Aerobic Interval vs Continuous Training on Heart Rate-Power Decoupling in Ischemic Heart Disease

March 16, 2026 updated by: Isidro Fernández López, Universidad Complutense de Madrid

Effects of Long Extensive Aerobic Interval Training Versus Long Extensive Continuous Training on Heart Rate-Power Decoupling in Patients With Ischemic Heart Disease: A Randomized Clinical Trial

This study is a randomized, parallel-group clinical trial with assessor and statistical analyst blinding, conducted at a single center. Participants with stable ischemic heart disease enrolled in a cardiac rehabilitation program will be randomly allocated to one of two aerobic exercise interventions: long extensive continuous aerobic training (zone 2) or long extensive aerobic interval training (zone 3). Both groups will participate in supervised exercise sessions twice weekly for a period of 8 weeks, integrated into the standard cardiac rehabilitation program.

Assessments will be performed at baseline, immediately after the intervention period (8 weeks), and after a 4-week follow-up period without supervised training to evaluate potential detraining effects. The primary outcome is heart rate-power decoupling during a prolonged submaximal cycling exercise test, used as an indicator of cardiovascular efficiency. Secondary outcomes include heart rate response during submaximal exercise, exercise tolerance, heart rate recovery, blood pressure, functional capacity, quality of life, and adherence to the training program.

The objective of this study is to compare the effects of long extensive aerobic interval training versus long extensive continuous training on heart rate-power decoupling and related cardiovascular and functional outcomes in patients with ischemic heart disease undergoing cardiac rehabilitation.

Study Overview

Status

Not yet recruiting

Conditions

Intervention / Treatment

Detailed Description

BACKGROUND AND RATIONALE Cardiac rehabilitation (CR) based on supervised aerobic exercise is a well-established intervention that reduces cardiovascular morbidity and mortality, improves functional capacity, and enhances quality of life in patients with ischemic heart disease. Two aerobic training modalities are routinely used within CR programs and recommended by international guidelines: moderate-intensity continuous training (MICT, zone 2), characterized by prolonged steady-state exercise below the first ventilatory threshold (65-75% HRmax); and long extensive interval training (LEIT, zone 3), which alternates prolonged work intervals between the two ventilatory thresholds (75-85% HRmax) with active recovery periods. Both modalities are standard components of the Phase II CR program at Hospital Universitario 12 de Octubre (HU12O), Madrid, where this trial is conducted.

Despite the established benefits of both training modalities, no randomized controlled trial has directly compared their effects on heart rate-power decoupling during submaximal exercise - a physiological marker of cardiovascular efficiency that remains underexplored in the CR setting.

HEART RATE-POWER DECOUPLING: PHYSIOLOGICAL BASIS During constant-load cycling exercise, an efficient cardiovascular system maintains a relatively stable heart rate (HR) over time. When HR progressively increases despite unchanged mechanical power output, this phenomenon - termed HR-power decoupling or cardiovascular drift - reflects a declining stroke volume compensated by chronotropic response, resulting in greater cardiac work per unit of mechanical output. A higher decoupling index indicates lower cardiorespiratory efficiency during submaximal exercise.

HR-power decoupling can be assessed using standard CR equipment (calibrated cycle ergometer and validated chest-strap HR monitor), without maximal testing or specialized technology, making it a clinically applicable and safe measure in this population. Reducing HR-power decoupling after training would indicate that the heart operates with lower hemodynamic load for the same mechanical demand - a meaningful adaptation in terms of myocardial oxygen consumption, exercise tolerance, and long-term cardiovascular prognosis.

STUDY DESIGN RATIONALE A parallel-group design was chosen over a crossover design to avoid carry-over effects, as aerobic training adaptations may persist for weeks after program completion. Assessor and statistical analyst blinding is implemented to minimize detection and analysis bias; blinding of the treating physiotherapist is not feasible given the nature of the intervention.

A detraining follow-up assessment at week 12 (4 weeks after supervised training ends) is included to evaluate the durability of adaptations and whether potential between-group differences in central versus peripheral cardiovascular adaptations result in differential rates of detraining.

INTERVENTIONS

All participants follow the standard HU12O CR protocol, which includes an identical resistance and mobility training block (35-40 min, <50% 1RM) and warm-up and cool-down phases in every session. The sole differential component is the aerobic training block (approximately 40 min of active aerobic exercise):

  • Continuous training group (Zone 2): 40 minutes of continuous cycling at 65-75% of individual HRmax, maintained at steady state. Target HR range is determined individually from the baseline incremental test and adjusted weekly to account for training-induced adaptations.
  • Interval training group (Zone 3): 8 work intervals of 3 minutes at 75-85% HRmax, each followed by 2 minutes of active recovery below 65-70% HRmax (total block: 40 min), equating total training volume to the continuous group. Work intensity targets the zone between the two ventilatory thresholds.

