implementation outcomes. For the implementation of ProMuscle, no causal theories are available. Therefore, understanding of what influences the ISB’ effect on the adoption, reach, and fidelity of ProMuscle [19] enhances the generalizability of the trial findings for scale-up and to other contexts and interventions [20].

The primary aim of the current process evaluation is: To explore possible working mechanisms by describing a causal pathway of the ISB on the adoption, fidelity, and reach of ProMuscle in multiple community-care settings. And secondary: to describe barriers and facilitators for the use of the ISB.

Method

This study is part of the PUMP-fit study (2021–2025), which aims to provide insight into the determinants and effective strategies to implement the evidence-based combined lifestyle intervention ProMuscle, focused on improving physical functioning in community-dwelling older adults in the Netherlands. Identification of determinants of implementation, development of an ISB and the feasibility of this ISB have been published elsewhere [13, 14, 21].

Study design

A process evaluation was conducted sequentially with a 42-week hybrid type III stepped-wedge cluster randomized implementation-effectiveness trial [22]. A detailed description of the setting, design, and outcomes is presented in the study’s protocol, available at: https://clinicaltrials.gov/study/NCT05672004. The process evaluation was guided by the UK Medical Research Council (MRC) framework [20] and reported in accordance with the Standards for Reporting Implementation Studies (StaRi) checklist [23] (additional file 1). Ethical approval was obtained from the medical ethics committee of UMC Utrecht (22/050).

Hybrid type III stepped-wedge cluster randomized implementation effectiveness trial overview

Between February 2023 and January 2024, a 42-week hybrid type III stepped-wedge cluster randomized implementation effectiveness trial was conducted in 30 Dutch community-care settings. The aim of the trial was to investigate the impact of the PUMP-fit ISB on the adoption, reach, and fidelity of ProMuscle among its implementers, i.e., physical therapists and dieticians. Additionally, physical functioning measures of older adults participating in ProMuscle were collected. Changes over time and between-group differences were analyzed using linear mixed models. Results of the trial showed a non-significant increase in the primary study outcome (adoption) in the intervention group (95%CI: −0.18 - 0.81; p = 0.21) compared to the control group. After 42 weeks, 33% of the HCPs had delivered ProMuscle to a total of 27 older adults. However, compliance declined over time, resulting in increased missing data [22].

The implementation strategy bundle + logic model

The co-designed theory-based Implementation Strategy Bundle consists of 20 implementation strategies. The previously identified barriers were linked to strategies based on existing evidence and theories and further developed and described in full detail [13, 14, 24]. Figure 1 presents the Implementation Research Logic model of the ISB, in which an overview of the strategies per theme and affected outcomes are described [16]. Mechanisms of change for the multicomponent strategies were based on literature and the experiences of HCPs and implementation experts. The implementation strategies were processed into a web-based implementation toolbox, which can be tailored to HCPs’ context and supports HCPs throughout their implementation process. A previous pilot study showed that the ISB and toolbox were both acceptable and feasible for supporting HCPs during the implementation [25].

Fig. 1.

Implementation Research Logic Model of the Implementation Strategy Bundle

Setting and participants

The process evaluation was conducted in and funded by the Region Foodvalley in the Netherlands. The Region Foodvalley consists of eight municipalities that aim to promote healthier and sustainable food supplies. Approximately 200 physical therapists and dieticians work in this region. A sequential sampling method from the initial effect study was used to recruit HCPs. Thirty physical therapists and dieticians working in community care settings within this region and participating in the implementation-effectiveness trial were invited for the interviews of this study.

Before the start of the hybrid type III implementation-effectiveness study, HCPs received verbal and written information about the study and provided written informed consent.

Data collection

Both individual and group interviews with HCPs were conducted to explore possible working mechanisms and factors influencing the ISB’s impact on the adoption, reach, and fidelity of ProMuscle.

HCPs were individually interviewed during the 6-week transitional period (i.e. turnover period in which clusters switched to the intervention group) by one of the two researchers (PL or BD). Individual interviews before HCPs received the ISB were conducted to gain insight into the implementation process and perceived barriers, and to inform the interview guide at the end of the study. Group interviews were held at the end of the trial (after 42 weeks). HCPs could sign up for one of the three group interviews. The group interviews were led by one researcher (PL), a second researcher (LB) acted as moderator and took notes. Group interviews were conducted to reflect on the implementation process, and to explore the possible working mechanism of the strategies of the ISB. All researchers were trained and are experienced in qualitative and quantitative research within the implementation field. Figure 2 presents the design of the trial and timing of the interviews.

