Neural Contributions to Exercise-Induced Hypoalgesia With Blood Flow Restriction

Not Applicable

Recruiting

• Conditions: Healthy

• Registration Number: NCT07122011
• Lead Sponsor: University of Gran Rosario

Brief Summary

This experimental study explores the neurophysiological mechanisms associated with pain modulation following a single session of low-intensity resistance exercise combined with blood flow restriction (BFR) in healthy young adults. The study evaluates changes in sensory thresholds before and after the intervention using validated quantitative sensory testing (QST) methods. These include pressure pain thresholds, conditioned pain modulation, thermal thresholds, and temporal summation. The findings may contribute to a better understanding of the role of the nervous system in exercise-induced hypoalgesia, particularly in response to BFR protocols, with implications for future research in pain and rehabilitation.

Detailed Description

Exercise-induced hypoalgesia (EIH) is a physiological response characterized by reduced pain sensitivity following physical activity. Several central and peripheral mechanisms have been proposed to explain EIH, including activation of descending inhibitory pathways and peripheral nociceptor modulation. Blood flow restriction (BFR) training involves the application of controlled vascular occlusion during low-load exercise and has shown promising results in enhancing both muscle function and pain modulation.

This is a single-arm, pre-post experimental study involving healthy adults aged 18-35 years. All participants undergo a single session of low-intensity resistance exercise involving the lower limbs, performed under 60% limb occlusion pressure. Quantitative sensory testing (QST) is performed before and immediately after the intervention, including:

Pressure Pain Thresholds (PPT) measured with a digital algometer

Conditioned Pain Modulation (CPM) using cold-water immersion

Thermal thresholds assessed with a computer-controlled thermode

Temporal summation of pain via repeated pressure stimuli

The aim of this study is to explore the involvement of neurophysiological mechanisms-both central and peripheral-in the pain modulatory response following BFR exercise. This study is conducted at CUADI (Centro Universitario de Asistencia, Docencia e Investigación) in Rosario, Argentina. The results will contribute to basic science knowledge on pain physiology in healthy individuals and may inform future applied research in rehabilitation contexts.

Sample size considerations:

The estimated sample size is approximately 20 participants. This number is based on a preliminary power analysis conducted from pilot data on pressure pain threshold changes following cold water immersion, which showed a mean difference of 0.77 kgf with a standard deviation of 0.33 kgf. Using G\*Power software (v3.1), the calculated sample size for a paired comparison with 95% power and alpha of 0.05 was 16 subjects. To account for potential data loss or dropouts, we plan to include at least 20 individuals. This sample size is considered adequate for a mechanistic, single-arm pre-post design focusing on within-subject changes in pain modulation outcomes.

Study Timeline

• Status Verified: 2025-08
• Study Start: 2025-08-04
• Study First Submitted: 2025-08-06
• Study First Submitted QC: 2025-08-06
• Last Update Submitted: 2025-08-06
• Study First Posted: 2025-08-14
• Last Update Posted: 2025-08-14
• Primary Completion: 2025-10
• Study Completion: 2025-10-01

Recruitment & Eligibility

• Status: RECRUITING
• Sex: All
• Target Recruitment: 20

Inclusion Criteria

• Asymptomatic at the time of evaluation.
• Able to provide written informed consent.
• Available to attend a single evaluation and intervention session at the research center.

Exclusion Criteria

• Bilateral knee symptoms or suspected patellar tendinopathy.
• Increased symptoms with dynamic loading.
• Neurological disorders.
• Inflammatory rheumatic diseases.
• Cardiac diseases.
• Any surgery within the last 3 months.
• Pregnancy.
• Alcohol consumption on the day of participation.
• Hypertension (systolic blood pressure ≥140 mmHg).
• History of deep vein thrombosis.
• History of endothelial dysfunction.
• Peripheral vascular disease.
• Diabetes.
• Active infection.
• Spinal or referred pain.
• Previous experience with blood flow restriction (BFR) training.
• Overweight or obesity.

Study & Design

• Study Type: INTERVENTIONAL
• Study Design: SINGLE_GROUP

Primary Outcome Measures

Name	Time	Method
Conditioned pain modulation (CPM)	Baseline (before intervention) and immediately after the intervention session.	Changes in CPM will be assessed by immersing the hand up to the wrist in a cold water bath (0.6-0.8°) with a circulating water pump. The dominant arm for healthy will be immerse in the cold-water bath. In general, the conditioning stimulus will be applied for 2 min or maximum tolerance (whichever comes first). A computerized, custom-made visual analog scale (VAS) will be used to continuously track the response profile to conditional stimuli across participants during the application of CPM. A numeric rating scale ranging from 0 to 100, where 0 represents no perception, 30 represents pain threshold (defined as the time to reach a painful sensation at the predefined stimulation intensity) and 100 represents the tolerance threshold (defined as the sensation of pain when becomes intolerable). Before and immediately after the immersion, PPT measurements will be assessed on medial joint line of the dominant knee and dorsal forearm contralateral to the knee.
Pressure Pain Threshold (PPT)	At baseline and immediately after the intervention session.	Change in PPT will be assessed using a digital algometer (1 cm² round tip) applied perpendicularly to the skin at a rate of 1 kg/s until the participant first perceives pain. Three measurements will be averaged for each site. Sites: medial joint line of the dominant knee and dorsal forearm contralateral to the knee. Each measure will be performed at 30-second intervals.

Secondary Outcome Measures

Name	Time	Method
Thermal sensitivity thresholds	Immediately before and immediately after the intervention session.	Changes in heat perception thresholds (HDT, in ºC), and heat pain thresholds (HPT), and heat tolerance pain thresholds (HTPT) The heat stimuli will be applies over on the volar aspect of the non-dominant forearm. Tests will be performed in randomized order. Stimuli will be delivered using a thermode with an 9 cm2 contact. The baseline temperature will be set at 30°C and the skin will be heated (HDT) at a rate of 1°C/sec until participants report the first sensation of heat, the pain sensation for the HPT and the pain tolerance for the HTPT (minimum temperature 0 °C; maximum temperature 50 °C). The thermode then will return to 30 °C at a rate of 5°/sec. A 30-s rest interval will be taken before the next measure. Each test will be repeated 3 times at each assessment point (30 s inter-stimulus interval).
Temporal Summation (TS) Score	Immediately before and immediately after the intervention session.	Changes in TS will be evaluated at the knee and forearm by delivering 10 consecutive pressure pulses at the previously determined PPT intensity, each lasting 1 second with a 1 second interval between pulses. Pain intensity will be rated for the first, fifth, and tenth pulse on a 0-100 numeric rating scale. TS score will be calculated as the difference between the tenth and first pulse ratings.

Trial Locations

Locations (1)

University Center for Assistance, Teaching and Research (CUADI); 🇦🇷 Rosario, Santa Fe, Argentina