1. Treadmill Exercise
CR programs based on either supervised treadmill exercise or home-based walking exercise improve walking ability in PAD patients. A total of 3 randomized trials in which a number of 493 patients diagnosed with PAD were included, demonstrated that home-based walking exercise programs combined with behavioral change techniques improves the 6-min walk test performance more than supervised treadmill exercise interventions (45–54 m vs. 33–35 m) as well as walking ability
[1][2].
In 1995, Gardner et al. performed a meta-analysis of 21 studies on PAD patients and concluded that supervised treadmill walking improved maximum treadmill walking distance from 125.9 ± 57.3 m to 351.2 ± 188.7 m (
p < 0.001, increase by 179%) and pain-free treadmill walking distance from 325.8 ± 148.1 m to 723.3 ± 591.5 m (
p < 0.001, increase by 122%)
[3]. They also identified that increases in the distances to onset and to maximal claudication pain during treadmill exercise are independently related to three essential parts of a CR program which can be considered predictors of the changes in claudication pain distances: claudication pain end point used during the exercise training program, the length of the program and the type of exercise. Based on the results from the meta-regression analysis, Gardner et al. concluded that the most effective exercise programs for patients with PAD include 3 sessions per week, 30 min each, at intensity close to the point of maximum or near-maximum pain onset during exercise for at least 6 months
[2][4].
Later, in 2012, Fakhry et al. summarized in a meta-analysis the results of 25 randomized clinical trials of supervised walking CR programs in which 1054 symptomatic PAD patients were included. Improvements in both maximal walking distance and pain-free walking distance were achieved in supervised walking exercise group (increase of 180 m, 95% CI, 130–230 m and 128 m, 95% CI, 92–165 m), compared to the control group without exercise. A total of 60% of the trials had a total duration between 12 and 26 weeks. In a subgroup analysis based on the length of the programs (<12 weeks, 12–26 weeks and >26 weeks), using multivariate meta-regression, Fakhry et al. observed the tendency to greater mean improvement in maximum walking distance and pain free walking distance in programs with a duration of 12–26 weeks, that those shorter or longer duration, suggesting a maximum benefit for PAD patients enrolled in CR programs with a duration between 12 and 26 weeks, with 3 sessions per week and 30 min of walking in each session
[3][5]. The meta-analysis demonstrated significant functional benefits in treadmill walking performance in patients with PAD after finalizing the supervised CR program, with the reported results suggesting a lower final effect than the one obtained in the meta-analysis reported by Gardner et al. since it included only randomized trials
[6][2].
1.1. Intensity
It is unclear if walking up to the maximal ischemic pain or rather just up to pain’s onset is more beneficial for the PAD patients, moreover since available trials did not show any difference between these strategies
[7].
1.2. Program Length
Fakhry et al. reported significant increases in both pain-free treadmill walking time and maximum treadmill walking time regardless of CR program length (short: 4–11 weeks, medium: 12–26 weeks and long: more than 26 weeks). After 4 weeks of exercise the initial benefit is observed while the maximum benefit of the treadmill walking is achieved after 8–12 weeks of CR. The parameters associated with the 6-min walk test gradually improve due to the fact that the treadmill exercise trains the patient to measure the treadmill walking result (
Figure 1)
[2].
Figure 1.
Key elements of an exercise training program.
2. Home-Based Walking Exercise
Home-based exercise, including behavioral changes, represents an acceptable and affordable alternative to supervised weekly exercise, as it saves time and effort associated to traveling to a dedicated medical center. Home-based walking exercises are more accessible and easier to accept for PAD patients. Regardless of the presence or absence of symptoms, they improve both treadmill walking performance and walk distance in the 6MWT
[2][4][8][9]. Furthermore, the benefits of home-based walking sessions in improving both walking capacity and the 6MWT parameters, compared to supervised treadmill exercise programs, have been proved since 2011 through several randomized trials.
