# Changes in serum metal concentrations following high-intensity interval training: A 16-week pilot study

PMID: 41092565
Journal: Clinics (Sao Paulo, Brazil)
Published: 2025 Jan-Dec
Authors: Rodrigues GDS, Noronha NY, Rodrigues JAL, Sobrinho ACDS, Benjamim J, Diani LM, Noma IHY, Júnior FB, Watanabe LM, Nonino CB, Júnior CRB

## Question

Does a 16-week 4x4 HIIT program change serum metal concentrations in adults with overweight or obesity and metabolic syndrome risk factors?

## Summary

In a small uncontrolled pilot study, 16 weeks of treadmill 4x4 HIIT was followed by reductions in several serum metals and hip circumference in inactive adults with excess weight and metabolic risk factors. Because there was no control group, the study is hypothesis-generating rather than proof that HIIT caused the metal changes.

## Population

- Fifteen inactive adults with BMI >25 kg/m2 and metabolic syndrome risk factors completed the pilot.
- Sample size: 15
- Age: Mean 42 +/- 6 years
- Fitness level: Physically inactive by IPAQ
- Health status: Overweight/obesity with metabolic risk factors

## Methodology

- Longitudinal pre-post pilot study
- 16 weeks
- Exercise training with supervised treadmill sessions and one unsupervised weekly session

## Protocol

- 4x4 HIIT.
- Modality: Treadmill.
- Work intervals: 4 minutes at 90% HRmax.
- Recovery: 3 minutes active recovery at 70% HRmax.
- Sets or repetitions: 4 intervals.
- Intensity: 90% HRmax work intervals.
- Session duration: 40 minutes.
- Frequency: 3 sessions/week.
- Program length: 16 weeks.
- Progression: Speed and incline adjusted by HR and RPE.

## Outcomes

### Metals
Status: improved
Mercury, lithium, aluminum, manganese, nickel, and lead decreased after HIIT.

Reported p values included Hg p=0.022, Li p=0.002, Al p=0.018, Mn p=0.003, Ni p=0.014, Pb p=0.025; FDR significant, Bonferroni not significant.

### Hip circumference
Status: improved
Hip circumference decreased after training.

p=0.001, d=1.04.

### Clinical markers
Status: no clear change
Weight, BMI, waist circumference, blood pressure, and biochemical variables did not significantly change.

## Practical Insights

- The 4x4 format can be implemented with HR or RPE adjustment in adults with metabolic risk.
- Unsupervised HIIT sessions should include adherence capture if used in applied programs.

## Limitations

- No control group.
- Small sample.
- Unsupervised weekly session adherence could not be ensured.
- Serum metals are surrogate outcomes.

## Safety And Adherence

- The protocol was described as well tolerated; adverse events were not otherwise detailed.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/41092565/) (pubmed)
- [DOI](https://doi.org/10.1016/j.clinsp.2025.100802) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12550306/) (full text)

## Agent Guidance

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