# Effects of High-Intensity Interval Training and Isoinertial Training on Leg Extensors Muscle Function, Structure, and Intermuscular Adipose Tissue in Older Adults

PMID: 31649552
Journal: Frontiers in Physiology
Published: 2019-10-09
Authors: Bruseghini P, Capelli C, Calabria E, Rossi AP, Tam E

## Question

How do aerobic HIT and isoinertial resistance training affect quadriceps muscle function, size, architecture, activation, and intermuscular adipose tissue in healthy older men?

## Summary

In 12 healthy older men, 8 weeks of supervised cycling HIT increased quadriceps muscle cross-sectional area, volume, pennation angle, and reduced intermuscular adipose tissue, but did not significantly improve maximal knee-extension torque. A later flywheel resistance block improved strength more clearly. The design had no separate control group.

## Population

- Moderately active healthy older Caucasian men.
- Sample size: 12
- Age: 69.3 +/- 4.2 years; range 65-75
- Sex: Men only
- Fitness level: Moderately active
- Health status: Healthy after medical screening.

## Methodology

- Within-subject sequential intervention study comparing HIT followed after detraining by isoinertial resistance training.
- 8 weeks HIT, 12 weeks recovery/detraining, then 8 weeks IRT
- Supervised laboratory/training setting in Verona, Italy.

## Protocol

- Cycling HIT.
- Modality: Cycle ergometer.
- Work intervals: 2 min.
- Recovery: 2 min at about 40% VO2max.
- Sets or repetitions: 7 bouts.
- Intensity: 85-95% VO2max.
- Session duration: 45-50 min.
- Frequency: 3 sessions/week.
- Program length: 8 weeks.
- Progression: Workload adjusted every 14 days based on HR/workload relationship.
- Isoinertial resistance training.
- Modality: Seated knee-extension flywheel ergometer.
- Work intervals: Maximal concentric-eccentric actions.
- Recovery: 3 min between sets.
- Sets or repetitions: 4 sets of 7 maximal actions.
- Intensity: Maximal effort with verbal encouragement and force feedback.
- Session duration: About 30 min.
- Frequency: 3 sessions/week.
- Program length: 8 weeks after 12 weeks recovery.
- Progression: Workload adapted by increasing maximum force across sessions.

## Outcomes

### Quadriceps volume and ACSA
Status: improved
HIT and IRT both increased quadriceps ACSA and volume.

Volume HIT +42.2 cm3 p=0.003; IRT +68.2 cm3 p=0.001; ACSA increased at 25%, 50%, and 75% femur length.

### IMAT
Status: improved
IMAT at 50% femur length decreased after HIT and IRT.

HIT p=0.001; IRT p=0.003.

### Strength
Status: mixed
Knee-extensor torque significantly increased only after IRT, not after HIT.

IRT T_MVC +11.5 Nm p=0.040; T_C +8.8 Nm p=0.008.

### Activation and PCSA
Status: mixed
Pennation angle increased after both; PCSA and voluntary activation significantly increased only after IRT.

Activation p=0.011 after IRT; PCSA p=0.025 after IRT.

## Practical Insights

- Cardio-machine HIIT may improve muscle quality without producing task-specific strength gains.
- Older-adult strength goals likely need resistance training in addition to HIIT.
- Small uncontrolled mechanistic studies should inform hypotheses, not user-facing efficacy claims alone.

## Limitations

- No control group
- Not randomized
- Not counterbalanced
- Small male-only sample
- Healthy screened volunteers only

## Safety And Adherence

- No injuries or health disorders were reported.
- All sessions were supervised and participants were medically screened.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/31649552/) (pubmed)
- [DOI](https://doi.org/10.3389/fphys.2019.01260) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6794371/) (full text)

## Agent Guidance

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