Acute Autonomic Responses During and After BFR Training (HOLD TIGHT)

Acute Cardiac Autonomic Responses During And Following Low-Intensity Blood Flow Restriction Resistance Exercise Versus Conventional High-Intensity Resistance Training In Young And Older Adults

The goal of this clinical trial is to compare how the body's nervous system responds to two different types of leg exercise in young and older adults. One type is low-intensity exercise with blood flow restriction (BFR) , where a cuff partially reduces blood flow to the legs during exercise. The other type is traditional high-intensity resistance training (HIRT), which uses heavier weights.

The main questions it aims to answer are:

Does low-intensity exercise with BFR cause less stress on the nervous system during exercise compared to high-intensity training? Does low-intensity exercise with BFR lead to faster recovery of the nervous system after exercise compared to high-intensity training? Do these responses differ between young adults and older adults? Researchers will compare low-intensity exercise with BFR to high-intensity training to see which approach is gentler on the nervous system during and after exercise.

Participants will:

Attend three visits to the research lab Complete a strength test on leg exercise machines Perform two separate exercise sessions: one with low-intensity exercise and BFR, and one with high-intensity training Have their heart rate, blood pressure, and heart rate variability monitored continuously during and after each exercise session

Study Overview

• Status: Not yet recruiting
• Conditions: Aging; Blood Flow Restriction Exercise
• Intervention / Treatment: Other: Low-Intensity Resistance Training with Blood Flow Restriction (LIRT-BFR); Other: High-Intensity Resistance Training (HIRT)

Detailed Description

This is a single-center, prospective, randomized crossover trial with two parallel age groups: young adults (19-24 years) and older adults (60 years and above). The study will be conducted at the Integrative Movement in Networking Systems Laboratory (IMOVE-NET), located at the Physiotherapy Clinic of Egas Moniz School of Health & Science (Almada, Portugal), between October 2026 and June 2027.

All participants will complete three visits, each separated by at least 48 hours to allow for recovery and minimize carryover effects. The first visit serves as a familiarization session, during which participants will have baseline cardiovascular measurements taken, become acquainted with the exercise protocol, and undergo one-repetition maximum (1RM) testing for the bilateral leg press and knee extension exercises. Body composition measurements will also be collected. Participants are instructed to avoid caffeine and alcohol for 24 hours, refrain from vigorous physical activity for 24 hours, and fully void before each session.

Following the familiarization visit, participants are randomly assigned to the order in which they will receive the two experimental conditions: (1) low-intensity resistance training with blood flow restriction (LIRT-BFR), and (2) high-intensity resistance training (HIRT). The randomization sequence will be generated using a web-based tool, placed in sequentially numbered, opaque, sealed envelopes, and concealed until the day of each visit. Simple randomization will be performed separately within each age group, generating independent session-order sequences for older and younger participants.

Each experimental session begins with a 15-minute resting phase in a supine position, during which heart rate and blood pressure are recorded. Beat-to-beat systolic and diastolic blood pressure will be recorded using finger plethysmography (Finapres Nova), and R-R intervals will be sampled at 300 Hz via the integrated 5-lead electrocardiogram (ECG) module. Intermittent brachial blood pressure readings from the contralateral arm (SunTech Tango+ automated auscultatory sphygmomanometer) will validate continuous Finapres measurements, particularly during exercise conditions. Continuous 2-minute segments of artifact-free R-R interval and systolic blood pressure (SBP) time series will be constructed for analysis.

Participants then perform the assigned exercise condition for approximately 30 minutes, consisting of bilateral knee extensions and leg curls. In the HIRT condition, participants perform 3 sets of 10 repetitions at 75% of 1RM with 2-minute rest intervals. In the LIRT-BFR condition, participants perform 4 sets of 20 repetitions at 30% of 1RM with a 5 cm wide pneumatic cuff applied to the most proximal portion of both thighs, inflated to 1.3 times the individual's ankle systolic blood pressure (SBP). The cuff remains inflated continuously throughout sets and rest periods and is released immediately after the final repetition. Exercise intensity, heart rate, rate of perceived exertion (RPE) using the modified Borg scale (0-10), and perceived discomfort are continuously monitored throughout both conditions. If a participant reports a discomfort score greater than 7, cuff pressure is immediately reduced from 1.3 to 1.2 times ankle SBP. If volitional fatigue prevents completion of repetitions, pressure is reduced to facilitate completion while maintaining a safe hemodynamic profile.

After each experimental condition, participants immediately return to the examination table and recover in a supine position for 60 minutes, during which blood pressure and heart rate are continuously re-evaluated. All data acquisition and offline analyses will follow relevant task force standards for heart rate variability and baroreflex sensitivity measurement.

