Self-myofascial release (SMR) is an intensive self-treatment with rigid foam rollers and other small handheld tools based on the exertion of compressive force to the soft tissue. Aiming to tackle dysfunctions of the skeletal muscle and connective tissue, it claims to mimic the effects of manual therapy techniques. Recent studies indicate that SMR, inter alia, improves range of motion (ROM) [
1‐
13] without concurrent decrease in neuromuscular performance [
1,
2,
5,
10‐
12]. In addition to neuronal mechanisms, such as increased stretch tolerance [
1,
3,
4], flexibility increases might be attributed to acute morphological adaptations:
First, the fasciae surrounding the muscles of the lower extremity are composed of multiple fibrous layers. Loose connective tissue enriched with hyaluronic acid [
14,
15] allows these layers to slide against each other during motion (e.g., contraction or elongation of the underlying muscle) [
14]. Several authors assume a positive effect of SMR on fascial sliding properties, e.g., through breaking up adhesions or loosening cross-links [
10,
16].
Another hypothesized morphological consequence of SMR is the alteration of passive tissue stiffness, as occurs after static stretching [
17‐
22]. A plethora of studies have demonstrated the existence of myofibroblasts (and their ability to impact stiffness) in fascia [
23,
24]. Moreover, according to in vitro experiments, fascial hydration has been shown to alter biomechanical tissue properties [
25]. Compression of the muscle and the surrounding fascial tissue (as occurs by the use of a foam roller) might hence stimulate contractile cell activity, affect tissue hydration [
10,
16] and microarchitecture of cell cytoskeleton [
26] or muscle filament mechanical properties [
27] and thereby alter tissue stiffness. Although these mechanisms seem plausible, there is no scientific evidence for these assumptions. Most studies focus solely on functional parameters (e.g., flexibility, strength, recovery) in practice-based settings. However, knowledge of the underlying physiological processes would allow a more effective selection of therapeutic and performance-related indications. The aim of the intended study is to evaluate the acute effects of SMR on the passive tissue stiffness of the anterior thigh muscles and the sliding properties of the associated fasciae. We hypothesize, that (1) SMR is able to decrease passive stiffness in the same manner as static stretching [
17‐
22], that (2) increased interlayer sliding of fascial layers occurs following treatment and (3) that these processes are associated with an increase in joint flexibility.