Fig. 2.

PUMP-fit hybrid type III stepped-wedge randomized cluster implementation- effectiveness trial design and number of participating HCPs. Ind = individual interviews; group = group interviews. Blue cells represent the control group = implementation as usual without implementation support. White cells = transitional period in which HCP received the ISB; individual interviews. Green cells represent the intervention group = implementation strategy bundle. Purple cells = end of the trial in which three group interviews were held

The semi-structured interview guides of the (group) interviews were based on the RE-AIM framework. In addition to qualitative data gathered by the (group)interviews, the process evaluation was informed by quantitative data collected during the overarching trial. Especially, data regarding the adoption and reach were used, collected using the Provider REport of Sustainment Scale (PRESS) and self-report surveys, respectively [22]. Fidelity data of the ISB were collected from the tracking activity of the toolbox and self-report surveys. For example, the PRESS showed fluctuating scores over time. During the group interview at the end of the trial, HCPs were asked about their willingness and attempts to adopt ProMuscle.

All interviews were audio recorded. The interview guides of the interviews are presented in Additional file 2.

Data analysis

Individual interviews conducted during the transitional period and group interviews conducted at the end of the study were analyzed separately. First, all interviews were transcribed verbatim and inductively coded by two researchers (BD, LB, PL) independently to generate codes from the transcripts. Hereafter, one researcher conducted a thematic analysis to organize codes into themes. Themes and underlying codes were discussed with the research group until consensus was reached.

Interviews of the transitional period were analyzed first, to allow that themes derived from these interviews could be further explored during the group interviews at the end of the study.

After all interviews were coded, inductive analysis was conducted to group themes to the trial outcomes adoption, reach, and fidelity.

For this study, a CPD described by Lewis et al. was developed [7, 26]. Based on the results of the group interviews, a causal pathway diagram for each strategy of the ISB was developed to describe possible working mechanisms of the ISB on the adoption, reach, and fidelity of ProMuscle. After the thematic analysis, codes were deductively categorized according to their role in the CPD. For each theme, the research team discussed whether it primarily influenced the activation of an implementation strategy, the working mechanism triggered by that strategy, or the strength or direction of its influence on implementation outcomes. These thematic interpretations were then used as building blocks for the causal pathway diagrams.

Table 1 presents the definitions of terms used within a causal pathway described by Lewis et al. [7]. First, outcome, determinants, strategy, and mechanism were explored. Hereafter, preconditions and moderators at both individual and organizational level were described. After describing individual CPDs for each strategy, one researcher sought overlapping determinants, preconditions, and moderators between strategies. Final consensus was sought on the integrated CPD through discussion between two researchers. Analysis was conducted in Atlas.ti version 24.

Table 1.

Terms and definitions of a causal pathway diagram [7]

Term	Action
Proximal outcome	The product of an implementation strategy that is realized because of its specific mechanism of action, the most immediate, observable outcome in the causal pathway
Distal outcome	Outcome that the implementation processes is ultimately intended to achieve, not the most immediate outcome in the causal pathway
Determinant	Also commonly referred to as “barriers” and “facilitators,” a factor that enables or hinders the implementation strategy from eliciting the desired effect (not included in the CPD)
Mechanism	Process or event through which an implementation strategy operates to affect desired implementation outcomes
Precondition	Factor that is necessary in order for a implementation mechanism to be activated
Moderator	Factor that increases or decreases the level of influence of an implementation strategy
Mediator	Intervening variable that may account for the relationship between the implementation strategy and the implementation outcome

Results

Participants

In total, 25 HCPs were interviewed individually during the transitional period. Of the 25 HCPs, six were lost to follow-up and four were unable to attend one of the three group interviews due to illness, leave, or time constraints. As a result, 15 HCPs participated in the group interviews at the end of the study. Most of the HCPs were female (76%) and more physical therapists (62%) than dieticians participated. The mean age of the HCPs was 40.6 ± 12.5 years.

Causal pathway diagram

The following themes emerged from the thematic analysis: Financing the intervention, Recruitment of recipients, Sustainment of ProMuscle, Insight into context, Implementation experiences, Connection to national policy developments, (research participation), ISB experiences, and Delivery of ProMuscle. The themes were first linked to implementation outcomes and subsequently coded according to their role in the CPD to serve as building blocks of the causal pathway diagram.

