# Reduced-exertion high-intensity interval training improves the fitness-fatness index in physically inactive adults

PMID: 35992158
Journal: Frontiers in Sports and Active Living
Published: 2022
Authors: Leahy DJ, Dalleck LC, Ramos JS

## Question

Does 8 weeks of reduced-exertion HIIT improve the fitness-fatness index more than moderate-intensity continuous training in physically inactive adults?

## Summary

In inactive low-to-moderate-risk adults, 8 weeks of very short REHIT cycling improved the fitness-fatness index more than a longer moderate-intensity program. REHIT required only two 20-second sprints in a 10-minute session but used a specialized cycle ergometer and had more dropouts than the MICT group.

## Population

- Physically inactive university and hospital staff at low-to-moderate ACSM risk.
- Sample size: 32
- Age: Completers: REHIT 40.8 +/- 10.8 years; MICT 42.9 +/- 9.7 years
- Sex: Completers included 5 male in REHIT and 6 male in MICT
- Fitness level: Physically inactive
- Health status: Low-to-moderate risk; excluded metabolic, cardiovascular, and pulmonary disease

## Methodology

- Randomized two-arm supervised exercise intervention
- 8 weeks
- Workplace/university-hospital exercise setting using CAR.O.L bike for REHIT
- Randomized and controlled study design.

## Protocol

- REHIT.
- Modality: Specialized CAR.O.L cycle ergometer.
- Work intervals: 20 seconds.
- Recovery: 3 minutes between sprints.
- Sets or repetitions: 2 sprints per session.
- Intensity: All-out sprint efforts with machine-adjusted resistance.
- Session duration: 10 minutes.
- Frequency: 2 days/week weeks 1-2, 3 days/week weeks 3-4, 4 days/week weeks 5-8.
- Program length: 8 weeks.
- Progression: Frequency progressed from 2 to 4 sessions per week.
- MICT.
- Modality: Aerobic exercise.
- Work intervals: Continuous exercise.
- Recovery: Not applicable.
- Sets or repetitions: 25-30 minute continuous sessions.
- Intensity: 40-65% heart-rate reserve, progressing by week.
- Session duration: 25-30 minutes.
- Frequency: 3-5 days per week.
- Program length: 8 weeks.
- Progression: Progressed from 40-50% HRR for 3 days/week to 60-65% HRR for 5 days/week.

## Outcomes

### FFI
Status: improved
Both groups improved FFI, with a larger improvement after REHIT.

REHIT 14.65 to 16.60; MICT 14.84 to 15.82; both p<0.001; change REHIT 1.95 +/- 0.63 vs MICT 0.99 +/- 0.47, p<0.001.

### FFI responders
Status: improved
All REHIT completers were FFI responders compared with about half of MICT completers.

REHIT 12/12 vs MICT 8/15 improved FFI by at least 1 point, p=0.01.

### VO2max
Status: improved
VO2max increased in both groups.

REHIT 25.3 to 28.4 mL/kg/min; MICT 26.2 to 28.0 mL/kg/min.

### Adherence
Status: mixed
Session adherence was high among completers, but REHIT had more withdrawals.

Adherence REHIT 89.2% and MICT 87.8%; dropouts REHIT 4/16 and MICT 1/16.

## Practical Insights

- Two 20-second all-out cycling sprints in a 10-minute session can improve a combined fitness-fatness metric in inactive adults.
- The protocol is time-efficient but depends on a specialized bike that automatically adjusts resistance.
- Dropout/tolerability should be monitored because more participants withdrew from REHIT than MICT.

## Limitations

- Small completed sample.
- No no-exercise control group.
- Diet and outside physical activity/sedentary behavior were not tightly controlled.
- REHIT had more dropouts.
- Commercial specialized bike limits direct replication.

## Safety And Adherence

- No adverse events were reported.
- Five randomized participants dropped out: REHIT illness n=3 and personal n=1; MICT illness n=1.
- Participants were screened as low-to-moderate risk and without metabolic, cardiovascular, or pulmonary disease.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/35992158/) (pubmed)
- [DOI](https://doi.org/10.3389/fspor.2022.961957) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9388827/) (full text)

## Agent Guidance

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