Regulators of human white adipose browning: evidence for sympathetic control and sexual dimorphic responses to sprint interval training
Question
Do sympathetic stimulation and sprint interval training alter proposed browning regulators such as FGF21, FNDC5, and irisin in humans?
Summary
In a small study of young healthy adults, 3 weeks of all-out cycling sprint interval training improved time to exhaustion but did not change skeletal muscle FNDC5 or overall circulating irisin. Plasma irisin responses differed by sex in exploratory analyses.
Methodology
- Young healthy non-obese adults in the sprint interval training study.
- 19 participants.
- Cycling.
- Work intervals: 30 s all-out maximal sprint.
- Recovery: 4 min recovery.
- Intensity: All-out.
- Not fully reported; sprint block varied by repetitions plus 4 min recoveries.
- 9 sessions over 3 weeks.
- 3 weeks.
- Two human studies; Study 2 was a pre-post sprint interval training intervention
- Time to exhaustion, and Browning biomarkers were tracked.
Outcomes
Time to exhaustion
Time to exhaustion improved after SIT.
38.7 +/- 4.4 to 49.3 +/- 7.4 min, p=0.048.
FGF21
FGF21 decreased after SIT.
338 +/- 78 to 251 +/- 36 pg/mL in abstract; p=0.046.
Irisin/FNDC5
FNDC5 and overall irisin did not change; irisin showed a sex interaction.
FNDC5 p=0.79; irisin overall p>0.787; sex x training p=0.012.
Insights
- Long recoveries with 30 s all-out cycling sprints can improve time-to-exhaustion in a short program.
- Biomarker findings should be treated as exploratory and not translated into consumer claims.
Limitations
- Small sample
- No control group
- Exploratory sex interaction
- Young healthy participants
- No adherence or adverse-event reporting
- Surrogate biomarker outcomes
Safety
- Adverse events were not reported.
- The article says participants were informed of risks and consented; biopsies were performed under local anesthesia.
- Session attendance, dropout, and tolerability values were not reported for the SIT intervention.