# Initial Dietary Protein Intake Influence Muscle Function Adaptations in Older Men and Women Following High-Intensity Interval Training Combined with Citrulline

PMID: 31336654
Journal: Nutrients
Published: 2019 Jul 22
Authors: Buckinx F, Marcangeli V, Pinheiro Carvalho L, Dulac M, Hajj Boutros G, Gouspillou G, Gaudreau P, Morais J, Noirez P, Aubertin-Leheudre M

## Question

Does baseline dietary protein intake modify the effects of citrulline plus HIIT or placebo plus HIIT on body composition, muscle strength, power, and functional capacity in obese older adults?

## Summary

This a posteriori analysis used completers from a 12-week supervised elliptical HIIT trial in obese older adults who also received blinded citrulline or placebo. All groups improved body composition, strength, power, and functional outcomes, and citrulline appeared most helpful among participants with lower baseline protein intake, but the analysis cannot isolate HIIT alone because everyone trained.

## Population

- Sedentary obese older men and women who completed the HIIT plus citrulline/placebo trial.
- Sample size: 73
- Age: 60 years and older
- Sex: Men and women
- Fitness level: Inactive during prior 6 months (<2 h/week structured exercise)
- Health status: Obese by fat mass thresholds; no orthopedic limitations, contraindication to physical activity, major neurological/cardiovascular/lung disease, or cognitive disorder

## Methodology

- A posteriori subgroup analysis of a double-blind randomized controlled supplementation trial where all groups completed HIIT
- 12 weeks
- University of Quebec at Montreal physical activity sciences department
- Randomized and controlled study design.

## Protocol

- Elliptical HIIT plus citrulline.
- Modality: Elliptical trainer.
- Work intervals: 30 seconds.
- Recovery: 90 seconds moderate intensity.
- Sets or repetitions: Multiple intervals across 20 min.
- Intensity: 80-85% MHR or Borg >17 during high intervals.
- Session duration: 30 minutes.
- Frequency: 3 sessions/week.
- Program length: 12 weeks.
- Progression: Speed/resistance adjusted during sessions to keep HR above 80% during high-intensity intervals.
- Elliptical HIIT plus placebo.
- Modality: Elliptical trainer.
- Work intervals: 30 seconds.
- Recovery: 90 seconds moderate intensity.
- Sets or repetitions: Multiple intervals across 20 min.
- Intensity: 80-85% MHR or Borg >17 during high intervals.
- Session duration: 30 minutes.
- Frequency: 3 sessions/week.
- Program length: 12 weeks.
- Progression: Same HIIT protocol as citrulline groups.

## Outcomes

### Overall parameters
Status: improved
All four HIIT plus supplement/placebo/protein-intake groups improved the measured parameters.

Article reports four groups improved significantly regarding all measured parameters.

### Gynoid fat
Status: improved
CIT-PROT- decreased gynoid fat more than PLA-PROT- and CIT-PROT+.

p=0.04 versus PLA-PROT-; p=0.02 versus CIT-PROT+.

### Strength
Status: mixed
CIT-PROT+ improved knee extensor strength more than PLA-PROT+, while CIT-PROT- improved relative handgrip more than CIT-PROT+.

KESr p=0.04; HSr p=0.02.

### Protein intake
Status: mixed
Baseline protein intake appeared relevant in citrulline groups but not placebo groups.

No significant placebo-group differences by protein intake.

## Practical Insights

- Low-impact elliptical HIIT may be a useful format for obese older adults.
- Protein intake can be a relevant context variable when evaluating supplement plus exercise outcomes.
- Do not use this analysis to claim HIIT alone caused the between-group differences.

## Limitations

- A posteriori subgroup analysis
- Small subgroups
- No no-exercise or citrulline-only control
- Protein intake not randomized or controlled
- Actual attendance/adherence rate not fully reported beyond >=80% inclusion threshold and exclusions

## Safety And Adherence

- Article did not report adverse events or injuries.
- Safety context included PAR-Q/no contraindication screening, no orthopedic limitations, major neurological/cardiovascular/lung/cognitive disease exclusions, low-impact elliptical HIIT, and kinesiologist-supervised HR/RPE monitoring.
- Out of 107 eligible parent-trial participants, 83 completed the 12-week HIIT intervention; 9 refused, 15 were excluded for adherence <80%, and 10 completers were later excluded from this analysis for incomplete food data.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/31336654/) (pubmed)
- [DOI](https://doi.org/10.3390/nu11071685) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6683270/) (full text)

## Agent Guidance

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