For example, recruitment of recipients emerged as a theme from the group interviews and was linked to the implementation outcomes reach, effectiveness, and sustainment. The strategies “align recruitment and intervention with recipients’ needs,” “building external collaborations,” and “educational materials” addressed these outcomes. Based on the interviews, factors such as beliefs about the intervention, having a network, and facilitation in time and money were identified to moderate the influence of the strategies on reach, effectiveness and sustainment of ProMuscle.

The CPD presented in Fig. 3 visualizes the implementation process and describes the mechanism of impact, moderating factors, and preconditions that influenced the impact of the ISB on the implementation outcomes categorized by the RE-AIM framework.

Fig. 3.

Causal pathway diagram of the implementation strategy bundle. Bold factors are moderators identified for 3 or more strategies

This diagram illustrates that four out of the six strategies targeted adoption of ProMuscle, two targeted sustainment, one targeted fidelity, one targeted effectiveness, and two targeted reach. The individual strategies showed overlapping moderators across strategies and the implementation outcomes. Examples of these overlapping moderators include knowledge, collaboration, receiving support, and facilitation, most of these moderators operated at the organizational level.

Lastly, the process evaluation identified preconditions for the mechanism as well as for the proximal outcome for some strategies. These conditions included time, motivation, commitment, and feeling the urge to implement.

The influencing preconditions and moderating factors of the ISB per implementation outcome are presented below.

Adoption

Initial motivation was a key precondition for adoption but was difficult to sustain over time. HCPs reported diverse reasons for adopting ProMuscle, including intrinsic interest in the intervention, opportunities to expand services or collaborations, and encouragement from colleagues. However, adoption scores declined during the trial. When implementation progress lagged behind expectations, motivation diminished accordingly.

In the last few months, I’ve hardly spent any time on it anymore … it demotivated me so much that nothing came of it.

(Physical therapist)

Networking emerged as a moderating factor for multiple implementation strategies influencing the adoption of ProMuscle. Most of the HCPs partnered with a dietician or physical therapist within their municipality to deliver ProMuscle. HCPs indicated that the implementation facilitated a constructive collaboration with the dietician or physical therapist and provided mutual understanding of each other’s qualities. A physical therapist stated that “before, contact was more incidental” and the ISB resulted in “more structured meetings”.

In cases where physical therapists and dieticians both participated in the implementation study, the physical therapist typically took the role as champion and conducted most implementation activities. In addition, support during the implementation from the ISB and from other professionals positively influenced the ISB on the adoption, particularly in the beginning, by having an overview of steps that needed to be taken.

It’s exactly the place where you can find guidance. And in the beginning, I really struggled with that, thinking: Where should I start? What should I do? And fortunately, we had that conversation, which helped me clearly organize things for myself: okay, this is how I’m going to approach it, this is what I need to figure out, and this is where I’ll start. But I think if this had been available, I could have searched for my own questions in a much more targeted way. [physical therapist]

The lack of financial compensation and limited organizational support were identified as barriers by HCPs. Time functioned both as a precondition and a moderator. Not all HCPs were facilitated by the organization, therefore most of the HCPs conducted activities in their own time. However, implementing ProMuscle required more time than anticipated. Lack of facilitation by their organization resulted in the inability to execute all activities or in a slower pace. Which ultimately resulted in declined motivation.

Those side activities just take a lot of time before you can start such a group. And if you don’t get paid for that time … but then you get fed up with it pretty quickly. [physical therapist]

Financing posed a major challenge for adoption. As ProMuscle was not reimbursed, participants paid approximately €250 for three months. HCPs were responsible for setting participation fees and reported struggling to find a balance between affordability for older adults and financial viability for their practice. As a result, many HCPs spent substantial time exploring pricing and assessing funding.

And actually, we also work at cost price; as a practice, you don’t really get rich from it indeed. So, it’s really more of an investment in your target group rather than something you can make a lot of profit from yourself. [physical therapist]

Most of the HCPs explored municipal funding possibilities, of which not all were successful. Having a constructive collaboration turned out to be very valuable for securing funding possibilities. For example, HCPs who retrieved funding were already involved in the municipality or invested a substantial amount of time in advocacy.