Intensity is controlled by dual monitoring of HR and rating of perceived exertion (Borg scale 6-20; target RPE 11-13 for zone 2 and 13-16 for zone 3). In participants with blunted chronotropic response (e.g., beta-blocker therapy), RPE serves as the primary intensity reference. Power output (watts) is progressively adjusted across sessions to maintain target HR ranges as cardiorespiratory fitness improves.

PRIMARY OUTCOME ASSESSMENT The HR-power decoupling index is assessed via a 20-minute constant-load submaximal cycling test at an individualized fixed power output. HR is recorded continuously via validated chest-strap sensor. The decoupling index is calculated as the relative percentage change in mean HR between the first third (minutes 0-6) and the last third (minutes 14-20) of the test: [(HR₁₄-₂₀ - HR₀-₆) / HR₀-₆] × 100. Higher values indicate greater cardiovascular drift and lower efficiency. The minimal clinically important difference (MCID) is set at 0.12 units. Immediately following the 20-minute test, a 5-minute passive recovery period is used to assess post-exercise HR recovery (HRR₁, HRR₂, HRR₅).

SAMPLE SIZE Sample size was calculated using G*Power 3.1.9.7 for a two-factor repeated-measures ANOVA (2 groups × 3 time points), with 80% power, α = 0.05, correlation between repeated measures of 0.50, and an expected effect size of f = 0.51 (Cohen d = 0.83; MCID = 0.15 units; SD ≈ 0.18). This yielded a minimum of 34 participants. Accounting for an estimated 15% dropout rate, the target sample is 40 participants (20 per group).

STATISTICAL ANALYSIS The primary analysis will use a two-way repeated-measures ANOVA (group × time), with the group × time interaction as the primary estimator. If sphericity is violated, the Greenhouse-Geisser correction will be applied. If data are not missing completely at random, linear mixed-effects models will be used. The primary analysis follows the intention-to-treat principle; a per-protocol sensitivity analysis will include participants who completed ≥80% of sessions and all three assessments. Missing data will be handled by multiple imputation. Effect sizes will be reported as partial eta-squared (η²p) for ANOVA and Cohen's d for pairwise comparisons. Statistical significance is set at p < 0.05 (two-tailed), with 95% confidence intervals.

ETHICS The protocol has been submitted for approval to the Ethics Committee for Research with Medicinal Products (CEIm) of Hospital Universitario 12 de Octubre. The study will be conducted in accordance with the Declaration of Helsinki and applicable Spanish biomedical research legislation. All participants will provide written informed consent prior to enrollment.

Study Type

Interventional

Enrollment (Estimated)

48

Phase

  • Not Applicable

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Contact

  • Name: Isidro Fernández-López, PhD
  • Phone Number: +34625598970
  • Email: isidrofe@ucm.es

Study Contact Backup

  • Name: Alberto Martos-Monedero, PT

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

  • Adult
  • Older Adult

Accepts Healthy Volunteers

No

Description

Inclusion Criteria:

  • Confirmed diagnosis of cardiovascular disease requiring cardiac rehabilitation, with medical indication for a supervised exercise training program.

  • Prognostic risk classified as low or moderate according to the clinical risk stratification established in the unit, considering:

    • Killip class I or II (absence or mild heart failure)¹.
    • Absence of recent acute myocardial infarction (< 1 month) or presence of a stable previous infarction.
    • Stable and well-controlled cardiovascular symptoms.
    • Physical capacity demonstrated in functional tests ≥ 5 METs, preferably > 7 METs for low-risk patients.
  • Age between 40 and 75 years.
  • Ability to perform physical exercise without absolute contraindications.
  • Written informed consent and willingness to attend the scheduled sessions twice per week for 8 weeks.

Exclusion Criteria:

  • High prognostic risk, defined by:

    • Killip class > III (moderate to severe heart failure).
    • Recent acute myocardial infarction (< 1 month) with clinical instability.
    • Active anginal symptoms or decompensated heart failure.
    • Physical capacity < 5 METs on functional testing, indicating severely reduced exercise capacity.
  • Presence of complex or unstable arrhythmias contraindicating vigorous physical exercise.
  • Concomitant diseases that may limit participation or compromise safety (e.g., advanced pulmonary disease, severe renal failure, severe neuromuscular disorders).
  • Absolute medical contraindications to maximal strength or interval training (e.g., aortic aneurysm, uncontrolled hypertension).
  • Participation in another clinical trial or concurrent rehabilitation program.
  • Inability to comply with attendance requirements or to follow the intervention protocol.

