Effect of Training Intensity on Microvascular Function

Effect of Continuous Versus High-intensity Interval Aerobic Training on the Muscular Vascular Adaptation

The aim of this trial is to investigate the effect of aerobic training intensity on muscle vascular function: continuous versus interval.

Study Overview

• Status: Completed
• Conditions: Sedentary Behavior; Vascular Remodeling; Hemodynamic Rebound
• Intervention / Treatment: Procedure: Percutaneous muscle biopsies of the vastus lateralis (quadriceps); Other: Measurement of the maximal oxygen uptake (VO2max); Other: Non-Invasive Cardiac Output Measurement (Innocor)

Detailed Description

This trial will compare the hemodynamic effects of aerobic training on muscle microvascular function between participants randomly assigned to one of two groups: a continuous training group and an high-intensity interval training group.

All data concerning the primary and secondary outcomes will be obtained at the start and repeated at the end of 8 weeks aerobic training.

• Study Type: Interventional
• Enrollment (Actual): 25
• Phase: Not Applicable

Contacts and Locations

Study Locations

• Belgium
  • Anderlecht
    • Brussels, Anderlecht, Belgium, 1070
      • Université Libre de Bruxelles, Faculté des Sciences de la motricité, Laboratoire de kinésithérapie

Participation Criteria

Eligibility Criteria

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

Description

Inclusion Criteria:

• Healthy female or male between 18 and 45 years
• Be sedentary
• Able to cycle
• Able to provide written informed consent

Exclusion Criteria:

• Have a pathology that may impact vascular function as :

  • cardiac pathology
  • pneumological pathology
  • metabolic pathology
• Smoke

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Basic Science
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: None (Open Label)

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Moderate-Intensity Continuous Training (MICT): 34 min at 65% maximal heart rate; Participants performed a 3-minute warm-up at 50% of their maximal heart rate (HRmax), as determined during baseline cardiopulmonary exercise testing (ergospirometry), followed by 40 minutes of continuous cycling at 65% of their VO₂max. Sessions were conducted three times per week for a total duration of 8 weeks.	Procedure: Percutaneous muscle biopsies of the vastus lateralis (quadriceps); Percutaneous muscle biopsies of the vastus lateralis (quadriceps) were performed under local anesthesia. Samples were collected at baseline and/or post-intervention to assess microvascular structure, fiber composition, and molecular adaptations to aerobic training.; Other: Measurement of the maximal oxygen uptake (VO2max); Cardiopulmonary Exercise Testing (CPET) Maximal oxygen consumption (VO₂max) was assessed using an incremental stepwise protocol on a cycle ergometer. Participants performed the test at baseline and after the 8-week training intervention. Respiratory gas exchange was continuously measured using a COSMED K5 portable metabolic system, which provided breath-by-breath analysis of oxygen uptake (VO₂), carbon dioxide production (VCO₂), and ventilation parameters. The test was terminated upon volitional exhaustion or when predefined criteria for VO₂max plateau were met.; Other: Non-Invasive Cardiac Output Measurement (Innocor); Maximal cardiac output was assessed at peak exercise intensity during cardiopulmonary exercise testing (CPET) using the Innocor device. This system employs the inert gas rebreathing technique, which involves the controlled inhalation of a gas mixture containing nitrous oxide (N₂O) and sulfur hexafluoride (SF₆). By analyzing the washout kinetics of these gases during rebreathing, the device estimates pulmonary blood flow, which is then used to calculate cardiac output non-invasively. Measurements were performed at the maximal workload reached during the incremental cycling test.
Experimental: High-Intensity Interval Training (HIIT): 2x2 min at 65% and 90% of maximal heart rate; Participants performed a 3-minute warm-up at 50% of their maximal heart rate (HRmax), as determined during baseline cardiopulmonary exercise testing (ergospirometry). The main training protocol consisted of alternating 2-minute cycling bouts: 2 minutes at 65% HRmax followed by 2 minutes at 90% HRmax, repeated continuously for a total of 28 minutes. Sessions were conducted three times per week over an 8-week period.	Procedure: Percutaneous muscle biopsies of the vastus lateralis (quadriceps); Percutaneous muscle biopsies of the vastus lateralis (quadriceps) were performed under local anesthesia. Samples were collected at baseline and/or post-intervention to assess microvascular structure, fiber composition, and molecular adaptations to aerobic training.; Other: Measurement of the maximal oxygen uptake (VO2max); Cardiopulmonary Exercise Testing (CPET) Maximal oxygen consumption (VO₂max) was assessed using an incremental stepwise protocol on a cycle ergometer. Participants performed the test at baseline and after the 8-week training intervention. Respiratory gas exchange was continuously measured using a COSMED K5 portable metabolic system, which provided breath-by-breath analysis of oxygen uptake (VO₂), carbon dioxide production (VCO₂), and ventilation parameters. The test was terminated upon volitional exhaustion or when predefined criteria for VO₂max plateau were met.; Other: Non-Invasive Cardiac Output Measurement (Innocor); Maximal cardiac output was assessed at peak exercise intensity during cardiopulmonary exercise testing (CPET) using the Innocor device. This system employs the inert gas rebreathing technique, which involves the controlled inhalation of a gas mixture containing nitrous oxide (N₂O) and sulfur hexafluoride (SF₆). By analyzing the washout kinetics of these gases during rebreathing, the device estimates pulmonary blood flow, which is then used to calculate cardiac output non-invasively. Measurements were performed at the maximal workload reached during the incremental cycling test.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Percutaneous muscle biopsies of the vastus lateralis	Muscle tissue samples obtained from the vastus lateralis were processed using optical clearing and immunohistochemical staining techniques to visualize the microvascular network. Confocal microscopy was employed to acquire high-resolution three-dimensional images of arterioles, capillaries, and venules. Quantitative assessments included: Internal diameter measurements, based on endothelial cell boundaries (intima layer); External diameter measurements, based on smooth muscle cells and pericytes (media layer); Capillary density, determined by counting the number of capillaries per sample volume	At baseline and after completion of the 8-week intervention

