Those participants of the original interventional study who completed all former study assessments (n = 29 of 32) were invited to participate in the 1yrFU. The interviews took place between May and June 2022. A total of 17 participants provided answers to the open-ended questions of the conducted semi-structured interviews. When analyzing the transcripts, no additional categories were deductively developed, so the eight main categories developed inductively covered all relevant information and therefore remained as they were. After 14 interviews, data saturation regarding barriers and facilitators was achieved.

Women represented 76.5% of the sample and men 23.5%. Of the 17 participants who participated in the 1yrFU, 4 contracted COVID-19 again, which corresponds to 23.5%.

At the 1yrFU the average age of the sample was 49.9 ± 8.9 years and did not differ between group allocation. The CEG consisted of 7 people (41.2%) and the DEG of 10 participants (58.8%). Detailed information about the characteristics of the participants at the 1yrFU are depicted in Table 1. No significant group differences between CEG and DEG were noticed at the 1yrFU (Table 1).

Table 1 Participant 1‑year follow-up characteristics differentiating between group allocation

Facilitators, including how often a statement related to a specific category was mentioned separately during the interviews are depicted in Table 2 under the term frequency. Improving physical and mental health was named most frequently as a motivating factor for physical activity with 19 mentions. Respondents in this category reported benefiting from sports or exercise both physically and mentally:

“Sport is not only good for me physically, but it is also extremely good for my mental health” (Irene, 53, F, CEG).

Table 2 The 10 most frequently mentioned facilitators and barriers across the entire study population and depending on group allocation CEG and DEG

Sport has high priority was named 18 times. It was described by the participants in this category that performing sport had great importance in their lives and was therefore prioritized over other things.

“Sport is a fixed part of my life” (Elisabeth, 47, F, CEG)

The category (re)build physical and cognitive performance was mentioned 15 times. A measurable or noticeable increase in physical and mental endurance was described by participants as motivating:

“It motivated me to continue, because I realized how successful I had been” (Anja, 50, F, CEG)

Training in the group with 13 mentions was also of high priority regarding motivating factors for physical activity. The participants found it a motivating factor not to pursue a sporting activity alone, but together with other people, as this enabled them to motivate each other.

“Yes, as I said, it’s motivating that there are two of us” (Claudia, 55, F, CEG)

Barriers, including how often a statement related to a specific category was mentioned during the interviews are depicted in Table 2 under the term frequency.

Exhaustion was mentioned 21 times as the primary barrier. This included exhaustion both in terms of post-COVID-19-related symptoms as well as the exhaustion due to numerous day to day responsibilities (job, family).

“When you come home from work exhausted, you don’t have enough energy for a workout, which is demotivating” (Renate, 42, F, CEG).

Sport has little priority (mentioned 17 times). This category included statements that were primarily based on a lack of time resources to engage in sporting activities.

“Yes, (… I try to have time for sports, but only …) depending on how it goes, how it works out in terms of time, with family and work and yes appointments” (Anton, 53, M, CEG)

Procrastination (mentioned 12 times). Participants described that they often lacked the inner will to motivate themselves to exercise.

“I would not have been able to overcome my weaker self” (Alois, 42, M, DEG)

COVID-19 measures and risk of infection (mentioned 8 times). On the one hand, due to the lockdowns COVID-19 severely restricted the range of sports, for example in a fitness center. On the other hand, participants also described the fear of contracting COVID-19 when exercising in a separate room with other people.

“And I also used to have the fitness center before COVID. But then I did not want that during the pandemic” (Ursula, 63, F, DEG).

To gain a more detailed insight into the facilitators and barriers to physical activity, we separated participants who reported continuation of their regular aerobic and resistance exercising from those who discontinued exercising in the past year.

When comparing the two subgroups in terms of facilitators for exercising, we found that participants in the CEG mentioned 14.6 motivational factors per participant, while in the DEG only 7.7 motivational factors were mentioned per participant. When comparing the two subgroups in terms of barriers for exercising, we found that participants in the CEG mentioned 3.9 hindering factors per participant, while in the DEG 6.8 hindering factors were mentioned per participant. The absolute number of facilitator mentions was higher in the CEG compared to the DEG (102 vs. 77). On the other hand, putting the categories in order shows that the top three facilitator categories were similar for each group. While the top three facilitators in the CEG were (re)build physical and cognitive performance, sport has a high priority, and improving physical and mental health, the top three in the DEG were training in the group, improving physical and mental health, and sport has a high priority. This means that two of the top three facilitators were the same in both groups. The groups differentiated with respect to the factors (re)build physical and cognitive performance, which was substantially higher prioritized in the CEG (1.6 mentions/participant vs. 0.4 mentions/participant) and training in a group, which was substantially higher prioritized in the DEG (1 mention/participant vs. 0.4 mentions/participant).

