Table 1 Summary of self-report primary and secondary outcomes, process, and screening variables, and respective assessment measures

 MWD

 PFWD

 FWD

Treadmill test (TT)

The treadmill test is an accepted method used in patients with IC to evaluate walking ability [34]. Performing a treadmill test before and after an intervention can provide an objective assessment of change in performance [35]. The modified Gardner-Skinner Treadmill Protocol will be used, where participants will begin to walk on the treadmill at 1 km/h with a 0% grade. After 2 min, the speed is increased to 1.6 km/h, at 0% grade. Then, the speed is increased by 0.8 km/h every 2 min until reaching 3.2 km/h. After reaching 3.2 km/h, the speed is kept constant, and the grade is increased by 2% every 2 min. The main difference between the modified protocol used and the original Gardner-Skinner Treadmill Protocol [36] is that the protocol used is better adapted to this study sample capabilities and equipment, since the original Gardner-Skinner Treadmill Protocol has a continuous speed of 3.2 km/h, and the grade is increased by 2% every 2 min. During the exercise, blood pressure and heart rate will be continuously monitored (Domyus Incline Rune, China). To implement the treadmill protocol, patients must be at rest, informed about the termination criteria (excluding safety criteria), about permission to use the handrail support, and informed about the claudication pain scale used [37]. The termination criterion is the limit of 500 m of pain-free walking distance (PFWD), but there are additional endpoints: voluntary exhaustion, fatigue and shortness of breath, and severe pain in another part of the body (e.g., spine). The claudication pain scale is a continuous scale from 0—indicating no pain, to 4—indicating severe pain, and patients are instructed to walk to near-maximal pain levels [37]. No encouragements will be given during the test. The test administrator has the necessary qualifications and is familiar with the protocol.

 PFWD

6-min walk test (6MWT)

The 6MWT is a performance-based measure that evaluates the functional capacity of the individual to walk over a total of 6 min on a 100 ft (≈30 m) hallway, providing information regarding all the systems during physical activity [35]. The participants will be instructed to walk back and forth along the hallway to achieve the greatest distance possible. The participants will be allowed to stop and rest while the stopwatch continues to run. The American Thoracic Society guidelines will be used [38]. No encouragement through standardized verb phrases will be given because the aim is for the test to be as similar as possible to what happens in a real environment.

Secondary outcomes

Measure

Brief description

 Physical and Mental Quality of Life

Short-Form Health Survey (SF-36)

This instrument consists of 36 items with different response scales assessing eight health concepts: limitations in physical activities because of health problems,limitations in social activities because of physical or emotional problems, limitations in usual role activities because of physical health problems, bodily pain, general mental health (psychological distress and well-being), limitations in usual role activities because of emotional problems, vitality (energy and fatigue), and general health perceptions. The SF-36 has been widely used in studies with this population and has excellent psychometrics [39, 40].

 Vascular Disease-specific Quality of Life

Vascular Disease-Specific Quality of Life Questionnaire (VAscuQoL-6)

This is a specific measure of health-related QoL for patients with PAD, consisting of six items with different response scales [41, 42]. The total score ranges from 6 to 24, with higher results corresponding to a  higer quality of life associated with arterial disease. The Brazilian-Portuguese version of the VascuQoL-6 presents adequate valid and reliable indicators allowing its use in patients with PAD with intermittent claudication symptoms [43].

 Walking difficulties

Walking Impairment Questionnaire (WIQ)

This instrument assesses walking performance/abilities in three domains: distance (distances the individual can walk), speed (the speed the individual can walk), and stairs (number of stairs that the individual can climb without stopping), in a 5-point Likert scale (“none, slight, some, quite difficult, unable”). The distance comprises 7 items with a total score ranging from 0 to 28, with the highest results corresponding to a greater walked distance; speed has 4 items with a total score ranging from 0 to 16, with higher values indicating greater speed; stairs contain 3 items with a total score ranging from 0 to 12, with higher results indicating a greater ability to climb stairs [44]. The Brazilian-Portuguese version of the WIQ showed significant correlations between the WIQ domains and the SF-36 (functional capacity, physical aspects, bodily pain, and emotional aspects) and physical fitness performance (treadmill and strength tests). Intraclass coefficient correlation ranged from 0.72 to 0.81, and there were no differences in WIQ scores between the two questionnaire applications [45].

