## 1 Introduction
### Influence on the Skin  
The treatment head used in endermologie initiates this process by stimulating the skin surface while simultaneously sending signals to dermal and subcutaneous cells. Cell activation relies on signal transduction, a fundamental biological process that converts external stimuli into intracellular responses. This mechanism is essential for intercellular communication and the regulation of cellular functions. When the external stimuli are mechanical forces, this process is referred to as mechanotransduction (Figure 1). In the context of endermologie, mechanical stimulation applied to the skin is transmitted through the epidermis, dermis, and subcutaneous tissues, influencing both cell-cell and cell-extracellular matrix (ECM) interactions. This mechanotransduction plays a crucial role in tissue remodeling, as connective tissue cells adapt their ECM composition in response to mechanical stress. Cells exposed to such forces modulate protein expression, leading to functional and structural changes that help the tissue meet new mechanical demands [7]. The receptors of various types of cells are stimulated and, as a result, their kinetic and functional activity is increased (Figure 2). When keratinocytes, fibroblasts, endothelial cells, and other skin cells are mechanically stimulated, they release growth factors or cytokines, which, in turn, influence all structural and morphological modifications of the skin [9]. Under the influence of mechanical stimuli, i.e., mechanotransduction (Figure 3), numerous skin processes are activated, processes by which cells perceive mechanical stimuli and respond to them by converting them into biochemical signals. Studies prove that the mechanical stress of epithelial cells activates the transcription factors YAP1 and \(\beta\)-catenin and causes cell cycle triggering. Moreover, transcriptional activity is important for cell cycle rebirth and progression [4]. YAP1 regulates gene expression in response to mechanical tension through the Hippo pathway. \(\beta\)-catenin modulates cellular responses via the Wnt pathway, cooperating with YAP1. Both pathways influence tissue regeneration, fibroblast proliferation, and ECM remodeling, which are crucial in mechanical therapies such as endermologie [10]. Figure 1: Comparison of different mechanical tissue mobilization techniques used in aesthetic and therapeutic procedures. The illustrations depict variations in mechanical stimulation of the skin and subcutaneous tissues, highlighting different approaches to vacuum- and roller-based manipulation [8]. Figure 3: Mechanotransduction and cellular response to mechanical stimuli. External mechanical forces (shear stress, gravity, stiffness, stretch/strain) activate mechanoreceptors on the cell surface, triggering intracellular signaling pathways. This leads to gene transcription, affecting cellular behaviors such as proliferation, migration, apoptosis, and differentiation. Additionally, mechanotransduction influences extracellular matrix (ECM) remodeling, contributing to tissue restructuring and adaptation to mechanical stress. 1. Mechanotransduction; 2. Gene transcription; 3. Intracellular signalling; 4. ECM remodelling; 5. Strecth/strain. Figure 2: Mechanotransduction pathway in cellular activation. External mechanical stimuli (first messengers) are detected at the cell membrane, initiating transmembrane signal transfer and intracellular translation. This leads to the generation of secondary messengers, which trigger a cascade of biochemical reactions, ultimately resulting in a specific cellular response. This process is fundamental to mechanotransduction, the mechanism by which mechanical forces influence cell behavior and extracellular matrix remodeling. The mechanotransduction activates the specific receptors for free substances such as histamine, bradykinin, serotonin, and catecholamines, which act on beta-adrenergic receptors and activate adenyl cyclase and AMP. Then, protein kinase activates intra-adipocyte lipase to lipolysis.