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Cardiopulmonary Exercise Testing (CPET)	VO₂max was determined using a graded, incremental exercise test performed on a cycle ergometer until volitional exhaustion. Throughout the test, respiratory gases were continuously measured using a metabolic cart (e.g., COSMED K5), which provided breath-by-breath analysis. The following parameters were recorded : VO₂ (oxygen uptake) in mL/min; VCO₂ (carbon dioxide production) in mL/min; Minute ventilation (VE) in L/min	At baseline and after completion of the 8-week intervention
Maximal Cardiac Output Measurement Using Inert Gas Rebreathing (Innocor)	Innocor is a medical device that estimates cardiac output using the inert gas rebreathing technique, a validated non-invasive method. During the procedure, the participant inhales a gas mixture containing nitrous oxide (N₂O) and sulfur hexafluoride (SF₆) through a closed circuit. These inert gases are absorbed and eliminated at rates proportional to pulmonary blood flow. By analyzing the washout kinetics of these gases during a brief rebreathing period, Innocor calculates pulmonary blood flow, which is then used to estimate cardiac output. This measurement is typically performed at rest or at peak exercise intensity, such as during the final stage of a cardiopulmonary exercise test (CPET). The system provides real-time data on: Cardiac output (L/min); Stroke volume (ml/min); Heart rate (bpm); Pulmonary blood flow (L/min)	At baseline and after completion of the 8-week intervention

Collaborators and Investigators

• Sponsor: Université Libre de Bruxelles

Study record dates

Study Major Dates

• Study Start (Actual): January 22, 2022
• Primary Completion (Actual): August 15, 2024
• Study Completion (Actual): December 31, 2024

Study Registration Dates

• First Submitted: September 26, 2022
• First Submitted That Met QC Criteria: November 14, 2025
• First Posted (Actual): November 20, 2025

Study Record Updates

• Last Update Posted (Actual): November 20, 2025
• Last Update Submitted That Met QC Criteria: November 14, 2025
• Last Verified: October 1, 2025

More Information

Terms related to this study

• Keywords: Microcirculation; High-Intensity Interval Training; Quadriceps Muscle; Endurance Training; Hemodynamic Instability; Microvascular Density
• Additional Relevant MeSH Terms: Pathologic Processes; Pathological Conditions, Anatomical; Pathological Conditions, Signs and Symptoms; Behavior; Vascular Remodeling; Sedentary Behavior
• Other Study ID Numbers: ULB

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

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