# Conventional methods to prescribe exercise intensity are ineffective for exhaustive interval training

PMID: 36988672
Journal: European journal of applied physiology
Published: 2023-08-01
Authors: Bossi AH, Cole D, Passfield L, Hopker J

## Question

Which relative intensity prescription method best normalizes time to exhaustion, physiological responses, and perceptual responses during exhaustive HIIT?

## Summary

This acute crossover study tested four common ways to set cycling HIIT intensity in trained cyclists. Every participant completed exhaustive 4-minute-on, 2-minute-off HIIT sessions using different prescription methods. The main finding was practical: none of the conventional methods normalized how hard the workouts were between individuals. Time to exhaustion and physiological/perceptual responses varied widely. This matters for workout generation because a percentage-based prescription can still produce very different experiences across users.

## Population

- Recreationally trained competitive cyclists.
- Sample size: 18
- Age: 38 +/- 11 years.
- Sex: 16 male, 2 female.
- Fitness level: Trained cyclists; VO2max 54.3 +/- 8.9 mL/kg/min.
- Health status: Apparently healthy volunteers.

## Methodology

- Randomized acute repeated-measures/crossover laboratory study of four HIIT prescription methods.
- Six lab visits separated by at least 48 hours; acute HIIT sessions to exhaustion.
- Exercise physiology laboratory with trained cyclists.
- Randomized and controlled study design.

## Protocol

- Exhaustive cycling HIIT prescription-method comparison.
- Modality: Cycling.
- Work intervals: 4 minutes.
- Recovery: 2 minutes.
- Sets or repetitions: Until exhaustion or 10 work intervals.
- Intensity: 70% delta, 85% Wmax, 120% 20-minute TT, or 80% W prime.
- Session duration: Variable to exhaustion; median TTE 13.8-26.7 minutes depending condition.
- Frequency: Four experimental sessions across separate visits.
- Program length: Acute crossover study.
- Progression: None.
- Alternative intensity prescription methods.
- Modality: Same cycling HIIT structure.
- Work intervals: 4 minutes.
- Recovery: 2 minutes.
- Sets or repetitions: Until exhaustion or 10 work intervals.
- Intensity: Compared 70% delta, 85% Wmax, 120%TT, and 80%W prime.
- Session duration: Variable to exhaustion.
- Frequency: Separate randomized visits.
- Program length: Acute.
- Progression: None.

## Outcomes

### Interindividual variability
Status: no clear change
All prescription methods showed high interindividual variability with overlapping confidence intervals.

Interindividual CV for TTE ranged from 44.2% for 85% Wmax to 59.1% for 120%TT.

### Time to exhaustion
Status: mixed
70% delta produced longer median TTE than 120%TT and 80%W prime, but did not solve variability.

Median TTE: 26.7 min for 70% delta, 17.4 min for 85% Wmax, 13.8 min for 120%TT, 14.2 min for 80%W prime.

### Prescription method validity
Status: no clear change
No method was clearly superior for normalizing performance, physiological, or perceptual acute responses.

Authors report substantial overlap in confidence intervals across dependent variables.

## Practical Insights

- Intensity prescription needs feedback and adjustment; percentages alone are not enough.
- Time to exhaustion can vary dramatically even among trained users.
- User-facing HIIT should include RPE/completion feedback loops to personalize load.
- Exhaustive protocols are useful for research but not a default consumer format.

## Limitations

- Small sample.
- Trained cyclist sample.
- Acute-only study.
- Laboratory prescription methods not available to typical consumers.
- 70% delta condition was lower in absolute/relative watts than other conditions.

## Safety And Adherence

- Exhaustive sessions were stopped at exhaustion or after 10 work intervals.
- Adverse event details were not extracted from visible text.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/36988672/) (pubmed)
- [DOI](https://doi.org/10.1007/s00421-023-05176-6) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10363074/) (full text)

## Agent Guidance

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