# Timing of Exercise Affects Glycemic Control in Type 2 Diabetes Patients Treated with Metformin

PMID: 29785399
Journal: Journal of diabetes research
Published: 2018
Authors: Huang T, Lu C, Schumann M, Le S, Yang Y, Zhuang H, Lu Q, Liu J, Wiklund P, Cheng S

## Question

Does the timing of a single HIIT session after breakfast and metformin administration affect acute glucose and insulin responses in adults with type 2 diabetes?

## Summary

This randomized crossover study tested one cycling HIIT session at 30, 60, or 90 minutes after breakfast and metformin in adults with type 2 diabetes. All exercise timings lowered glucose immediately after exercise compared with metformin-only control. Exercise at 60 or 90 minutes after breakfast produced larger in-exercise glucose declines than exercise at 30 minutes, while 30- and 60-minute timing produced larger insulin decreases than metformin alone. The study is acute, not a training program.

## Population

- Adults aged 30-65 with type 2 diabetes diagnosed within 5 years and treated with metformin only.
- Sample size: 26
- Age: Mean 53.8 +/- 8.6 years
- Sex: 14 women and 12 men
- Health status: Type 2 diabetes treated with metformin; no major cardiovascular, musculoskeletal, or mental disease.

## Methodology

- Randomized crossover acute exercise trial with four laboratory conditions.
- Four single-day testing conditions separated by at least 48 hours between exercise sessions.
- Clinical/laboratory exercise testing setting in China.
- Randomized and controlled study design.

## Protocol

- Postbreakfast cycling HIIT.
- Modality: Cycle ergometer.
- Work intervals: 1 min at 85% maximal watts.
- Recovery: 3 min at 40% maximal watts.
- Sets or repetitions: 6 bouts.
- Intensity: 85% maximal watts.
- Session duration: 27 min.
- Frequency: Single session at each timing with at least 48 h between exercise sessions.
- Program length: Acute crossover trial.
- Progression: None.
- Metformin-only condition.
- Modality: No exercise.
- Frequency: One laboratory day.
- Program length: Acute condition.

## Outcomes

### Immediate postexercise glucose
Status: improved
All three HIIT timing conditions reduced glucose more than metformin alone immediately after exercise.

EX30 -2.58 mmol/L, EX60 -2.13 mmol/L, EX90 -1.87 mmol/L versus Metf; all p<0.001.

### Glucose during exercise
Status: mixed
Glucose reductions during exercise were larger at 60 and 90 minutes postbreakfast than at 30 minutes.

EX60 and EX90 reductions were significantly larger than EX30, p<0.001.

### Insulin
Status: improved
Compared with metformin alone, insulin decreased more in EX30 and EX60.

Both p<0.001.

### SOD activity
Status: no clear change
Postexercise SOD activity changes did not differ from metformin-only control.

## Practical Insights

- For type 2 diabetes users, HIIT timing relative to breakfast and medication may affect acute glucose changes.
- This paper is useful for medical caveats and content, not generic workout prescription.
- The protocol used only 6 minutes of hard work but 27 minutes total exercise because recoveries were long.

## Limitations

- Acute study only.
- No exercise-only condition.
- Only metformin-treated patients.
- Only postbreakfast exercise was studied.
- Insulin sensitivity and long-term glycemic control were not assessed.

## Safety And Adherence

- The timing window was selected partly because prior evidence suggested minimal hypoglycemia risk.
- No exercise-related adverse-event finding was highlighted.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/29785399/) (pubmed)
- [DOI](https://doi.org/10.1155/2018/2483273) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5896215/) (full text)

## Agent Guidance

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