“I knew I had to continue exercising to not get long-COVID again” (Carla, 50, F, CEG).

“So maybe the motivation to be in a group, that you have to or should come regularly or so this group feeling” (…) is beneficial for practicing regularly (Stefanie, 30, F, DEG).

In absolute numbers, barriers were mentioned more often in the DEG compared to the CEG (68 vs. 27); however, the order of the categories revealed that the top three barriers, exhaustion, sport has little priority and procrastination, were not only the same in both groups but also appeared in the same order. Exhaustion, as the primary barrier in both groups, was mentioned twice as often in the DEG than in the CEG group (14 vs. 7 mentions). Participants referred to actual physical exhaustion that prevented them from engaging in physical activity, and which affected participants in the DEG group more often.

“Sometimes nothing worked at all, where I had the feeling that every movement was torture. Pain in the limbs, exhaustion, (…), where everything was an overwhelming effort and nothing worked anymore and the shortness of breath was also stronger again” (Laura, 59, F, DEG).

Furthermore, exhaustion was also mentioned related to the fear of being re-infected with COVID-19. This was mentioned six times in the DEG, while the CEG it was mentioned only twice. Participants in the DEG also mentioned more often than those in the CEG that other priorities prevented them from exercising more often (sport has little priority, 12 mentions in the DEG vs. 5 mentions in the CEG).

“So there’s energy for things like that, I just don’t have the time to juggle it all” (Erwin, 49, M, DEG).

Procrastination was mentioned twice as often in the DEG compared to the CEG (8 vs. 4 mentions).

“These are my inner demons, as they say. They are just very strong with me” (Elvira, 64, F, DEG)

Nevertheless, despite the differences in absolute numbers, the order of the top three barriers were the same in both groups.

The physical performance parameters 30secSTS and 6 MWT showed a visible increase during the exercise intervention phase of the original study ([12]; Fig. 1a, b). The group comparison CEG versus DEG, which gets relevant only after the 8‑week follow-up (8wkFU) of the original study [12], showed a slight increase in the mean 30secSTS performance between the 8wkFU and the 1yrFU for the CEG, while the mean number of repetitions decreased in the DEG at the same time (Fig. 1a); however, inferential tests showed that this difference was not significant (p = 0.29). Similar to the 30secSTS results, the 6 MWT also showed a performance increase between BL and 8wkFU during the original intervention period [12]; however, in the long-term between the 8wkFU and the 1yrFU, both the CEG and the DEG decreased their performance similarly (Fig. 1b). Unsurprisingly, the mean differences between the groups did not differ significantly in the 6 MWT (p = 0.82).

Fig. 1

Development of performance parameters (a 30secSTS and b 6 MWT) over the duration of the whole study including the initial supervised exercise intervention phase. 4wkFU 4-week follow-up, 8wkFU 8-week follow-up, 1yrFU 1-year follow-up, CEG continuous exercise group, DEG discontinuous exercise group, 30secSTS 30s sit-to-stand test, 6 MWT 6-min walk test, reps repetitions

Further quantitative outcome parameters are shown in Table 3. A significant increase in dominant handgrip strength between BL and the 1yrFU (t(6.52) = −2.42, p = 0.049) was shown. (Table 3) Moreover, a significant change in the PCFS between BL and 1yrFU (z = 2.18, p = 0.048) with lower scores in the CEG compared to the DEG was shown (Table 3).

Table 3 Change of outcome parameters over time points (BL, 8wkFU and 1yrFU) between CEG and DEG

Between the 8wkFU and the 1yrFU no significant change was observed in any of the parameters, however, in the body mass index (BMI) there was a trend (t(9.55) = 1.85, p = 0.095) towards lower values in the CEG.

Spearman correlation analysis was calculated to analyze the relationship between performance outcomes and psychological health outcomes. At the 1yrFU, the only psychological health outcome which significantly correlated with a performance parameter at the same time point was anxiety (GAD-7) which showed a significant inverse correlation with the 30secSTS (ρ = −0.57) (Fig. 2).

Fig. 2

Spearman correlation between performance outcomes and psychological health outcomes. BL baseline, FU1 4-week follow up, FU2 8-week follow-up, FU3 1-year follow-up, 30secSTS 30-seconds sit-to-stand test, 6MWT 6-minute walk test, BRS brief resilience scale, GAD-7 generalized anxiety disorder-7, PHQ-9 patient health questionnaire-9, PSS-10-Ges perceived stress scale-10 total score, WAI-K work ability index short form