VO2max and Substrate Crossover Point

NCT07799662 | Completed

• 1 other identifier: EskisehirTU-SBF-CK-04
• Study Type: interventional
• Target: 20
• Locations: 1 country
• Sites: 1

Brief Summary

This study aims to investigate the relationship between maximal oxygen uptake (VO2max) and the substrate crossover point during incremental exercise. A total of 20 physical education students are recruited to complete a maximal incremental treadmill test using the standard Bruce protocol. Indirect calorimetry is utilized to assess oxygen uptake (VO2), carbon dioxide production (VCO2), and energy substrate utilization patterns. The substrate crossover point is operationally defined at a respiratory exchange ratio (RER) threshold of 0.85, indicating the metabolic transition toward predominant carbohydrate oxidation. The primary objective is to evaluate how variations in aerobic capacity influence the timing, oxygen uptake, and heart rate (HR) responses at this metabolic transition threshold.

Conditions

Cardiorespiratory Fitness; Substrate Metabolism During Exercise; Metabolic Flexibility; Maximal Oxygen Uptake

Keywords

vo2max; Substrate Crossover Point; Metabolic Flexibility; Bruce Protocol; Indirect Calorimetry; Substrate Oxidation; Incremental Exercise; Respiratory Exchange Ratio (RER)

Outcome Measures

Primary Outcomes (2)

• Time to reach the substrate crossover point

  Measure Description: Elapsed time (in minutes) from the start of the incremental treadmill test (Bruce protocol) to the point where the respiratory exchange ratio (RER) reaches 0.85, indicating the metabolic crossover where carbohydrate oxidation becomes the predominant fuel source. Time Frame: Baseline (single exercise test session, Day 1) Unit of Measure: Minutes

  Time Frame: Baseline (single test session, Day 1)

• Relative oxygen uptake at the crossover point

  Measure Title: Relative oxygen uptake at the substrate crossover point Measure Description: Oxygen uptake (VO2) normalized to body weight (mL/kg/min) recorded at the moment the substrate crossover point (respiratory exchange ratio \[RER\] = 0.85) is reached during the maximal incremental treadmill test (Bruce protocol). Time Frame: Baseline

  Measure Description: Measured continuously during the incremental exercise test using indirect calorimetry, recorded specifically at the point where the respiratory exchange ratio (RER) reaches 0.85. Time Frame: Baseline

Secondary Outcomes (3)

• Percentage of VO2max at the crossover point

  Measure Description: Relative oxygen uptake (VO2) at the substrate crossover point (respiratory exchange ratio [RER] = 0.85) expressed as a % of the participant's maximal oxygen uptake (VO2max), calculated upon completion of the Bruce protocol

• Heart rate at the crossover point

  Measure Description: Heart rate (HR) in beats per minute (bpm) measured continuously during the incremental treadmill test (Bruce protocol), recorded at the substrate crossover threshold (respiratory exchange ratio [RER] = 0.85). Time Frame: Baseline

• Maximal oxygen consumption (VO2max)

  Measure Description: Relative maximal oxygen uptake (VO2max in mL/kg/min) assessed at maximal exertion at the end of the Bruce protocol treadmill test to voluntary exhaustion via indirect calorimetry. Time Frame: Baseline

Study Arms (1)

Exercise Testing Group

EXPERIMENTAL

: Healthy young adult participants who undergo a single maximal incremental treadmill exercise test using the Bruce Protocol to assess cardiorespiratory fitness (VO2max) and substrate crossover kinetics.

Behavioral: Incremental Graded Exercise Test (Bruce Protocol)

Interventions

Incremental Graded Exercise Test (Bruce Protocol) BEHAVIORAL

Participants perform a maximal treadmill exercise test following the standardized Bruce Protocol. The test begins with a warm-up, followed by progressive 3-minute stages with continuous increases in speed and incline until voluntary exhaustion. Indirect calorimetry is used continuously via breath-by-breath gas analysis to measure VO2VCO2, and RER for substrate crossover determination.

Also known as: Bruce Treadmill Protocol, Maximal Incremental Exercise Test, Graded Exercise Testing (GXT), Maximal Treadmill Exercise Test

Exercise Testing Group

Eligibility Criteria

• Age: 18 Years - 30 Years
• Sex: all
• Healthy Volunteers: Yes
• Age Groups: Adult (18-64)

You may qualify if:

• Healthy male or female physical education students aged 18 to 30 years
• Regularly physically active (participating in structured physical activity at least 3 days per week)
• Medically cleared and capable of performing maximal graded treadmill exercise testing to voluntary exhaustion
• Willing and able to provide written informed consent

You may not qualify if:

• History of cardiovascular, pulmonary, metabolic, renal, or neuromuscular disorders
• Acute musculoskeletal injury or orthopedic condition that impairs treadmill running or maximal exertion
• Current use of prescription medications, stimulants, or dietary supplements known to alter metabolic rate, heart rate, or substrate oxidation
• Use of tobacco, nicotine products, or alcohol within 24 hours prior to testing
• Consumption of caffeine or vigorous physical exercise within 24 hours prior to the exercise trial

Sponsors & Collaborators

• Celil Kaçoğlu: lead

Study Sites (1)

Eskişehir Technical University

Eskişehir, Tepebaşi, 26100, Turkey (Türkiye)

Location

Related Publications (1)

• Bruce RA, Kusumi F, Hosmer D. Maximal oxygen intake and nomographic assessment of functional aerobic impairment in cardiovascular disease. Am Heart J. 1973 Apr;85(4):546-62. doi: 10.1016/0002-8703(73)90502-4. No abstract available.

  PMID: 4632004 BACKGROUND

Study Officials

• celil kaçoğlu, Ph.D.

  Eskişehir Teknik Üniversitesi

  PRINCIPAL INVESTIGATOR

Study Design

• Study Type: interventional
• Phase: not applicable
• Allocation: NA
• Masking: NONE
• Masking Details: Not applicable. This is an unblinded (Open Label) physiological performance study where all participants and investigators are fully aware of the exercise testing protocol and procedures.
• Purpose: BASIC SCIENCE
• Intervention Model: SINGLE GROUP
• Sponsor Type: OTHER
• Responsible Party: SPONSOR INVESTIGATOR
• PI Title: Assoc. Prof. Dr.

Model Details: This study utilizes a single-arm, continuous-variable design. All eligible participants undergo a single-visit testing session consisting of anthropometric measurements followed by a standardized incremental graded exercise test using the Bruce treadmill protocol until voluntary exhaustion. Because the main objective is to evaluate physiological relationships-specifically, how varying levels of maximal oxygen uptake (VO2max) correlate with the timing and oxygen cost of the substrate crossover point-all participants receive the same exercise stimulus and assessment procedures, serving as their own control across exercise intensity stages. No comparative control group or parallel group stratification is required.

Study Record Dates

• First Submitted: August 25, 2026
• First Posted: September 2, 2026
• Study Start: May 1, 2026
• Primary Completion: June 30, 2026
• Study Completion: July 15, 2026
• Last Updated: September 2, 2026

Record last verified: 2026-08

Data Sharing

• IPD Sharing: Will not share

Locations

TU (1)