And I found it quite difficult, especially because of the municipality and the financing. You’re pitching everywhere, and in the end, if you do some searching, you eventually find some possibilities through connections. [physical therapist]

Decision-making authority functioned both as a facilitator and a barrier for the moderators support and facilitation on the adoption. HCPs with greater autonomy were able to make decisions in their organization more quickly and could execute implementation activities more easily, mostly drawing from experiences and networks. Conversely, HCPs with decision-making authority were mostly senior staff or practice owners/managers, who reported that they lacked time to fully focus on the implementation because of competing responsibilities. HCPs without decision-making authority experienced delays due to dependency on organizational approval.

Interviewer: That it can work, yes. Are there other factors within your own organization or in this neighborhood that you think could influence the implementation?

Physical therapist: My own role, indeed, as I just mentioned, as a practice manager. For example, if I am personally very busy—right now it’s very busy in physiotherapy—so that could influence it. We have a waiting list, and I might prioritize clearing that list over starting a group like this. But I believe, you know, we work together, so if I’ve committed to it, then I just have to do it.

Overall, successful adoption required high levels of persistence and commitment. HCPs emphasized that sustained adoption of ProMuscle in community care settings depended on structured interprofessional collaboration and active organizational facilitation in terms of time and resources.

The time it takes is definitely worth it, but you have to keep persevering. [physical therapist]

Reach

Reach was intended to be affected by two strategies of the ISB; “align recruitment and intervention with recipient’s needs” and “educational material and meetings.” The process evaluation revealed that recruitment rates of older adults willing to participate in ProMuscle were lower than HCPs expected. HCPs reported that the target group was hard to reach, especially (pre)frail older adults.

Convincing older adults to participate in ProMuscle emerged as a moderating factor. HCPs reported that this target group is often unfamiliar in community care practices, and reluctant and scared to intensify their training.

Despite using a wide range of recruitment activities, including newspaper articles, flyers, social media posts, word-of-mouth advertising, and promotion at community events, participants were predominantly relatively healthy and motivated older adults who were willing and able to invest in preventive health interventions. According to HCPs, newspaper articles and personal recommendations were perceived as most effective recruitment methods. Additionally, HCPs attempts to leverage existing (or newly developed) collaborations with general practitioners, local sports coaches, and community centers to recruit older adults yielded limited results.

Facilitation by way of financial compensation of recipients emerged as a moderating factor that influenced the ISB’ impact on reach. According to the HCPs, the cost of the intervention emerged as a barrier for older adults to participate in ProMuscle. The absence of a financial incentive for recipients made some HCPs reluctant to start the recruitment. The lack of financial compensation also influenced HCPs motivation to execute recruitment strategies, which was identified as a precondition for the activation of the mechanism “knowledge facilitation”.

Well, we have a number of vulnerable elderly people who already exercise here, so I mainly tried to approach them to have a personal conversation, like a personal offer. And the response was usually either about finances or something like, ‘Well, I’m taking it easy for now. I need to be careful. Oh, on that leg press, no, I’m not going to do that; it will make things worse for me.’ And we didn’t succeed at all; we even tried together as colleagues to convince those people. [physical therapist]

Understanding of contexts and collaboration with other professionals yielded because of the ISB, which was evaluated as very valuable. Collaboration was identified as a moderating factor for both strategies of the ISB affecting reach. However, according to HCPs, developing collaborations was a time-consuming process. Even before the mechanism of “knowledge facilitation” could be activated, HCPs should have sufficient knowledge and be able to convince others. These factors moderated the influence of the ISB on reach. Not all HCPs were successful in convincing other professionals to collaborate or to refer older adults to ProMuscle. Particularly building a collaboration with policymakers of local government (municipality) was challenging.

But in the end, you get to know your network through that, and that’s really useful. Because it ultimately provides you with good contacts with other sports providers here in [city in the Netherlands]. [physical therapist]

Low referral rates among general practitioners (GPs) and other professionals were reported during the trial. Although most HCPs had a collaboration with the GP, they reported that GPs were reluctant to refer people to the program. HCPs mentioned various reasons; GPs lacked sufficient time, were skeptical about the intervention because it is not reimbursed, preferred other reimbursed interventions, or simply forgot to refer. HCPs noted that GPs or practice nurses, who are already involved with frail older adults, could play a role in the recruitment. HCPs believe that (pre)frail older adults hold the GP in high regard and would be more likely to follow the advice of the GP regarding the ProMuscle intervention.,

HCPs suggested that regular reminders to GPs and other colleagues could help increase referral rates. Also, they believe integrating the intervention into the community care system could raise awareness of more GPs, other professionals, and older adults.