The intervention will be administered by physiotherapy students who have completed 20 hours of technical training in exercise protocols and autonomic evaluation using the Finapres Nova system, maintaining an investigator-to-participant ratio of 2:1 to ensure safety and precision. Predefined stopping rules will be applied in the event of any adverse event or clinically relevant safety concern. The study supervisor will randomly review and audit 15% of total sessions to identify and correct procedural errors. Protocol adherence is strictly monitored and defined as the percentage of the prescribed protocol successfully completed; a minimum threshold of 70% will be required for any individual session to be considered valid for analysis.

• Study Type: Interventional
• Enrollment (Estimated): 48
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Xavier Melo, PhD; Phone Number: +351 212946700; Email: xmelo@egasmoniz.edu.pt

Study Locations

• Portugal
  • Monte Da Caparica
    • Almada, Monte Da Caparica, Portugal, 2829-511
      • Egas Moniz School of Health and Science
      • Contact: Xavier Melo, PhD; Phone Number: 00351212946700; Email: xmelo@egasmoniz.edu.pt

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

• Young adults aged 18-24 years
• Older adults aged 60 years and above
• Willing and able to provide written informed consent
• Able to comply with study procedures and visit schedule

Exclusion Criteria:

• Medications affecting cardiac activity (e.g., beta-blockers, calcium channel blockers, antiarrhythmics)
• Tobacco use
• Sleep apnea
• Body mass index (BMI) greater than 30 kg/m²
• Regular exercise training (more than 150 minutes per week for more than 6 months)
• History of coronary heart disease
• History of stroke
• History of oncological disease
• History of major cardiovascular events
• Peripheral vascular disease
• Uncontrolled hypertension
• Diabetes mellitus
• Unstable angina
• Active kidney or liver disease
• Chronic obstructive pulmonary disease (COPD)
• Recent surgical procedure (within the last two months)
• Neurological impairments affecting exercise capacity
• Orthopedic impairments affecting exercise capacity
• Sensory impairments affecting exercise capacity

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Supportive Care
• Allocation: Randomized
• Interventional Model: Crossover Assignment
• Masking: None (Open Label)

Number of Arms

3

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
No Intervention: No exercise or blood flow restriction
Experimental: Low-Intensity + Blood Flow Restriction	Other: Low-Intensity Resistance Training with Blood Flow Restriction (LIRT-BFR); Participants perform bilateral knee extensions and leg curls at 30% of their one-repetition maximum (1RM) while a pneumatic cuff is applied to the most proximal portion of both thighs. The cuff is inflated to 1.3 times the individual's ankle systolic blood pressure. The protocol consists of 4 sets of 20 repetitions with 30-second rest intervals between sets. Total exercise duration is approximately 30 minutes. Cuff pressure is maintained continuously throughout sets and rest periods and is released immediately after the final repetition.
Active Comparator: High-Intensity Resistance Training (HIRT)	Other: High-Intensity Resistance Training (HIRT); Participants perform bilateral knee extensions and leg curls at 75% of their one-repetition maximum (1RM). The protocol consists of 3 sets of 10 repetitions with 2-minute rest intervals between sets. Total exercise duration is approximately 30 minutes.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Changes in Time-Domain Heart Rate Variability Indices	Mean change from baseline in time-domain heart rate variability indices: RMSSD (root mean square of successive differences, reflecting vagal modulation), SDNN (standard deviation of normal-to-normal intervals, reflecting overall autonomic modulation), and pNN50 (percentage of successive R-R intervals >50 ms). These indices will be derived from continuous R-R interval recordings (Finapres Nova) during supine rest. Higher values indicate better parasympathetic modulation and autonomic flexibility.	Baseline (15-minute seated rest); during exercise (continuous throughout the 30-minute exercise bout); and 30 minutes into recovery (seated position)

