Table 3 Themes, definitions and illustrative quotes for the nested qualitative analysis

Theme 1. Reasons for participation*

1.3 Sense of duty

This subtheme includes CG participants understanding of the importance of a CG and the commitment they made to the study. They expressed a sense of responsibility.

‘This work might lead to something that gets implemented by the NHS, which could benefit millions of people…So, you know, it would be churlish not to continue with the study’ (RS60, CG when asked on thoughts when found out they were randomised to the CG)

‘Well, I made a commitment. I must admit that I was disappointment to be in the control group, because I wanted to be, you know, more active I wanted to be, you know, more part of, you know the, you know the science involved, but I’d made a commitment to you that I would do it…I’d made a commitment, you know, it’s not very onerous is it?’ (RS23, CG)

‘Well, I mean, I was disappointed because you know, part of my reasons for signing on was to see what it was all about and get it…if you haven’t got a control group, you haven’t got a study. So and you know, this work might lead to something that gets implemented by the NHS’ (RS60, CG)

Theme 2. Study procedures

2.1 Acceptability and trust

This subtheme includes participants’ voices (CG and IG) regarding the acceptability and trust of study procedures.

‘How do you make a diabetic study if you don’t have any impact on the sugar levels?…I think It’s irrelevant. It doesn’t matter. If you don’t, if you don’t know what your sugar levels are’ (RS25, CG, the importance of diabetic specific measurement)

‘Measuring your own waist circumference. I mean, anybody measuring my waist circumference to me is, is always going to be out’ (RS60, CG, challenges with performing own waist circumference measurement)

‘The walking and saying ‘stop’ I never quite understood that one, because I didn’t, I never thought it was that long as length of space’ (RS07, IG, questioning the validity of the 8-foot walk test within the SPPB)

2.2 Feasibility of measures

This subtheme explores the participants perceptions of the feasibility of the measures (CG and IG) i.e., can the study procedures/measures be carried out?

‘I liked having the instruction sheet. So, I knew on the first session what I was going to have to do’ (RS46, CG)

‘Yeah, it’s the plaster bit you know where you you cover it and you stick it on your thigh? Yeah. Somehow. It wasn’t so much of a allergic reaction. Such. Yeah. It. I think I started to itch a little bit’ (RS30, CG)

‘Apart from having to be careful when I was in the shower. I didn’t have an issue with it. You know, and even then the the way that it was connected to my leg or affixed to my leg was quite waterproof so i It wasn’t an issue for me’ (RS04, IG)

‘it’s not very onerous is it? Every couple of months, you know, do a couple of exercises and put a tab [activPAL] on your knee I mean it’s on your leg. It’s not very onerous’ (RS23, CG)

2.3 Hawthorne effect

Participants in the CG, and some in the IG, mentioned changes to their behaviour (sitting and physical activity) in response to measurement and observations i.e. a Hawthorne effect. In addition, there was one example of contamination.

‘Every time I was standing up, either when I was in the garden or doing the washing up, or wherever, going for a walk or whatever, psychologically in my brain, I was thinking, “that’s a good thing,” because this study is all about, you know, measuring, you know, how often you stand up, whatever, you know, cutting [did enough] time that you spend sitting down, so psychologically, I do think that being, having had to chat with you at the start of the, of the, of the course, of the of the study, you know, and when you explained what it was all about, that had an impact on me’ (RS23, CG, Hawthorne effect)

‘A little bit in the sense that, you know, if I’m watching TV, literally, you know, if we’re having an early dinner, and I’ve got to have a time in between. So when I’m sitting down to watch TV, I would, you know, do the steps. Just get up and just march’ (RS30, CG, Hawthorne effect- creating own intervention)

‘Yeah ((overlaps)) So, so I understood, but if I didn’t understand would I have done it? I dunno? But I think Mum was a good reminder because mum was having stuff so that was my kind of- So remember, I’ve got this other reminder going on. ((phone rings)) Sorry, Marsha, now my phone is going on’ (RS09, CG- Potential Contamination-Mother in the RESIT IG)

‘I felt a bit of like, oh for the next one. I want to be speedier, I want to be going to walk more I want to be thinner. (laugh) I was motivated for the first one [measurement]. But when I like I said, I think when I didn’t get any feedback, I just felt- oh well, I’m not going to know so whatever. It’s just, do whatever’ (RS14, IG, Hawthorne effect– motivation to improve measurements)

Contrasting quote‘I don’t remember the measurements. And I didn’t. I didn’t pay attention to it. I felt maybe it’s not as important’ (RS25, CG- contrasting quote on Hawthorne effect)

Theme 3. Delivery and experience of the RESIT intervention

3.1 Planned and unplanned BCTS

This subtheme includes the active ingredients (BCTs) the intervention participants (IG) and HC’s acknowledged. This includes those in the protocol and any additional BCT’s.

