What is the clinical evidence from this study?

Study design: RCT. Population: Healthy physically active males (n=8). Intervention: Steady-state aerobic exercise vs. 15 min vs 45 min duration. Primary outcome: Difference between %HRR and %VO2R during 45-min steady-state exercise (MD 6.7 percentage points, p=0.009).

April 25, 2022Open Access

Effect of steady-state aerobic exercise intensity and duration on the relationship between reserves of heart rate and oxygen uptake

Key Result

Steady-state exercise duration significantly affects the %HRR-%VO2R relationship, with %HRR being 6.7 percentage points higher than %VO2R during 45-minute exercises.

Study Design

Type

RCT (n=8)

Blinding

Open-label

Randomization

Block randomization

Multicenter

Structured PICO

Does steady-state exercise duration and intensity affect the 1:1 relationship between heart rate reserve and oxygen uptake reserve in physically active males?

Population

8 physically active males, mean age 22.6 ± 1.2 years.

Intervention

Steady-state exercise (running) at varying randomly assigned durations (15 min, 45 min) and intensities (60% HRR, 80% HRR).

Comparator

Within-subject comparison across different exercise durations and intensities.

Outcome

Difference between percentages of heart rate reserve (%HRR) and oxygen uptake reserve (%V̇O2R) during the last 5 min of steady-state exercise.surrogate

The assumed 1:1 relationship between heart rate reserve and oxygen uptake reserve for exercise prescription is not valid for longer duration (45-min) steady-state exercise, where %HRR overestimates %V̇O2R.

Main Result

Effect estimate: MD 6.7 percentage points

p-value: p=0.009

Limitations

Small sample size
Homogeneity of participants (all physically active males)
Pre-exercise HR and VO2 were not measured during the SSE sessions
Warm-up speed was estimated using the ACSM running equation rather than measured
Site-specific technical error of the dependent variables was not assessed
Exercise intensity domains were not considered

Abstract

Background The percentages of heart rate (%HRR) or oxygen uptake (%V̇O 2 R) reserve are used interchangeably for prescribing aerobic exercise intensity due to their assumed 1:1 relationship, although its validity is debated. This study aimed to assess if %HRR and %V̇O 2 R show a 1:1 relationship during steady-state exercise (SSE) and if exercise intensity and duration affect their relationship. Methods Eight physically active males (age 22.6 ± 1.2 years) were enrolled. Pre-exercise and maximal HR and V̇O 2 were assessed on the first day. In the following 4 days, different SSEs were performed (running) combining the following randomly assigned durations and intensities: 15 min, 45 min, 60% HRR, 80% HRR. Post-exercise maximal HR and V̇O 2 were assessed after each SSE. Using pre-exercise and post-exercise maximal values, the average HR and V̇O 2 of the last 5 min of each SSE were converted into percentages of the reserves (%RES), which were computed in a 3-way RM-ANOVA ( α = 0.05) to assess if they were affected by the prescription parameter (HRR or V̇O 2 R), exercise intensity (60% or 80% HRR), and duration (15 or 45 min). Results The %RES values were not affected by the prescription parameter ( p = 0.056) or its interactions with intensity ( p = 0.319) or duration and intensity ( p = 0.117), while parameter and duration interaction was significant ( p = 0.009). %HRRs and %V̇O 2 Rs did not differ in the 15-min SSEs (mean difference MD = 0.7 percentage points, p = 0.717), whereas %HRR was higher than %V̇O 2 R in the 45-min SSEs (MD = 6.7 percentage points, p = 0.009). Conclusion SSE duration affects the %HRR-%V̇O 2 R relationship, with %HRRs higher than %V̇O 2 Rs in SSEs of longer duration.

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