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Changes in Frequency-Domain Heart Rate Variability Indices	Mean change from baseline in frequency-domain heart rate variability indices: low-frequency power (LF, ms²), high-frequency power (HF, ms²), and LF/HF ratio. Spectral analysis will be performed using a Daubechies-12 discrete wavelet transform on continuous R-R interval recordings (Finapres Nova) during supine rest. Higher HF indicates better parasympathetic modulation; lower LF/HF ratio indicates better sympathovagal balance.	Baseline (15-minute seated rest); during exercise (continuous throughout the 30-minute exercise bout); and 30 minutes into recovery (seated position)
Changes in Non-Linear Heart Rate Variability Indices	Mean change from baseline in non-linear heart rate variability indices derived from Poincaré plot analysis: SD1 (reflecting short-term variability, predominantly parasympathetic modulation), SD2 (reflecting long-term variability, overall autonomic modulation), and SD1/SD2 ratio. Derived from continuous R-R interval recordings (Finapres Nova) during supine rest.	Baseline (15-minute seated rest); during exercise (continuous throughout the 30-minute exercise bout); and 30 minutes into recovery (seated position)
Changes in Cardiovagal Baroreflex Sensitivity (BRS)	Mean change from baseline in baroreflex sensitivity (BRS) estimated using the spontaneous sequence method, which identifies concordant systolic blood pressure and R-R interval ramps. BRS gain is expressed as ms/mmHg. Higher BRS gain indicates better reflex integrity and better blood pressure stability.	Baseline (15-minute seated rest); during exercise (continuous throughout the 30-minute exercise bout); and 30 minutes into recovery (seated position)
Changes in Blood Pressure	Mean change from baseline in beat-to-beat systolic blood pressure (SBP) and diastolic blood pressure (DBP). Both measures will be derived from finger plethysmography (Finapres Nova) during supine rest, validated against brachial readings (SunTech Tango+). Units: mmHg. For SBP, higher values indicate higher cardiovascular load. For DBP, higher values indicate higher cardiovascular load.	Baseline (15-minute seated rest); during exercise (continuous throughout the 30-minute exercise bout); and 30 minutes into recovery (seated position)

Collaborators and Investigators

• Sponsor: Egas Moniz - Cooperativa de Ensino Superior, CRL

Publications and helpful links

General Publications

• Grassler B, Thielmann B, Bockelmann I, Hokelmann A. Effects of different exercise interventions on heart rate variability and cardiovascular health factors in older adults: a systematic review. Eur Rev Aging Phys Act. 2021 Nov 17;18(1):24. doi: 10.1186/s11556-021-00278-6.
• Oliveira RS, Vitor da Costa M, Pedro RE, Polito MD, Avelar A, Cyrino ES, Nakamura FY. Acute cardiac autonomic responses after a bout of resistance exercise. Sci Sports. 2012;27(6):357-364.
• Okuno NM, Pedro RE, Leicht AS, de Paula Ramos S, Nakamura FY. Cardiac autonomic recovery after a single session of resistance exercise with and without vascular occlusion. J Strength Cond Res. 2014 Apr;28(4):1143-50. doi: 10.1519/JSC.0000000000000245.
• Ganzarolli Stevanatto LC, Venturini Ferreira ML, Bonganha V, de Souza GV, Cavaglieri CR, Chacon Mikahil MPT. Acute cardiac autonomic responses to resistance exercise with and without blood flow restriction. Sci Sports. 2022;37(5-6):454-458. DOI: 10.1016/j.scispo.2022.04.001
• Ferreira MLV, Sardeli AV, Souza GV, Bonganha V, Santos LDC, Castro A, Cavaglieri CR, Chacon-Mikahil MPT. Cardiac autonomic and haemodynamic recovery after a single session of aerobic exercise with and without blood flow restriction in older adults. J Sports Sci. 2017 Dec;35(24):2412-2420. doi: 10.1080/02640414.2016.1271139. Epub 2016 Dec 28.

Study record dates

Study Major Dates

• Study Start (Estimated): October 5, 2026
• Primary Completion (Estimated): May 14, 2027
• Study Completion (Estimated): June 25, 2027

Study Registration Dates

• First Submitted: July 20, 2026
• First Submitted That Met QC Criteria: July 22, 2026
• First Posted (Actual): July 23, 2026

Study Record Updates

• Last Update Posted (Actual): July 23, 2026
• Last Update Submitted That Met QC Criteria: July 22, 2026
• Last Verified: July 1, 2026

More Information

Terms related to this study

• Keywords: older adults; recovery; resistance exercise; young adults; blood flow restriction; cardiovagal modulation
• Other Study ID Numbers: HOLD TIGHT 2.0

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES
• IPD Plan Description: Data obtained in this study may be provided to qualified researchers with academic interest in autonomic responses to resistance training with blood flow restriction. Data or samples shared will be coded, with no PHI included. Approval of the request and execution of all applicable agreements (i.e. a material transfer agreement) are prerequisites to the sharing of data with the requesting party.
• IPD Sharing Time Frame: Data requests can be submitted starting 9 months after article publication and the data will be made accessible for up to 24 months. Extensions will be considered on a case-by-case basis.
• IPD Sharing Access Criteria: Access to trial IPD can be requested by qualified researchers engaging in independent scientific research and will be provided following review and approval of a research proposal and Statistical Analysis Plan (SAP) and execution of a Data Sharing Agreement (DSA). For more information or to submit a request, please contact xmelo@egasmoniz.edu.pt
• IPD Sharing Supporting Information Type: STUDY_PROTOCOL

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No