IntroductionComplex post-traumatic stress disorder (CPTSD) is associated with dysregulation of the autonomic nervous system, measurable through heart rate variability (HRV); however, the impact of sensorimotor approaches on these markers remains poorly documented. This single-case study examines variations in HRV indices across a ten-session weekly protocol of Clay Field Therapy (CFT) in a 58-year-old woman with CPTSD (DSM-5, TEC, TADS-I) and multiple developmental traumas. The CFT process aligns with sensorimotor therapy principles and Herman's three-phase model of complex trauma treatment.MethodsHRV was recorded continuously using a portable ECG device and analyzed through time-synchronized segmentation across three session phases (trust and emotional stabilization, haptic work, meaning-making), through comparison of initial (3F) and final (3L) three-minute reference windows, and through identification of key autonomic windows. Global functioning was assessed with the WHODAS 2.0 pre- and post-treatment.ResultsMarked between-session HRV heterogeneity emerged alongside structured intra-session and longitudinal organization. Mean SDNN increased 3.7-fold across the protocol (S1: 55.3 ms to S10: 202.2 ms), paralleled by a 3.1-fold increase in mean RMSSD (26.5 ms to 81.1 ms). The three phases showed differentiated autonomic profiles: Phase 1 presented the highest parasympathetic values (RMSSD = 78.2 ms; mean SDNN = 154.4 ms, within normative range); Phase 2 reflected moderate sympathetic activation with preserved vagal modulation (SDNN = 140.9 ms; RMSSD = 60.1 ms); Phase 3 presented the highest mean HR (92.3 bpm) and a corrected mean SDNN of 129.8 ms approaching the lower normative boundary. Session 10 was structurally distinct, exhibiting the highest SDNN and RMSSD of the protocol alongside two temporally organized peaks (SDNN = 460 ms and 647 ms; LF/HF = 18.5 and 12.2) coinciding with HAPTIC-coded centering events. WHODAS 2.0 scores indicated a clinically meaningful improvement in global functional disability (48.1% to 37.1%), particularly in social participation.DiscussionThese findings suggest that CFT induces structured autonomic reorganization in CPTSD, with phase-differentiated profiles and session-level trajectories reflecting progressive regulatory capacity. HRV segmentation across therapeutic phases, combined with behavioral coding of haptic praxes, represents an original methodological framework for examining the psychophysiological mechanisms of clay therapy and provides a foundation for larger-scale controlled studies.