‘The only thing I did do if I was watching a program and I knew, I watch a lot of series, and they would normally be about 45 min long. And and I’d know that I’ve watched, before I come to the end, and I said, ‘time to get up and go and have little wander around’. That’s basically all I added to mine, yeah’ (RS63, IG, BCT 1.2 Problem solving)

‘I felt like I had something new to tell her every time a new goal I hit, something that I was doing that I could I could speak to her about? And it was almost pleasing her. (laugh)’ (RS14, IG, BCT 1.1 goal setting (behaviour); BCT 1.5 review behaviour goals)

‘That was the eye opener, I think that was the you know, the little movements that make a difference’ (RS14, IG, BCT 2.2 feedback on behaviour)

‘Yeah, he was very good listener in the beginning, and then he will just um tell me that, okay, instead, why don’t you try this way? And just give it a go and see how it feels, you know? He was always giving me the healthy choice and suggestions’ (RS68, IG, BCT 3.1 social support [unspecified])

‘what, what the RESIT did was to really, really reignite in my mind This this television program about the poisons that build up If you’re not, I won’t say continually active, but if you’re sat down, you shouldn’t be sat down for prolonged periods of time’ (RS42, IG, BCT 5.1 information about health consequences)

‘Cos if you’re wearing a watch, you’re doing the steps, it’s recording your sleep, your heartbeat, etc, etc. And it does tell you you’ve been sitting for too long so you can stand up and you know, walk about for a few minutes, then that’s really helpful. It does occasionally but then it goes quiet for maybe a day or two and doesn’t do anything. Then all of a sudden tell me I’ve been sitting for too long. And I think, ‘whoa, I’ve been sitting for two days’. You’ve got to see the funny part of this as well ((laughs))’ (RS63, IG, BCT 2.3 self-monitoring of behaviour; BCT 7.1 prompts/cues)

‘I think the most obvious one, I guess, is the Stand Up! app. Oh yeah, I think. I wasn’t aware of it as an app as such but I was aware of the need to get up every 45 min for five minutes or what have you. But in having the app and using it has made a difference. And, you know, I got to be honest, there are days when, you know, even though the app tells me to get up you can’t because of work demands, but at least it does allow you to start doing some of those little things easily. So that helps’ (RS22, IG, BCT 7.1 prompts/cues)

‘I did quite quite often emphasize that it doesn’t have to be you don’t have to be doing formal exercise or activity doesn’t have to be a walk, it can just be like taking a break. A lot of the time is taking a break from your desk at work and getting up to go to the loo or getting a coffee or chatting to a colleague things like that. So those are all things to break up their sitting time. So, a lot of them found it kind of challenging at first too, because you’re so used to just sitting down and working away all day. But the more you kind of get these habits built into place, the more they become quite easy to follow up with after time’ (HC1, BCT 15.1 verbal persuasion about capacity)

‘It was like the motivation kick for those during that sessions, you know, give chance to express feelings. how we feel. Yeah, it was good’ (RS47, IG, BCT 3.3 = social support [emotional] - additional BCT not specified in the protocol)

3.2 Intervention fidelity

This subtheme looks at intervention fidelity i.e., was the intervention carried out the way it was intended?

‘So actually, on that note, I think only one participant decided that they only wanted three calls. And they didn’t need the fourth one. So they’re just going through that. So that’s fine. And yeah, I didn’t know. On the coach side. I was like, Do you guys want me to definitely do the fourth those that and be so I think I didn’t do about that. But yeah, we just did three and that was fine’ (HC4)

‘I’m not sure I’ve done any of that have I?’ (RS44, IG when asked about health coaching sessions).

‘Same thing, the fear of technology, I don’t want to learn new, new new technology things. Because the brain is so scarred up with so much new things. And it’s so deep and variety of work. I’m getting involved. And now it feels like over in the brain that I don’t want more information’ (RS47, IG- when asked why they did not engage with the apps)

3.3 Acceptability of the intervention

This subtheme theme includes acceptability of the RESIT intervention components including the online education session, the health coaching sessions, and the apps and wearables. There is a link to the BCTs as these were embedded in all aspects of the RESIT intervention.

Online education session

‘I can’t remember. But if I go on website now, then I can perhaps understand a bit more. But I can’t remember right now’ (RS47, when asked about online education package)

Health coaching

‘So those are all things to break up their sitting time. So a lot of them found it kind of challenging at first too, because you’re so used to just sitting down and working away all day. But the more you kind of get these habits built into place, the more they become quite easy to follow up with after time’ (HC1)

Wearables and apps

‘So the stand up! App, as an example, I’m still using it now. The app’ (RS22, IG)

‘If I was sitting for too long, the reminder was good. But if I had got up, then I thought Oh not sure about this, I don’t know’ (RS11, IG)