In line with the upcoming interest in studying potential associations between daily PA and their impact on cardiovascular risk reduction and mortality36-42, this study assesses the effect of SET on proportions of IC patients meeting the ACSM lower and higher limit recommendation for PA and public health. Several studies registered activity levels in IC patients.15,17-21 However, this parameter was never considered as a primary outcome value. McDermott et al. showed in a 7-day measurement model that IC patients significantly improved their PA levels (in activity units) after 6 months of home-based exercise.21 These findings might in part be confirmed by the present results. Although our study was based on a shorter follow up period and based on supervised therapy, SET increased the percentage of IC patients achieving the lower and higher limit of daily PA level as recommended in the international ACSM guideline11. However, firm conclusions cannot be drawn, since some patients did show a decline in PA level and mean values for ambulatory activities (e.g. walking time, total number of steps) were not influenced after a period of SET. Probably large variations in activities per patient (duration as well as intensity) and between patients in combination with our relatively small study population could have caused this contradiction. Therefore further research is necessary to optimize the determination of PA levels in patients suffering from IC. However from our results it may be argued that a 3-month SET program may have beneficial effects on increasing daily PA in an IC population.
It was hypothesized that an increased walking capacity would result in an improved PA level of IC patients. Although both the percentage of patients meeting the ACSM limits and walking capacity significantly improved after 3 months of SET, no significant correlation between the change in PA levels and the increase in walking distance was found. Therefore one may argue that components of a SET program other than an increased walking capacity influence daily PA. Our findings might suggest that solely focusing on improvement of walking capacity has a limited value in optimizing SET treatment efficacy. It appears that patients who are able to walk further (because of a decrease in IC symptoms), will not use this capacity to walk more often, longer or with probably more intensity in daily life.
The effect of SET on QoL is still subject to debate.8 A recently published meta-analysis found a positive trend in improved QoL after three months of SET, although only the SF-36 "general health" role appeared significantly increased.8 In addition, McDermott et al. found no group differences in changes in the SF-12 PCS or MCS subscales.21 In contrast, we found a significant increase in both the physical functioning and the bodily pain role after three months of SET. Although patients showed an increased walking capacity, no significant correlation in the change of SF-36 values was found. This finding was recently confirmed by others reporting that the improvement in self-efficacy, satisfaction with functioning, pain acceptance and social functioning after six months of home-based walking exercise compared to a non-exercising control group was independent of walking performance.43 In combination with our finding that walking capacity might be of diminished value, a shift in SET treatment paradigm seems necessary. Future research should therefore focus on the optimization of SET programs other than increasing walking capacity alone (intrinsic motivation, life-style, patient satisfaction and expectations, social functioning, etc.).
Unfortunately a large number of participants were lost to follow up which may have potentially resulted in a selection bias. However, this is probably not the case as any differences regarding baseline characteristics between the study group and excluded patients were found. Furthermore both study groups were a representative reflection of the general PAD population encountered in a vascular outdoor clinic. An important reason for this substantial loss to follow up is the fact that 56 of the 126 included patients were recruited from a previous performed study.16 Only 23 of these 56 patients were eligible for inclusion, because in the other patients the 3 months follow up period was already expired. Furthermore, introducing the Dynaport MoveMonitor from a research setting to daily practice in our patient outdoor clinic may boost wear compliance, as was observed in comparable research concerning COPD patients.44 Unfortunately, a reliable sub-analysis between revascularization and SET treatment could not be performed as only 16 participants did receive such a treatment. Future research is needed to identify the effect of different IC treatment modalities on daily PA levels and ambulatory activities.