It’s true that it’s not really that very vulnerable target group that you might actually … I also don’t think it’s necessarily people with severe sarcopenia who are participating right now. But perhaps, as it becomes more well-known, other people might be more likely to join as well. [dietician]

Fidelity of ProMuscle

Overall fidelity to the core components of ProMuscle was high. All HCPs reported that the provided materials were clear and sufficient to deliver the intervention in accordance with the ProMuscle guideline. The materials contributed to increased knowledge about nutrition and exercise, which improved HCPs’ confidence to transfer the knowledge and results to professionals and recipients. This contributed to the quality and fidelity of ProMuscle.

Good results among recipients increased HCPs’ motivation to deliver and sustain the intervention. HCPs stated that once older adults started with the program, older adults became more motivated and enthusiastic about the program and adhered to the program. Reasons HCPs gave were the quick results in muscle health and financial investments required to participate.

You can see it in the results. That’s why I think this is such a great program, because you really get results. People show up because they’ve paid a lot for it, which is also great. [physical therapist]

Compatibility with existing work routines facilitated the fidelity of ProMuscle, especially among physical therapists. However, HCPs needed some time to figure out the best way to organize and offer ProMuscle. Time was therefore identified as a moderating factor of the ISB on the fidelity of ProMuscle. Physical therapists reported only minor adaptations to ProMuscle, such as the timing of the intake or alternation of using fitness equipment with exercise using one’s own body weight or dumbbells.

Dieticians reported no adaptations to the consultations during the first 12 weeks. However, most of the dieticians did not offer the group meetings in the second 12 weeks. These ProMuscle workshops aim to help recipients to apply the new knowledge about protein intake into their daily lives by cooking together. Barriers to delivering these workshops were the lack of appropriate location and materials. For the nutritional workshops in the second 12 weeks, implementation climate and facilitation were factors that moderated the influence of the ISB on the fidelity of ProMuscle.

Overall, the core elements of ProMuscle were maintained during the trial. HCPs suggested that handing out printed material, such as information on the importance of nutrition and exercise, examples of exercises and recipes, progress tracking schemes, and an information meeting before the start of ProMuscle could be ways to improve support and adherence.

Barriers and facilitators for the use of the ISB

During the process evaluation, HCPs shared their overall experiences with the implementation of ProMuscle and reflected on the barriers and facilitators they encountered during the implementation and use of the ISB. These experiences transcend the separate implementation outcomes. HCPs indicated that the ISB provided guidance and stimulated most HCPs to remain actively engaged in the implementation. However, tracking activity from the toolbox in which the ISB was presented revealed a low fidelity of the ISB. The ISB was used for a total of only 1635 seconds. The use of the ISB increased between T6 and T7 from 30% to 47% at the end of the study. In total, 39% of the HCPs accessed the ISB during the implementation trial.

Low ISB fidelity was attributed to the fact that HCPs did not always use the ISB as a step-by-step support because HCPs had already started the implementation, did not have time for it, or felt they did not need it. Some HCPs mentioned that the goal of the ISB was unclear, HCPs experienced issues accessing the ISB, it was not clear what they had to do, or they found the ISB too extensive.

Timing of the ISB seemed to influence the ISB’s fidelity. Some HCPs reported that they received the ISB too late in the implementation process. For example, HCPs had already started the implementation and did not know that they still could use the ISB for further support or felt they did not need it anymore. Even for some HCPs, the motivation had already declined due to unsuccessful implementation in the previous weeks. Further exploration of the ISB usage revealed that the HCPs that did not actively use the ISB conducted similar activities as described in the ISB to implement ProMuscle.

The opinions about the ISB were mixed among the HCPs. Some HCPs stated that the ISB was clear, easy to use, and appropriate, gave an overview of the process and what HCPs needed, and the ISBs’ activities were very practical. For example, the ISB resulted in better understanding of the position of their practice within implementation and provided tools to increase recruitment and collaboration.