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Treatment
  • Allocation: Randomized
  • Interventional Model: Parallel Assignment
  • Masking: Double

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Active Comparator: Control Group: Extensive Continuous Training

Participants assigned to this arm will undergo an 8-week continuous aerobic training program on a cycle ergometer, with two supervised 90-minute sessions per week.

Each session includes:

Warm-up (10-15 minutes) consisting of low-intensity pedaling (≤60% max HR) and joint mobility exercises.

Main training block: 40 minutes of continuous cycling at moderate intensity (65-75% max HR), individually adjusted based on baseline assessment.

Cool-down (5-10 minutes) with light pedaling and gentle stretching. Additionally, all participants will complete a standardized strength-resistance and mobility training program supervised by specialized physiotherapists, identical for both groups, including controlled exercises with bodyweight and light resistance.
Other: Control Group (A):

Participants will complete an 8-week continuous aerobic training program on a cycle ergometer, with two weekly supervised 90-minute sessions, including:

Warm-up: 10-15 minutes of low-intensity continuous pedaling (≤60% max HR) and joint mobility exercises.

Main aerobic continuous training: 40 minutes of continuous pedaling at 65-75% of maximum heart rate.

Cool-down: 5-10 minutes of light pedaling and stretching.

Monitoring and safety procedures as in the intervention group.
Experimental: Long Extensive Interval Training

Participants assigned to this arm will complete an 8-week aerobic interval training program on a cycle ergometer, with two supervised 90-minute sessions weekly.

Each session includes:

Warm-up (10-15 minutes) of low-intensity pedaling (≤60% max HR) and joint mobility exercises.

Main training block: 8 intervals of 3 minutes at high subthreshold intensity (75-85% max HR), alternating with 2 minutes of active recovery at low-to-moderate intensity (65-70% max HR), totaling approximately 40 minutes.

Cool-down (5-10 minutes) with light pedaling and stretching. As in the other group, all participants will engage in a standardized strength-resistance and mobility program identical across groups.
Other: Intervention Group

Participants will undergo an 8-week aerobic interval training program on a cycle ergometer, consisting of two weekly supervised sessions of 90 minutes. Each session includes:

Warm-up: 10-15 minutes of low-intensity continuous pedaling (≤60% max HR) and joint mobility exercises.

Main aerobic interval training: 8 intervals of 3 minutes pedaling at 75-85% of maximum heart rate, each followed by 2 minutes of active recovery at 65-70% max HR. Total aerobic training duration approximately 40 minutes.

Cool-down: 5-10 minutes of light pedaling and stretching.

Heart rate, blood pressure, and oxygen saturation will be continuously monitored. Safety criteria for session interruption will be applied.

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Change in heart rate-power slope during a submaximal incremental cycling test
Time Frame: Baseline (Week 0), Post-intervention (Week 8), and Follow-up (Week 12)

The heart rate-power slope will be assessed during a submaximal incremental cycling test performed on a cycle ergometer. The protocol will start at 20 W, with workload increases of 10 W every 2 minutes until submaximal termination criteria are reached. Heart rate will be continuously monitored using a validated chest strap device.

The heart rate-power slope will be calculated as:

(Heart rate_initial - Heart rate_final) / (Power_initial - Power_final)

The result will be expressed in beats per minute per watt (bpm/W). Higher values indicate reduced cardiovascular efficiency.
Baseline (Week 0), Post-intervention (Week 8), and Follow-up (Week 12)

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Universidad Complutense de Madrid

Investigators

  • Study Director: Gustavo Plaza-Manzano, PhD, Faculty of Nursing, Physiotherapy and Podiatry. Universidad Complutense de Madrid

Publications and helpful links

The person responsible for entering information about the study voluntarily provides these publications. These may be about anything related to the study.

General Publications

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Estimated)

March 17, 2026

Primary Completion (Estimated)

May 17, 2026

Study Completion (Estimated)

July 3, 2026

Study Registration Dates

First Submitted

March 16, 2026

First Submitted That Met QC Criteria

March 16, 2026

First Posted (Actual)

March 20, 2026

Study Record Updates

Last Update Posted (Actual)

March 20, 2026

Last Update Submitted That Met QC Criteria

March 16, 2026

Last Verified

March 1, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • Interval training cardio
  • TFM-UCM-RC-2026 (Other Identifier: Universidad Complutense de Madrid)

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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