Research
Hormonal
Chronic exercise training increases muscle PGC1A and FNDC5 mRNA expression in humans, but this transcriptional increase does not correlate with plasma irisin levels or subcutaneous fat browning (UCP1).
Your muscles do adapt to exercise by increasing the machinery (PGC1A/FNDC5 mRNA) to potentially produce irisin. However, this does not mean more irisin enters your blood or that your fat turns brown. The local muscle changes are real, but the systemic hormonal effect is not.
GoodQualifiesHIGH confidence
Skeletal muscle mRNA for PGC1A and FNDC5 correlated and both PGC1A and FNDC5 mRNA levels increased after 12 weeks of training... There was little effect of 12 weeks of training on selected browning genes in subcutaneous adipose tissue. UCP1 mRNA did not correlate with FNDC5 expression in subcutaneous adipose tissue or skeletal muscle or with irisin levels in plasma.
Why this rating
Robust molecular analysis of muscle, fat, and plasma.
Source
The effects of acute and chronic exercise on <scp>PGC</scp>‐1α, irisin and browning of subcutaneous adipose tissue in humans
Frode Norheim et al. · FEBS Journal · 2013
DOI 10.1111/febs.12619
rct · n=26Cited 559×
Read the paper DOI resolved against Crossref · corpus check 2026-06-10
More from this paper
- Twelve weeks of combined endurance and strength training in humans does not increase circulating irisin levels and may actually reduce them, despite increasing muscle FNDC5 mRNA expression.Good
- Acute exercise (45 min at 70% VO2max) causes a transient ~1.2-fold increase in plasma irisin immediately post-exercise, which returns to baseline within 2 hours.Good
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