Yes, that are more activities … Yes, I find it quite useful. It’s just that my motivation was already gone, or at least less, so … But otherwise, I think it fits very well. [physical therapist]

Overall, multiple factors influenced the implementation. Insufficient time, lack of funding, insufficient organizational facilitation, and high intervention costs negatively influenced the implementation and contributed in low recruitment rates. Moreover, moderating factors at a broader system-level, such as embedding ProMuscle in policy, structural financing, and increasing awareness, could not be fully addressed with the ISB, according to the HCPs. HCPs highlighted the need for more support from government, policy, and the intervention developers to address these barriers.

Interviewer: Yes, exactly. But at least focus more on the policy level rather than on the practices.

Dietician: Yes, I think so. Because I believe that every physiotherapy and dietician practice have that target group. And I’m sure they are all willing to do something about it, as long as they know there are opportunities available. And preferably if it is also financially supported. That really makes it a lot easier to recruit people.

Discussion

This process evaluation aimed to explore the working mechanism of an ISB on the adoption, reach, and fidelity of the EBI ProMuscle in multiple community care settings by describing a causal pathway diagram (CPD). Moreover, the barriers and facilitators for the use of the ISB by HCPs were identified. To our knowledge, this is the first study that explored the context and influence of contextual factors to deepen understanding in what, how, and why an implementation strategy works with respect to the EBI ProMuscle [27] through a process evaluation. By focusing on mechanisms and contextual moderators rather than effectiveness alone, this study provides insights that may be transferable to similar community-based lifestyle interventions.

Several organizational and individual moderating factors were identified. Factors at individual-level, including network, convincing others, and knowledge and beliefs about the intervention moderated the influence of most strategies of the ISB. Organizational level factors, such as support, facilitation and collaboration moderate most strategies of the ISB. Additionally, motivation, commitment and time of HCPs were identified as preconditions for most of the strategies to enable the working mechanisms.

Most strategies (4 out of 6) targeted adoption. Knowledge of HCPs and organizational facilitation were factors that moderated the influence of all strategies of the ISB targeting adoption. These findings suggest that factors on individual as well as on organizational level affect the adoption of ProMuscle. This is in line with other studies investigating factors that influence the adoption of EBIs in community care settings [28–30]. To be able to adopt and implement EBIs like ProMuscle HCPs should be facilitated by their organization to deploy implementation activities, gain knowledge, and retrieve resources. Subsequently, facilitating HCPs could indirectly increase motivation.

As highlighted by Michie et al. [31], motivation is highly important in change projects and reflects on intrinsic and extrinsic decisions to change. In our study, for example, for some HCPs the motivation to execute a strategy was negatively influenced by the lack of support (facilitation), while for some, beliefs about the intervention (knowledge) was enough to invest their own time into the strategy. In our study, the execution of strategies depended on the motivation of HCPs. Therefore, motivation was determined as a pre-condition for the activation of the strategies “develop internal networks”, “champions”, and “educational materials and meetings”.

Two strategies of the ISB, i.e. “educational materials and meetings” and “align recruitment and intervention with recipient’s needs,” targeted the reach of ProMuscle. In the effectiveness trial, recruitment rates were low, and no statistical analysis could be performed. To increase the recruitment rates and increase the benefits of the intervention, effective recruitment strategies should be deployed. In the IRLM, which was described prior during the ISB development phase, HCPs and researchers hypothesized that aligning recruitment strategies to patients’ needs and benefits would influence the reach of the target group. However, results of this study showed that HCPs had probably more difficulty in aligning the recruitment strategies than expected beforehand. In contrast to the results in the pilot study, where HCPs expressed they were better able to inform older adults and stakeholders about the benefits of the intervention, insufficient competencies to transfer knowledge moderated the influence of the strategies “align recruitment and intervention with recipient’s needs” and “educational materials and meetings” targeting reach. Moreover, HCPs, and ultimately older adults, need to be convinced of the intervention’s value. Therefore, HCPs should be educated and facilitated to increase knowledge and transfer knowledge about the benefits of lifestyle interventions like ProMuscle.

