Cardiorespiratory FitnessVO2MAX-CROSSNCT07799662
VO2max and Substrate Crossover Point
A study testing Incremental Graded Exercise Test (Bruce Protocol) in people with Cardiorespiratory Fitness and Substrate Metabolism During Exercise, run by Celil Kaçoğlu at 1 site in Turkey (Türkiye).
Trial 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. Read more about this study
- Who is it for?
- Ages 18 to 30 yearsHealthy volunteers can take part
- Conditions the study is for
- Cardiorespiratory Fitness, Substrate Metabolism During Exercise, Metabolic Flexibility
- What is being tested?
- Incremental Graded Exercise Test (Bruce Protocol)
- Type of treatment
- Lifestyle or therapy programme
- Could I receive a placebo?
- No, everyone receives an active treatment
- How many people
- 20 participants
- Where
- 1 siteTurkey (Türkiye)
- Study dates
- 1 May 2026to 15 Jul 2026
- Phase
- Interventional
- Are there results?
- None posted in the registry
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 18 to 30 years
- All sexes
- Healthy volunteers accepted
- Adult
Who may be able to join
- 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
Who cannot join
- 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
Trial locations and contacts
1 site in 1 country.
Turkey (Türkiye)1 site
Eskişehir Technical University
Eskişehir, Tepebaşi, 26100
About this study
Official title: Higher VO2max Delays Substrate Switching and Shifts the Crossover Point to Greater Oxygen Uptake During Incremental Exerciseebys
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.
Read the detailed description
This study evaluates the relationship between maximal oxygen uptake (VO2max) and the substrate crossover point during incremental treadmill exercise in young, physically active individuals. Substrate utilization kinetics and metabolic flexibility represent critical components of cardiovascular conditioning and endurance performance; however, the impact of continuous variations in aerobic capacity on the onset of metabolic transition requires detailed investigation.
Participants undergo anthropometric testing followed by a maximal graded exercise test on a motor-driven treadmill following the standard Bruce protocol. Breath-by-breath expired gas analysis using indirect calorimetry continuously monitors oxygen uptake (VO2), carbon dioxide production (VCO2), and minute ventilation (VE) throughout the test. Respiratory exchange ratio (RER) values are calculated continuously. The substrate crossover point is operationally defined as the exercise intensity corresponding to an RER threshold of 0.85, representing the metabolic transition where carbohydrate oxidation becomes the predominant contributor to total energy expenditure over lipid oxidation.
Key outcome measures extracted at this threshold include:
Time to reach the crossover point (minutes)
Absolute oxygen uptake at crossover (liters per minute [L/min])
Relative oxygen uptake at crossover (milliliters per kilogram per minute [mL/kg/min])
Percentage of maximal oxygen uptake at crossover (%VO2max)
Heart rate at crossover (beats per minute [bpm])
Statistical associations between maximal aerobic capacity (VO2max) and the primary outcome measures at the crossover point are analyzed using linear correlation and regression models to determine how cardiorespiratory fitness alters substrate switching kinetics under progressive physical strain.
- Conditions
- Cardiorespiratory Fitness, Substrate Metabolism During Exercise, Metabolic Flexibility, Maximal Oxygen Uptake
- Being tested
- Incremental Graded Exercise Test (Bruce Protocol)
- Keywords
- vo2max, Substrate Crossover Point, Metabolic Flexibility, Bruce Protocol, Indirect Calorimetry, Substrate Oxidation, Incremental Exercise, Respiratory Exchange Ratio (RER)
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
Incremental Graded Exercise Test (Bruce Protocol)Behavioural
Also called Bruce Treadmill Protocol, Maximal Incremental Exercise Test, Graded Exercise Testing (GXT), Maximal Treadmill Exercise Test
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.
| Study group | Role | What they receive |
|---|---|---|
| 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. Receives: Behavioral: Incremental Graded Exercise Test (Bruce Protocol) |
What is being measured
The primary outcome is the main question the study is designed to answer.
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
Measured: 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
Measured: 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 Title: Percentage of maximal oxygen uptake at the substrate crossover point
Measure Description: Relative oxygen uptake (VO2) at the substrate crossover point (respiratory exchange ratio [RER] = 0.85) expressed as a percentage (%) of the participant's maximal oxygen uptake (VO2max) during the Bruce protocol treadmill test.
Time Frame: Baseline
Measured: 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 Title: Heart rate at the substrate crossover point Measure Description: Heart rate (HR) recorded in beats per minute (bpm) using a telemetric heart rate monitor at the point where the substrate crossover threshold (respiratory exchange ratio [RER] = 0.85) is achieved during the maximal incremental treadmill test (Bruce protocol).
Time Frame: Baseline
Measured: 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:
The highest rate of relative oxygen uptake (VO2 in mL/kg/min) attained during the maximal graded exercise test (Bruce protocol) to voluntary exhaustion via indirect calorimetry.
Time Frame: Baseline
Measured: 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
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted2 Sep 2026
- Study start1 May 2026
- Primary completion30 Jun 2026
- Study completion15 Jul 2026
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Publications (1)Papers the sponsor has linked to this study.
- Other trials for Cardiorespiratory FitnessStudies of the same condition, open and under way.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Interventional
- Phase
- Phase N/A
- Primary purpose
- Basic science
- Allocation
- Not applicable
- Intervention model
- Single group
- Model description
- 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.
