**1. Introduction**

Patients with peripheral arterial disease (PAD) often su ffer from intermittent claudication, leading to a significant walking impairment. According to the 2017 guidelines of the European Society of Vascular Surgery (ESVS), supervised exercise training is a Class I, Level A recommendation in patients presenting intermittent claudication, whereas unsupervised training is a Class I, Level C recommendation. Walking has thus been shown to be a safe and e ffective treatment for patients with PAD [1,2]. In particular, walking performance, cardiovascular parameters, and quality of life can be improved by exercise.

Some potential exercise e ffects and scheduling modifiers are still unclear, in particular, risk factors such as smoking, dyslipidemia, diabetes mellitus, obesity, and arterial hypertension as major comorbidities of PAD are only considered infrequently [3–6]. Physical activity has suppressive e ffects

on inflammation [7] and proinflammatory immune cells [8,9], as well as beneficial effects on endothelial function [10]. Additionally, physical training has the potential to promote an additional vascularization in hypoxic/ischemic tissues, such as the myocardium or peripheral limb [11]. Arteriogenesis, can be induced by exercise in human [12–14] and in animal studies [15]. The driving force of arteriogenesis is altered fluid shear stress (FSS) in the preformed collateral arteries due to increased blood flow [16]. The increased blood flow initiates vascular remodeling and diameter growth [17] and alters the miRNA profile [18].

Nevertheless, the physiological pathways of how exercise affects collateral growth at the molecular level are still not finally delineated.

Arteriogenesis is the process that results in growth of pre-existing collateral arterioles into functional collateral arteries, triggered by a hemodynamically relevant stenosis of supplying blood vessels. These bypassing vessels can sometimes be remarkably efficient and nearly completely replace the occluded arteries [19]. This formation is stimulated by an increase of shear stress on the endothelium [20]. An increase of blood flow can be achieved by a high demand and walking exercise gives the best possibility to maximize the flow physiologically [6].

In past decades various models have been developed that help in understanding the mechanisms of arteriogenesis. The ligation of the femoral artery (FAL) in mammals, especially the mouse, has become a well-established model for the induction of arteriogenesis [3,21,22]. Exercise stress tests are widely used for a variety of training protocols [23–25]. In most of the mice models, the training is voluntary (treadmill or running wheel), only a minor share of the protocols is forced. As exercise characteristics like frequency, intensity, type, and time cannot be controlled, a forced protocol may be appropriate. On the other hand, forced exercise is, unlike voluntary exercise, affected by distress [25–27].

The aim of this study was to find a suitable mouse model for simulating PAD as well as to establish a training protocol that would be accepted by cardiovascular-diseased animals and stimulate arteriogenesis. Such a protocol could provide the basis to methodically investigate effects of training on PAD at the molecular level in an experimental setup.
