Background <p>At least one-third of older people experience falls each year, often resulting in a fear of falling that leads to a cycle of negative consequences. Fear of falling activates the amygdala, which triggers a complex response involving cognitive, physiological, and behavioral components. Physiologically, the stress response includes autonomic changes like increased heart rate and reduced Heart Rate Variability (HRV). Behaviorally, heightened alertness leads to fight, flight, or freeze responses, influenced by amygdala and Periaqueductal Gray activations. In conditions like post-fall syndrome fear of falling leads to freezing, involving motor rigidity and disrupted motor control.</p> Methods <p>This protocol aims to objectively assess fear of falling in older patients with post-fall syndrome by measuring HRV in various conditions and compare these data with short FES-I results. A gap between physiological and self-reported measures could be reported. The secondary objective will be to measure the potential increase in muscle activation during fear. Hypotheses are that HRV changes will reflect fear levels and muscle activation will increase with fear. At least 30 patients recruited in geriatric care facility, with post-fall syndrome will be included in this study. Heart Rate Variability (HRV) and Electro-Myo-Graphy (EMG) of trapezoids muscles will be measured during initial sitting position and two stand-up positions with and without worktop (involving postural threat). The primary outcome will be the Root Mean Square of successive RR interval differences (RMSSD). Secondary outcome will include standard deviation of normal-to-normal intervals (SDNN), percentage of successive RR intervals with difference bigger than 50 ms (pNN50), low-frequency power (LF) and high-frequency power (HF), short-term analysis (SD1), as well as Root Mean Square (RMS) muscle activity. All these outcomes will be computed relatively to the control condition (i.e. slow effortless breathing). ANCOVA based on HRV and EMG will assess the differences across positions, and correlation between HRV and EMG will be investigated. Key variables, such as orthostatic hypotension and depressive status, will be considered as co-variables.</p> Discussion <p>If successful, the results could highlight some discrepancies between self-reported and physiological measures of fear and support the use of HRV as an emotional marker for fear of falling during rehabilitation. This would offer a valuable tool for tailoring sessions to patients’ anxiety levels, using a simple ECG sensor in clinical practice.</p> Trial registration <p>2024A0093542.</p>