Additionally, collaboration, the availability of materials and facilitation were other moderating factors identified in this study. A way of facilitation, according to HCPs, is funding of the intervention. Based on the review of Dopp et al. [32], the ISB consisted of the strategy assess funding possibilities. We hypothesized that receiving funding would increase the acceptability and use of the intervention. However, the lack of funding was a greater barrier than expected, due to the difficulty of accessing funding. The need for structural funding was addressed by HCPs during the process evaluation and in literature. When structural funding is available, older adults may be more motivated to participate in ProMuscle, potentially leading to increased recruitment rates. The influence of the strategy “assess funding possibility” on adoption was moderated by the organizational factor collaboration, indicating that having constructive collaborations is beneficial for retrieving funding and facilitating the adoption as well as the reach of ProMuscle. The importance of having a collaboration for successful implementation is highlighted in multiple studies [13, 33]. A successful initiative in the Netherlands is fall prevention. Since 2021 the lobby succeeded in embedding fall prevention in national policy goals and structural funding. Which resulted in an exponential increase in adoption among HCPs and proportion of older adults participating in fall prevention interventions. In this study, it was seen that HCPs that had a collaboration with possible funders or spent much time building a collaboration had more success in receiving funding. Based on the IRLM we could hypothesize that having sufficient competencies to build a collaboration with possible funders fluctuated among HCPs, resulting in insufficient knowledge about the funding possibilities. Moreover, it should be considered that building and maintaining a coalition is very time-consuming and can be hindered by a high workload, absence of a coordinator, and lack of financial compensation (i.e. organizational support) [33].

The low fidelity of the ISB most likely contributed to the non-significant effect on the adoption [34–36]. During the process evaluation, HCPs discussed the ISB and its low fidelity. A previous pilot study revealed that the ISB was helpful and insightful [25]. However, not all HCPs used the ISB actively during the trial. Despite the built-in transitional period to become familiar with the ISB [37], including the provided information about the ISB, HCPs stated they were unaware of the ISB’s aim and potential contribution. During the group interview at the end of the study, HCPs emphasized they would have used the ISB more if they had been better informed about its function, content, and how to use it within the online webtool. This highlights the need for education and support about the ISB and application [8].

Additionally, the timing of the ISB was not convenient for HCPs. By the time HCPs received the ISB, many HCPs felt that they no longer needed it. This reflects a common challenge in stepped-wedge trials, where delayed access to the intervention can reduce its perceived relevance [37]. Before receiving the ISB, most HCPs already conducted activities they deemed necessary before they could start the implementation. Therefore, to be able to create impact with the ISB, the timing of delivery of the ISB should be considered. Furthermore, researchers should be cautious about using a stepped-wedge design because of the delayed timing of receiving the strategy as an intervention.

This process evaluation revealed that many of the moderating factors operate at organizational as well as policy level. According to HCPs, these factors (e.g. facilitation, support, collaboration) significantly influenced the ISB’s impact on the adoption, reach, and fidelity of ProMuscle. This aligns with implementation and health policy research showing that evidence alone is insufficient for scale-up without alignment with policy priorities, funding streams, and governance structures. For example, a similar trend was presented regarding the implementation of a fall prevention intervention. Van der Velde et al. described the influence of contextual factors, such as available resources and financial incentives [38]. The scale of implementation of ProMuscle could have amplified the influence of these contextual factors. Namely, it is known that when implementing at large scale, the so-called system-level factors (i.e., contextual factors at macro level) can be amplified [39], which are often dependent on policy or organizational decisions to adopt and upscale new interventions.

The decision to upscale interventions is mostly policy-driven and influenced by other contextual information or policy influences rather than by research evidence alone [40]. This reflects the system-level barriers this study identified. The results of this study could be used to inform implementation projects with similar lifestyle interventions like ProMuscle. Attention to the system-level factors in an early stage of implementation is therefore necessary. The main hurdle is the dissemination of EBIs like ProMuscle to policy. As highlighted by HCPs during the process evaluation, most of the factors, such as lack of time, dependency on local policy (financing), and lack of awareness among stakeholders and older adults about the benefits of interventions like ProMuscle, rely on the embedding of EBIs in policy to ensure successful implementation, upscaling, and sustainment.

Implications

The results of this are likely applicable to other contexts or EBIs for community-dwelling older adults. When planning for the implementation of lifestyle interventions, implementers should consider strategies on system-level factors. Therefore, support and facilitation from the organizations and relevant stakeholders like policymakers are necessary [6].

Further implementation efforts should consider adapting communication strategies (i.e. evidence should be brief and concise [41], provide cost-effectiveness analysis [40, 41], and include summaries for policy recommendations [42, 43]) to address the research-to-policy gap. Moreover, evidence must be available at the time the decisions are made [40–43], and be delivered by someone they know or trust [41, 42]. Lastly, as highlighted by different studies, policymakers, researchers, and professionals have different needs, and therefore active involvement and collaboration with internal and external stakeholders are essential for successful implementation and sustainment of EBIs in community care settings [40, 44]. Overall, embedding EBIs like ProMuscle into policy requires collaboration built on mutual trust between researchers, HCPs, and policymakers.

