# Very Low Volume High-Intensity Interval Exercise Is More Effective in Young Than Old Women

PMID: 29854804
Journal: BioMed Research International
Published: 2018-05-09
Authors: Krusnauskas R, Venckunas T, Snieckus A, Eimantas N, Baranauskiene N, Skurvydas A, Brazaitis M, Liubinskiene A, Kamandulis S

## Question

How do young and older women differ in acute neuromuscular, metabolic, cytokine, and perceptual responses to three very low-volume HIIT cycling session formats?

## Summary

Young and older women completed three acute cycling interval sessions in randomized order. Six 5-second all-out sprints were the most preferred and produced physiological stress, especially in young women, while older women appeared to need longer bouts for comparable stress. This was an acute mechanistic/tolerability study, not a training trial.

## Population

- Young and older women who passed medical screening and procedure familiarization.
- Sample size: 19
- Age: Young 19.5 +/- 1.3 years; older 65.7 +/- 2.8 years.
- Sex: Women only.
- Fitness level: Recreationally active 1-2 times per week; both groups reported more than 3000 MET-min/week on average.
- Health status: Medically screened; excluded for cardiovascular complaint, metabolic disease sign, chronic joint pain, or poor compliance with procedures.

## Methodology

- Acute randomized crossover comparison of three cycling interval session types, separated by 5-week washout periods.
- Three acute sessions, each separated by 5 weeks.
- Laboratory cycling and neuromuscular testing at Lithuanian Sports University.
- Randomized and controlled study design.

## Protocol

- Very-low-volume acute cycling HIIT comparison.
- Modality: Mechanically braked cycle ergometer.
- Work intervals: 6 x 5 seconds all-out, 3 x 30 seconds all-out, or 3 x 60 seconds submaximal.
- Recovery: 90 seconds between 5-second sprints; 4 minutes between 30- or 60-second bouts; minimal-resistance cycling during rest.
- Sets or repetitions: Each participant completed all three session types in randomized order.
- Intensity: All-out at 7.5% body weight for 5- and 30-second bouts; submaximal at 3.75% body weight for 60-second bouts.
- Session duration: 7-8 minute warm-up plus the assigned interval session.
- Frequency: Single exposure to each session type, separated by 5 weeks.
- Program length: Acute crossover study, not a training program.
- Progression: No progression; randomized session order with washout.
- Alternative HIIT session formats within crossover.
- Modality: Same cycle ergometer.
- Work intervals: Comparison among 6 x 5 seconds, 3 x 30 seconds, and 3 x 60 seconds.
- Recovery: Protocol-specific rest periods.
- Sets or repetitions: Within-person comparison.
- Intensity: All-out and submaximal cycling loads.
- Session duration: Acute sessions.
- Frequency: One session of each type.
- Program length: Acute.
- Progression: Randomized order; no training progression.

## Outcomes

### Power and metabolic stress
Status: mixed
Young women produced higher power and lactate responses than older women; 6 x 5 seconds produced the highest power but lower HR/RPE than longer bouts.

Peak and average power were higher in young than older women and highest in 6 x 5 seconds; p < 0.05. Lactate was higher in young women after all sessions.

### Low-frequency fatigue
Status: mixed
All protocols caused fatigue signals, but the 3 x 30 and 3 x 60 second sessions produced greater low-frequency fatigue than 6 x 5 seconds; responses were larger in young women.

P20/P100 decline was more evident after 3 x 30 and 3 x 60 seconds than after 6 x 5 seconds and larger in young women; p < 0.05.

### Preference
Status: improved
Both age groups preferred the 6 x 5 second session for future training.

90% of all participants ranked 6 x 5 seconds as most preferred; p < 0.05.

### TNF-alpha and IGF-1
Status: no clear change
TNF-alpha did not change consistently, and IGF-1 changes were minor and non-significant.

No interaction for TNF-alpha by time/session type; IGF-1 changes after exercise were minor, p > 0.05.

## Practical Insights

- Ultra-short all-out intervals may be more acceptable, but older adults may not generate enough intensity in 5 seconds to achieve the same stimulus.
- Preference and physiological stimulus can diverge: the most preferred protocol may not be the strongest training stimulus for all age groups.
- Acute fatigue persisting to 24 hours in some protocols matters for recovery scheduling.

## Limitations

- Acute study, not a training intervention.
- Small sample with women only.
- Session work was not matched, limiting isolation of intensity effects.
- Maximal power measured in 5-second intervals may have overestimated relative intensity for older women.
- Large variability in cytokine responses.
- Laboratory cycling and electrical stimulation outcomes are not directly user-facing.

## Safety And Adherence

- Participants were medically screened and familiarized; only compliant participants were recruited.
- The introduction notes potential dizziness/collapse with all-out efforts, but the results did not report adverse events from the study sessions.
- Authors concluded longer sessions were psychologically tolerable in older women.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/29854804/) (pubmed)
- [DOI](https://doi.org/10.1155/2018/8913187) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5966693/) (full text)

## Agent Guidance

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