Table 4 Overview of themes and illustrative quotes

Low energy levels were dominant internal barriers to PA engagement

“It’s just because I know it will be tiring” (Jenny, 44)

“Just when I’m feeling unwell, lack of energy. Most days I don’t be in the mood to go to the gym, just through fatigue and tiredness” (Robert, 41)

“Low energy, if I’m not feeling the best, I’d use that as an excuse” (Emily, 50)

“Some days I’m just absolutely wrecked, like I can be so tired. I just don’t want to move, just don’t want to go out, sometimes I don’t even want to sweep the floor in the house, it’s that type of…just comes out of nowhere” (Paul,30)

“Energy wise, yeah, I find my energy levels are even when I wake up in the morning are low” (Keith, 38)

“I have just started college and on the days where I'm in, I know that I don’t have the energy to work out and a full day in college on the same morning” (Dorothy, 29)

Time and the weather were dominant external barriers to PA engagement

“it’s probably like time and weather” (Frank, 26)

“I suppose time is one thing, obviously having CF and working full time and family it’s tough” (Keith, 38)

“Time is definitely one as well” (Hannah, 36)

“I work kind of in the evenings times 3 to 11 at night. So going to the gym I have to be up early to kind of go in and get to the gym early. And I have no problem with doing that, it’s just at times you wake up and you feel so exhausted from work that it’s just too difficult. Whereas if I had a schedule around 9 to 5, I’d go to the gym on the way home I’d do it more often” (Jason, 35)

“The weather is getting bad, so, going to be stuck in doors more, will be hard to get up there, the motivation might slack a bit” (Paul, 30)

“My motivation if the weather is [bad], my motivation is squat” (Jenny, 44)

“As I say that’s weather depending” (Richard, 49)

“The Irish weather I find is a barrier for me to get to be physically active” (Matthew, 28)

“I don’t walk in torrential rain and… the winter months” (Jenny, 44)

Positive past PA experiences were typically associated with more regular PA participation, driven predominantly by enjoyment

“Positive, from the age of about, when I was in school and stuff, and I was always playing sport, I was always playing football” (Robert, 41)

“Positive, I always try to keep active…I have always kind of done it throughout my life” (Emily, 50)

“So, as a kid, I wouldn’t have noticed any difference from anyone else, I don’t think. Very active” (Hannah 36)

“So, if I go for a run first thing in the morning it helps me clear all the mucus and stuff in my lungs. Then the afternoon I go to the gym for an hour weight session. And I do that for 2 days and then I have the third day off. And then I go through all that again.” (Robert, 41)

“I usually try and go to the gym 3 mornings a week and that would include 2 spinning classes and a hit class, high intensity class. So they would each last approximately 30 min each but they would be quite physical.” (Emily, 50)

“Yes, so at the minute I am exercising probably 5 or 6 days a week…I would run on the treadmill for about 10 or 15 min depending on how I'm feeling between 6 to 7.5 miles, that’s like speed wise. So, then I’d do some weights I do the sit ups” (Dorothy, 29)

“I've always really enjoyed the exercise.” (William, 34)

“I do enjoy the physical aspect of it, I enjoy putting my music on and just running the treadmill” (Dorothy, 29)

“it’s fun and it’s enjoyable” (Carol, 36)

Value of exercise-related outcomes: accomplishment and affect regulation

“I enjoy kind of the buzz you get…the way it clears your head…you kind of feel better afterwards” (William, 34)

“I like the buzz you get and the feeling after that you have accomplished being able to physically do an activity, everyone in the room…they don’t know I have mild CF and I kind of look and say, god I am able to keep up with them” (Robert, 41)

“Sometimes it is the best medicine for you, you go off burn some calories, get a sweat on and you do feel the better for it” (Emily, 50)

“I like the benefits of it, the immediate effects of it and the long term effects, just keeping the lungs healthy I have to say that’s my main benefit from it” (John, 31)

“The great feeling you have after doing some activity really that you feel you got loads of energy, you feel like you have actually done something healthy” (Jason, 35)

“Makes you feel good, even if you are stressed out at home or you had a bad day… just relieving that stress you have, even if you are tired and you think ah can’t be bothered… you always feel better after it and you say you are kind of glad [you] went” (Robert, 41);