Process variables

Measure

Brief description

 Illness representations

Illness Perception Questionnaire - Brief (IPQ-B)

This questionnaire contains 8 items assessing the cognitive and emotional representations of the disease in eight specific dimensions: consequences, timeline, personal control, treatment control, identity, concerns, understanding, and emotional representations [46, 47]. The response scale for each item ranges from 0 to 10 and higher scores indicate more threatening perceptions in each item/dimension concerning PAD. The Portuguese version showed good internal consistency [48]. This instrument has already been used in studies with this population.

 Motivation stage for the change

Stages of Change in Exercise Questionnaire (SCEQ)

This questionnaire is composed of five items that represent each of the five stages of the Transtheoretical Model [49]. The Pre-Contemplation stage is characterized by the absence of intention to change behavior in the next 6 months (e.g., I do not walk, and I do NOT intend to start walking in the next 6 months). Contemplation is defined as the intention to change behavior within the next 6 months. When the individual intends to initiate behavior change within 1 month, the individual is classified as being in the Readiness to the Action stage. The Action stage is distinguished by having initiated a consistent and continued behavior change for 6 months or more and by moving the individual to the Maintenance stage. Subjects should indicate which item reflects their current exercise behavior in a dichotomous format of yes or no [50,51,52].

 Locus of causality for exercise

Locus of Causality for Exercise Scale (LCES)

This scale comprises three items assessing the perceived choice (or autonomy) regarding performing physical exercise. Thus, this scale assesses the extent to which individuals feel that they freely choose to exercise (walking) rather than feeling that they have to for some reason, addressing the source of the initiation of behavior. An internal locus of causality is evident when an individual engages in a behavior freely and with no sense of coercion. The response scale on a 6-point Likert scale ranges from 1 to 6 and the total score ranges from 3 to 18. Higher scores indicate greater self-determination or a more internal perceived locus of causality [53]. The Portuguese version showed good internal consistency [54].

 Planned behavior

Questionnaire of Planned Behavior on PAD-Walking (QPBPW)

This questionnaire assesses intentions, attitudes, subjective norms, perceived control, action, and coping plans regarding walking, in patients with PAD. The intentions scale is composed of 2 items with scores ranging from 2 to 10 points and higher scores indicating greater intention to perform the exercise (walking). The attitudes scale consists of 5 items, with scores ranging from 5 to 25 points and higher scores indicating a more positive attitude towards exercise. The subjective norms scale is composed of 3 items with scores ranging from 3 to 15 points, in which the higher the score, the higher is the perception of the importance attributed by other people to exercise. The perceived behavioral control scale evaluates the perception of control over-exercise, and it is composed of 4 items, with scores ranging from 4 to 20 points, and higher scores indicating a greater perceived behavioral control. The action and coping planning scale consist of 9 items, with scores ranging from 9 to 45 points, and higher scores indicating more action and coping plans regarding exercise (adapted for walking) [55]. The instrument has good internal consistency and was originally developed to be used with individuals with type 2 diabetes, and in this study, it was adapted to be used with patients with PAD, regarding walking.

 Satisfaction of basic psychological needs

Basic Psychological Needs in Exercise Scale (BPNES)

This scale consists of 12 items and assesses the perception of satisfaction of the three basic psychological needs in the context of the exercise: autonomy, competence, and positive relationship (relatedness) on a 5-point Likert scale (“strongly disagree” to “strongly agree”). Scores range from 12 to 60 and higher scores indicate a greater perceived satisfaction of psychological needs during exercise [56, 57]. The Portuguese validation was performed on a sample of regular exercise participants and showed good psychometric properties in the three scales. For this study, the instructions were adapted to walking behavior.

 Self-regulation in exercise

Behavioral Regulation in Exercise Questionnaire (BREQ-3)

This scale has 18 items, divided into six scales, assessing motivational regulations for exercise with a score ranging from 0 to 12 for each type of regulation on a 5-point Likert scale (“strongly disagree” to “strongly agree”). Higher scores indicate higher levels of one of the following types of behavioral regulation: amotivation, external, introjected, identified, integrated, and intrinsic [58,59,60]. The Portuguese validation was carried out on a sample of gym practitioners and showed good psychometric qualities in the six scales/types of motivation and regulation. For this study, the instructions were adapted to walking behavior.