The findings of this study highlight the complexity of deploying implementation strategies and the multiple factors influencing the working mechanism and strategies on implementation outcomes. From a researcher’s perspective, it is important to ensure a timely delivery of the ISB, provide education to HCPs on its use during implementation, as well as investigate policymakers’ needs and facilitate collaborations to bridge the research-policy gap and enhance successful and sustained implementation of EBIs in community-care settings. Overall, HCP must be facilitated in time and resources from both their organization and policy to implement lifestyle interventions like ProMuscle.

Further research is needed to investigate the role and possible working mechanism of strategies that specifically address organizational and system-level determinants, such as insufficient organizational facilitation, lack of funding, and limited constructive collaborations.

Strengths and limitations

This study has several strengths. First, by separating the trial and the process evaluation, we were able to gain a detailed and comprehensive understanding of the implementation process. This process evaluation was guided by a widely used framework for process evaluations, the MRC guidance [20]. Second, conducting interviews at multiple time points allowed us to reflect on the entire implementation process [18, 20, 45, 46]. Third, the strategies of the ISB were based on existing literature and co-designed with professionals, enabling the description of a logic model and exploration of possible working mechanisms of these strategies through a CPD. Based on this CPD, moderators that influence the level of impact of the strategies on implementation outcomes could be specified.

This study demonstrates that describing a causal pathway diagram of an ISB is a valuable method for gaining insight into the results of a stepped-wedge implementation effectiveness trial, particularly when non-significant differences could be detected. Moreover, describing a CPD to explore strategies’ mechanisms and identifying factors that moderated the influence of implementation strategies on outcomes contributed to a further understanding of what, how, and why strategies work, a need that has been frequently addressed in implementation science.

This study also has some limitations. During this study we did not explicitly ask about the working mechanism of the individual strategies during the interviews. Because the strategies were delivered as an ISB, it was not always clear to HCPs which strategy they deployed for what barrier. Additionally, due to the low fidelity of the ISB, the effectiveness of the ISB on adoption could not be fully explored. Moreover, due to the complexity and variability of settings, findings of this study must be generalized with caution to other settings. Nevertheless, the process evaluation provided valuable insights into the implementation process and moderators of the strategies’ influences. Many of the identified factors in this study may be similar to other contexts. Furthermore, understanding of how a strategy works creates an opportunity for generalizing results in other contexts, which is increasingly emphasized in implementation science [27].

Conclusion

This process evaluation revealed that multiple factors moderated the influence of an ISB on the adoption, reach, and fidelity of an evidence-based lifestyle intervention for community-dwelling older adults in multiple community care settings. The low fidelity of the ISB probably contributed to the non-significant effect of the ISB on the adoption. While the ISB was perceived as helpful, its impact depends on timely delivery and adequate education on its use. These factors are examples of both organizational- and individual-level factors that influence the working mechanism of implementation strategies targeting adoption among HCPs. However, particularly organizational factors, such as facilitation and support from both the organization and policy, should be addressed to enhance successful implementation, sustainment, and scale-up of the lifestyle intervention ProMuscle. Furthermore, to activate the working mechanism of the strategies, preconditions such as time, motivation, and commitment should be considered when planning for future implementation studies.

Electronic supplementary material

Below is the link to the electronic supplementary material.

Abbreviations

ISB

Implementation strategy bundle

HCP

Healthcare professional

EBI

Evidence based intervention

CPD

Causal Pathway Diagram

Author contributions

B.D and PL set up the study under supervision of DB. P.L. was the contact person for the participating professionals. P.L., LB. collected, coded and analyzed data from surveys. P.L. wrote the manuscript. B.D., D.B., C.V., L.S., L.B. provided feedback and input for the analysis of the data, critically read, and provided feedback for the manuscript. All authors have read and approved the manuscript for submission.

Funding

The research described in this paper was financially supported by a grant from the Regiodeal Foodvalley (162135).

Data availability

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

All participants gave written consent for participation in this trial. The Medical Ethical committee of the University Medical Center Utrecht approved this study (22/050).

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.