NONLINEAR HEART RATE DYNAMICS IN ELDERLY WOMEN: RELATIONSHIP WITH POSTURAL BALANCE IN SELF-REPORTED FATIGUE

• Grant number: 24/14799-5
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: February 01, 2025
• End date: December 31, 2025
• Field of knowledge: Health Sciences - Physiotherapy and Occupational Therapy
• Principal Investigator: Luiz Carlos Marques Vanderlei
• Grantee: Elvis Colombo
• Host Institution: Faculdade de Ciências e Tecnologia (FCT). Universidade Estadual Paulista (UNESP). Campus de Presidente Prudente. Presidente Prudente , SP, Brazil

Abstract

Introduction: Elderly people are more vulnerable to falls and postural balance (PB) is of great importance in this context. The autonomic nervous system (ANS), which can be assessed through heart rate variability (HRV), is involved in the control of PB. However, studies that have considered this relationship between ANS and PB in fatigue conditions are scarce, even though fatigue is a prevalent symptom in routine activities of the elderly population that favors the increased risk of falls. Objective: To analyze the relationship between the nonlinear dynamics of heart rate and PB of elderly women in a state of self-reported fatigue (SRF) induced by the 6-minute step test (6ST). Methods: This is a cross-sectional observational study that will evaluate elderly women (¿ 60 years) considering two stages. In the first stage, information will be collected to characterize the sample and the volunteers will be familiarized with the 6ST. In the second stage, the heart rate will be recorded beat by beat using a heart rate monitor for 30 minutes (in the supine position) for subsequent analysis of the heart rate dynamics using: symbolic analysis (indices: 0V% - sympathetic modulation; 1V% - global variability; 2LV% and 2ULV% - parasympathetic modulation; Shannon entropy - complexity of the RR interval series), recurrence plot [indices: sample entropy (SampEn) and approximate entropy (ApEn) - complexity of the RR interval series] and trend-purified fluctuations (indices: DFA-total - complexity of the RR interval series; Alpha-1 and Alpha-2 - linearity of the RR interval series). Furthermore, in the second stage, the PB will be assessed at rest and under the SRF state (report ¿ 5 on the visual analogue scale for fatigue immediately after the 6ST) using the force platform. The PB will be determined based on the Root Mean Square (RMS), velocity, displacement and Multi-scale Entropy outcomes of the center of pressure. The Kolmogorov-Smirnov test will be used to assess the normality of the data. The Pearson or Spearman correlation tests will be used to analyze the relationship between the non-linear HRV indices and the absolute variations in PB. If there are significant relationships, unadjusted and adjusted linear regression will be performed (use of beta-blocker medication, body mass index, age and level of moderate to vigorous physical activity). The significance level will be set at p<0.05.