Screening measures

Measure

Brief description

 Sociodemographic and clinical data

Sociodemographic and clinical data questionnaire

It consists of information to be obtained directly from participants or clinical records: gender, age, living environment, marital and professional status, rural or urban areas of residence. Clinical data: clinical and surgical history, chronic medication, and lifestyle behaviors (alcohol and tobacco consumption, hours of sleep, and the number of daily meals).

 Cognitive status

Mini-Mental State Examination (MMSE)

This is a widely used test of cognitive function, including tests of orientation, attention, memory, language, and visual-spatial skills. The total score ranges from 0 to 30, and higher results correspond to a better mental state. It will be applied at baseline as part of the screening assessment to ascertain exclusion criteria [61, 62].

 Emotional status

Geriatric Depression Scale-5 (GDS)

Geriatric Anxiety Scale (GAS)

As they are part of the screening, both questionnaires chosen to assess emotional state are very small, with dichotomous response scales, validated for a population over 65 years of age. Depressive symptoms are assessed through 5 items, with scores ranging from 0 to 5, and higher results corresponding to more depressive symptoms [63, 64]. A GDS-5 score ≥ 2 suggests clinical depression and the need for further evaluation. The Portuguese version has acceptable internal consistency. Anxiety symptoms are assessed through five items, with scores ranging from 0 to 5, and higher results corresponding to more anxiety symptoms [65, 66]. Portuguese internal consistency is high and a score ≥ 3 was optimal for the detection of DSM-IV Generalized Anxiety Disorder.

 Physical activity

International Physical Activity Questionnaire for elderly-Short Form (IPAQ-SF-E)

The version adapted for the elderly was used, as individuals with PAD avoid physical activity due to claudicating pain and it is not expected to find patients practicing high levels of physical activity or regular physical exercise. This version, although validated for people over 65 years old, is smaller and the items are more adapted to the performance level of this sample. Thus, this version consists of 4 self-reported moderate-to-vigorous physical activity (MVPA) and sedentary behavior (sitting) items. The items encompass the following behaviors, in the last 7 days: the time spent sitting, the days and time spent walking, the days and time spent in moderate-intensity activities, and the days and time spent in vigorous-intensity activities. Scores range from 0 to indefinite minutes of physical activity per week and higher results correspond to a greater amount of physical activity performed. Results can be reported in categories (low, moderate, or high activity levels) or as a continuous variable (MET minutes per week). MET minutes represent the amount of energy expended carrying out physical activity [67,68,69]. The specificity of IPAQ-SF-E to identify low-active participants was 85%, and the sensitivity to identify the more active participants was 81%.

Physical measures

Measure

Brief description

 Physical measures

Ankle-brachial-index (ABI)

Ankle Brachial Index (ABI) is the first low-cost diagnostic test for PAD [2]. The ABI is a simple and non-invasive test that will be obtained before and after the treadmill test by measuring the systolic pressures at the brachial artery, anterior tibial artery, and posterior tibial artery, in the supine position, in millimeters of mercury (mmHg), using a Doppler device. The ABI of each leg will be calculated by dividing the higher mean of three measures of the anterior tibial pressure or posterior tibial pressure by the higher mean of three measures of the right or left arm pressure (LifeDop 150 Doppler (8 MHz), USA).

 Hand strength

Hand grip strength (HGS)

Hand grip strength (HGS) is a basic measure for determining musculoskeletal function, as well as weakness and disability [70]. The HGS produces an isometric strength measure that allows the identification of the muscular weakness of the upper limb and provides an indication of the overall strength since it reflects the strength of the lower limbs. Three consecutive measures of handgrip strength (in kilograms (kg)), at both hands, will be recorded in a standing position with the arms next to the body, elbow slightly flexed and wrist in a neutral position, through a hand-held dynamometer (Gripx EH101, China).

 Body composition

Body composition measures

Weight (in kilograms), body mass index (kg/m²), body fat percentage (%), visceral fat level (%), skeletal muscle percentage (%), and resting metabolism (in kilocalories, kcal) will be measured through a bioimpedance scale (OMRON Body Composition Monitor BF511 (HBF-511 T-E/HBF-511B-E, Japan)). Height (in meters) will be measured using a tape measure.