Gardner et al. enrolled 119 men and women with symptomatic PAD to 1 of 3 groups (supervised treadmill exercise, home-based walking exercise, or a control group) for a total duration of 12 weeks. Patients randomly assigned to the home exercise group were instructed to perform exercise or walking sessions of at least 45 min, 3 times a week, at their own pace. At the 12-week follow-up, both patients from the home exercise group and the supervised exercise group showed a remarkable improvement in walking distance without the occurrence of IC and an increasing of the maximum exercise duration compared to the control group. Adherence to exercise programs was similar in the 2 groups (
p > 0.05). PAD patients from the first group walked longer in each session (
p < 0.001), but with a slower cadence than those in the second group (
p < 0.05), resulting in a similar total exercise volume, expressed as MET-minutes (
p > 0.05). No statistically significant differences were identified between the two groups in terms of treadmill walking ability or perimeter walking without IC. It is noteworthy that the study had an overall dropout rate of 23% in the home exercise group and 28% in the supervised treadmill exercise group, pointing difficulties in terms of adherence for PAD patients especially during COVID-19 pandemic
[2][4][8][9][10][11].
In the second randomized trial, Gardner et al. randomized 180 PAD patients with IC to 3 groups: supervised treadmill exercise, home-based walking exercise and a light resistance training group. At the 12-week follow-up, patients from the first group had significantly greater improvement in treadmill walking compared to home-based exercise (192 ± 190 s vs. 110 ± 193 s vs. 22 ± 159 s) and in the time to onset of claudication pain on the treadmill (+170 s vs. +104 s vs. +17 s). Beneficial effects were also observed in the 6-minute walking distance which improved by 45 m in the home-based walking group compared to 15 m in the supervised treadmill group and 4 m in the control one
[5][10].
The Group Oriented Arterial Leg Study (GOALS) is the only randomized clinical trial of home-based exercise for PAD patients both with and without IC. A total of 192 participants were randomized to a Group Mediated Cognitive Behavioral (GMCB) intervention group or to a control group. The GMCB intervention methods included social cognitive behavioral change theory and group support in order to increase adherence to home-based walking exercise programs and therefore increasing the walking performance. The intervention group had weekly meetings at the medical center with other PAD patients and a facilitator. At the 6 months follow-up, the intervention group had a significantly improved 6-minute walk performance compared to the control group (+42.4 m vs. 11.1 m). Improvements were also observed in the case of pain-free treadmill walking time (+1.01 min compared to the control group) and in maximum treadmill walking time. Support sessions were discontinued after the first 6 months, but the benefits on functional status persisted at the 12-month follow-up
[9][12][13].
CR programs for PAD patients should be permanently adapted to the associated comorbidities and needs in order to achieve the desired results. The aim is to achieve a total exercise session duration of up to 50 min, with a gradual increase of 5 min each week, starting from a minimum duration of 30 min per session. The PAD patient should walk until close to reaching maximum leg pain. Even so, trials demonstrated that walking until the onset of intermittent claudication is also beneficial. Rest breaks are acceptable for PAD patients, with the recommendation to resume walking exercise as soon as leg pain has subsided
[2][4][8][9][10][11].
Collins et al. also investigated the role of behavioral intervention methods on the adherence of PAD patients to home-based exercise programs. A total of 145 patients with PAD and diabetes were enrolled for 6 months and randomized into 2 groups: a behavioral intervention group vs. an attention control group. The patients from the first group had an individualized counseling session at enrollment, followed by a walking session weekly with an instructor and other patients with PAD at an exercise center and 3 days of walking at home (with a total of 50 min of exercise per session). All patients received bi-weekly phone calls, to evaluate progress in the first group. Compared to the previous study, at the six-month follow-up the investigators found no statistically significant differences in treadmill walking parameters between the two groups
[14][9][15].
The impact of COVID-19 pandemic on home-based CR programs has been assessed by Lamberti et al. in a study in which 83 patients with PAD were enrolled within 9-month before the lockdown. The physical activity consisted of twice a day 8 min sessions of slow and intermittent in-home walking. During lockdown, the patients received regular telephone questionnaires regarding general health, adherence to exercise program and evolution of symptoms. Only 80% of the PAD patients showed up for the follow-up after lockdown. The pain-free walking distance improved improved directly proportional to the time since enlistment before the lockdown (
p < 0.001) regardless of gender and comorbidities. Improvements were also observed regarding body weight, blood pressure and ankle-brachial index
[16].