Energy–Tissue Interaction in Physiotherapy: A Proposed Conceptual Framework for Electrophysical Agents

Electrophysical agents (EPAs) are widely used in rehabilitation, yet their selection is frequently guided by diagnostic labels, established protocols, or device-specific parameters, with comparatively limited consideration of how the delivered energy physically interacts with the intended target tissue. This narrative review examines energy–tissue interactions underlying six commonly used EPAs: therapeutic ultrasound, photobiomodulation (LASER), diathermy, capacitive–resistive electric transfer (TECAR/CRET), extracorporeal shockwave therapy (ESWT), and pulsed electromagnetic fields (PEMF). Relevant literature was identified through searches of PubMed and Scopus, prioritising publications from 2016 to 2026 while incorporating earlier foundational studies. Experimental investigations, computational models, and relevant reviews were narratively synthesised to examine energy propagation, attenuation, distribution, tissue-specific interactions, and the resulting physical and biological stimuli. Based on this synthesis, the Tissue Energy Interaction Framework (TEIF) is introduced as a proposed conceptual model requiring further validation rather than an established clinical decision-making tool. The framework describes a pathway from energy generation and delivery through tissue propagation, attenuation/distribution, target interaction, physical or biological stimulus, biological response, and potential clinical effect. The reviewed evidence indicates that tissue depth, composition, interfaces, and modality-specific characteristics substantially influence the physical stimulus reaching a therapeutic target. Energy penetration should therefore be distinguished from effective target interaction, while measurable interaction does not necessarily establish clinical effectiveness. The TEIF proposes that physical and biological plausibility should inform EPA selection alongside, but never supersede, evidence of clinical effectiveness and patient-specific considerations. Further research is required to validate the framework and determine whether tissue-informed EPA selection improves clinical outcomes.