# The acute physiological and perceptual effects of recovery interval intensity during cycling-based high-intensity interval training

PMID: 33098020
Journal: European Journal of Applied Physiology
Published: 2020-10-23
Authors: Fennell CRJ, Hopker JG

## Question

How does recovery interval intensity affect physiological and perceptual responses during self-paced cycling-based aerobic HIIT?

## Summary

Fourteen trained cyclists completed six randomized lab HIIT sessions: 6 x 4 minutes or 3 x 8 minutes, each with passive recovery, active recovery at 80% lactate-threshold power, or active recovery at 110% lactate-threshold power. Passive recovery let cyclists produce higher work-interval power and spend more time at high percentages of maximal minute power while producing similar oxygen-uptake stress and lower session RPE than the hardest active recovery.

## Population

- Fourteen trained cyclists with at least 2 years competitive racing experience.
- Sample size: 14
- Age: 33 +/- 13 years.
- Fitness level: Trained to professional cyclists; VO2peak 62 +/- 9 mL/kg/min.
- Health status: Healthy status not detailed; all gave informed consent and completed ethically approved testing.

## Methodology

- Randomized repeated-measures crossover laboratory study.
- Seven laboratory visits: one preliminary visit and six acute HIIT sessions on non-concurrent days.
- Exercise physiology laboratory using cyclists' own bikes on a Cyclus2 ergometer.
- Randomized and controlled study design.

## Protocol

- Cycling HIIT with passive or active recovery.
- Modality: Cycling.
- Work intervals: 6 x 4 min or 3 x 8 min self-paced maximal session effort.
- Recovery: Passive seated recovery, active recovery at 80% LT power, or active recovery at 110% LT power.
- Sets or repetitions: 6 intervals for 4 min protocol; 3 intervals for 8 min protocol.
- Intensity: Highest possible work-interval power output; recovery at PA, 80A, or 110A.
- Session duration: About 52-54 min including warm-up, between-interval recoveries, and cooldown.
- Frequency: Six lab sessions on non-concurrent days.
- Program length: Acute crossover study.
- Progression: No progression; randomized protocol order.
- Recovery intensity comparisons.
- Modality: Passive seated recovery or active cycling recovery.
- Work intervals: Same 6 x 4 min or 3 x 8 min work intervals across recovery conditions.
- Recovery: 2 min or 4 min at PA, 80% LT power, or 110% LT power.
- Sets or repetitions: Within-subject crossover across six conditions.
- Intensity: Passive, 80A, or 110A recovery.
- Session duration: Matched work duration of 24 min; total session differed by protocol recovery duration.
- Frequency: Each condition completed once.
- Program length: Acute crossover study.
- Progression: No progression.

## Outcomes

### Work power
Status: improved
Passive recovery increased time above high percentages of MMP and supported higher work-interval power than active recovery.

Time above 80%, 90%, and 95% MMP higher with PA than 80A and 110A during both protocols; all p<=0.001.

### VO2 stress
Status: no clear change
Recovery intensity did not significantly change time above 90% or 95% VO2peak during work intervals.

>90% VO2peak p=0.11; >95% VO2peak p=0.50.

### Session RPE
Status: worse/safety concern
110A active recovery made sessions feel harder than passive or 80A recovery.

6 x 4 sRPE: PA 8.3 +/- 0.7, 80A 8.7 +/- 0.6, 110A 9.1 +/- 0.5; 3 x 8 sRPE: PA 8.6 +/- 0.7, 80A 8.5 +/- 0.6, 110A 9.1 +/- 0.5; p<=0.001.

### Blood lactate
Status: mixed
Active recovery showed lower lactate in the 6 x 4 session, likely because work-interval intensity was lower.

BLa recovery-intensity main effect for 6 x 4 p<0.001; not significant for 3 x 8 p=0.06.

## Practical Insights

- Passive recovery can be a better default between hard long cycling intervals when work quality matters.
- Active recovery above lactate threshold can make a session harder without improving VO2 time at target.
- Recovery intensity should be prescribed and tracked as part of HIIT design.

## Limitations

- Small trained-cyclist sample.
- Acute crossover design only.
- No chronic adaptation outcomes.
- Cycling lab setting limits transfer to bodyweight HIIT.
- Sex distribution was not stated in the extracted NXML.

## Safety And Adherence

- No adverse events were reported.
- Participants were trained cyclists tested under laboratory monitoring.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/33098020/) (pubmed)
- [DOI](https://doi.org/10.1007/s00421-020-04535-x) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7862540/) (full text)

## Agent Guidance

Preserve the paper-level scope of this note. Do not generalize beyond the population, protocol, measured outcomes, and limitations above.