- Masking
- None (open label)
- Enrolment
- 20 participants (actual)
Sponsor and investigators
- Lead sponsor
- Celil Kaçoğlu
- Sponsor type
- University, hospital or other
- Responsible party
- Sponsor-investigator, Celil Kaçoğlu, Eskisehir Technical University
- Investigators
- celil kaçoğlu, Ph.D., Principal investigator, Eskişehir Teknik Üniversitesi
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT07799662
- Sponsor's protocol ID
- EskisehirTU-SBF-CK-04
- Acronym
- VO2MAX-CROSS
- Status last verified
- Aug 2026
- First submitted
- 25 Aug 2026
- Last updated
- 2 Sep 2026
- Results posted
- No
- Data monitoring committee
- No
- FDA-regulated drug
- No
- FDA-regulated device
- No
- Individual data sharing
- No: Individual participant data will not be publicly shared due to privacy and ethical constraints aimed at protecting participant confidentiality. However, de-identified aggregated data or specific data sets may be made available from the corresponding author upon reasonable academic request.
Publications
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.
PubMed 4632004
Study at a glance
From the registry record, last updated by the sponsor on 2 Sep 2026. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- Higher VO2max Delays Substrate Switching and Shifts the Crossover Point to Greater Oxygen Uptake During Incremental Exerciseebys
- ClinicalTrials.gov ID
- NCT07799662
- Acronym / sponsor ID
- VO2MAX-CROSS / EskisehirTU-SBF-CK-04
- 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)
- Study type
- Interventional
- Recruitment status
- Completed
- Enrolment
- 20 participants (actual)
- Lead sponsor
- Celil KaçoğluUniversity, hospital or other
- Study start
- 1 May 2026 (actual)
- Primary completion
- 30 Jun 2026 (actual)
- Study completion
- 15 Jul 2026 (actual)
- First posted
- 2 Sep 2026 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
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.
Detailed description
This study evaluates the relationship between maximal oxygen uptake (VO2max) and the substrate crossover point during incremental treadmill exercise in young, physically active individuals. Substrate utilization kinetics and metabolic flexibility represent critical components of cardiovascular conditioning and endurance performance; however, the impact of continuous variations in aerobic capacity on the onset of metabolic transition requires detailed investigation.
Participants undergo anthropometric testing followed by a maximal graded exercise test on a motor-driven treadmill following the standard Bruce protocol. Breath-by-breath expired gas analysis using indirect calorimetry continuously monitors oxygen uptake (VO2), carbon dioxide production (VCO2), and minute ventilation (VE) throughout the test. Respiratory exchange ratio (RER) values are calculated continuously. The substrate crossover point is operationally defined as the exercise intensity corresponding to an RER threshold of 0.85, representing the metabolic transition where carbohydrate oxidation becomes the predominant contributor to total energy expenditure over lipid oxidation.
Key outcome measures extracted at this threshold include:
Time to reach the crossover point (minutes)
Absolute oxygen uptake at crossover (liters per minute [L/min])
Relative oxygen uptake at crossover (milliliters per kilogram per minute [mL/kg/min])
Percentage of maximal oxygen uptake at crossover (%VO2max)
Heart rate at crossover (beats per minute [bpm])
Statistical associations between maximal aerobic capacity (VO2max) and the primary outcome measures at the crossover point are analyzed using linear correlation and regression models to determine how cardiorespiratory fitness alters substrate switching kinetics under progressive physical strain.
Study design
- Primary purpose
- Basic science
- Allocation
- Not applicable
- Intervention model
- Single group
- Masking
- None (open label)
- Number of arms
- 1
- Model description
- 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.
| Arm | Type | Receives |
|---|---|---|
| Exercise Testing Group | Experimental | Behavioral: Incremental Graded Exercise Test (Bruce Protocol): 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. |
Who may qualify
- Ages
- 18 to 30 years
- Sex
- All
- Healthy volunteers
- Accepted
- Age groups
- Adult
Key inclusion criteria (4 listed)
- 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
Key exclusion criteria (5 listed)
- 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
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| Incremental Graded Exercise Test (Bruce Protocol)Also: Bruce Treadmill Protocol, Maximal Incremental Exercise Test, Graded Exercise Testing (GXT), Maximal Treadmill Exercise TestParticipants 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. | Behavioural | Exercise Testing Group |
Primary outcome
Time to reach the substrate crossover point
Time frame: Time Frame: Baseline (single test session, Day 1)
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
Relative oxygen uptake at the crossover point
Time frame: 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
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
3 secondary outcomes
Percentage of VO2max at the crossover point
Time frame: 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
Time frame: 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)
Time frame: 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
Results and safety
The study is completed, but results are not available in the source record. That does not mean the treatment did or did not work.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 2 Sep 2026.
- Background: PubMed 4632004Bruce 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.
- Individual participant dataSharing planned: No. Individual participant data will not be publicly shared due to privacy and ethical constraints aimed at protecting participant confidentiality. However, de-identified aggregated data or specific data sets may be made available from the corresponding author upon reasonable academic request.
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Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part. This study is not recruiting at the moment.
celil kaçoğlu, Ph.D. principal investigator
Eskişehir Teknik Üniversitesi
1 site in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A study testing Incremental Graded Exercise Test (Bruce Protocol) in people with Cardiorespiratory Fitness and Substrate Metabolism During Exercise, run by Celil Kaçoğlu at 1 site in Turkey (Türkiye).
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 4 inclusion and 5 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: finished, as of the sponsor's last update on 2 Sep 2026. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 1 site in Turkey (Türkiye). Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
Are results available for this study?
The study is completed, but results are not available in the source record. That does not mean the treatment did or did not work.
How can a doctor refer a patient or contact the research team?
The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Time to reach the substrate crossover point (time frame: Time Frame: Baseline (single test session, Day 1)). The study lists 2 primary outcomes in all. It is what the study was designed to measure, not a finding.
Where can I read the original study information?
On the ClinicalTrials.gov record for NCT07799662, which also lists 1 linked publication.
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 2 Sep 2026.