The present study shows that improvements in physical fitness and muscle function gained by a 3-months PT-X period in elderly patients with permanent AF disappeared after a 3-months’ period without organised exercise. In addition, there was a reduction in HR-OoL. A strategy for conserving improvements after a rehabilitation period is thus essential.

Several studies among patients with cardiovascular diseases other than AF show that patients have difficulty continuing exercise and maintaining a sufficient physical activity level after finishing exercise-based cardiac rehabilitation [22,23,24]. The results of the present study both confirms the importance of developing a strategy for preserving achieved improvements and expands the knowledge of what happens when systematic circulatory training is not continued. Such information might strengthen the motivation for continued training both among patients and health care providers.

The physical fitness improvements following PT-X, 2 mL × kg− 1 × min− 1 measured as maximum work load, were comparable to those achieved in patients with chronic heart failure, in whom such improvements were associated with decreased mortality and hospital admissions during the follow-up period [25].

The period following the end of the PT-X period is compatible with the concept of detraining. Detraining is defined as the cessation or reduction of training, or a decrease in physical fitness caused by training cessation or reduction [26]. In the English literature, we have found no previous report addressing the impact of detraining in patients with permanent AF.

Previous investigations have shown that detraining causes central and peripheral alterations in athletes and recently trained healthy individuals [27,28,29]. These alterations are multifactorial, and include a reduced VO2max due to reduced blood volume and higher heart rate response, which reduce stroke volume and affect cardiac output [29]. The peripheral alterations include reduced muscular capillarisation and oxidative enzyme activities, and a decreased arterial-venous oxygen difference and reduced oxygen delivery to the cells, which affect mitochondrial ATP production [27]. We also observed significant loss of muscular endurance, in line with previously reported results of detraining in patients with and without cardiovascular disease [30,31,32]. Our results corroborates those of Volaklis et al. [31] and Ratel et al. [32], which showed that detraining led to reversal of improvements of VO2peak and muscular strength among patients with cardiovascular disease and in older adults [27, 28, 30,31,32]. Our study showed that detraining had similar effects in patients with permanent AF.

Furthermore, the period of detraining led to an impaired HR-QoL, with decreased scores on all SF-36 dimensions, and consequently a significant decrease both in physical function and mental health as well as in the mental component score. In some dimensions, the post-detraining scores were lower than the scores before PT-X. In three of these dimensions (Role Physical, Vitality, and Social Functioning), the SF-36 scores exhibited a reduction of at least 5 points, which is considered a clinically and socially relevant difference. Notably, the patients showed a 13-points deterioration in the Role Emotional dimension, which is considered a moderate change [21].

These findings indicate that both physical fitness and HR-QoL deteriorate if PT-X-induced improvements are not preserved.

Risom et al. [9] found no evidence that PT-X improved HR-QoL. This was also our finding in the first part of our study, in which the patients self-rated scores were similar to in the normative Swedish population of the same age range [10, 33]. Teixeira-Salmela et al. reported that HR-QoL increased with exercise training in the older population, and this increase persisted during detraining [30]. They proposed that patients felt better about their physical abilities and, therefore, adopted a more active lifestyle. That situation differs from the situation in our study, in which patients were asked to avoid organised exercise. Clearly, adherence to these instructions led to a reduction of HR-QoL. Our results are in line with the findings of an observational study, in which older individuals (> 65 years of age) participated in a detraining period after a period of organised exercise [34]. The participants received instructions similar to those given in the present study, and the results showed significant deterioration of all dimensions of the HR-QoL as measured by SF-36, as in our study [34]. These findings clearly confirm that after cessation of PT-X, it is crucial to support patients to maintain their physical fitness and HR-QoL.

In this study, we investigated the consequences of not pursuing training after a period of PT-X in patients with permanent AF. Due to the high evidence of benefit from improved physical fitness this may seem ethically questionable. It is, however, well known that it is difficult to maintain good exercise habits, and the need for support in lifestyle changes is an important issue. Such a strategy also requires resources and needs to be supported by scientific evidence, which was scarce when this study was initiated in 2013. The results of the present study corroborates the need to continue exercising after a period of successful PT-X, and can thus serve to motivate patients to pursue this goal and health care authorities to allocate suitable resources.