Hormonal
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.
If you are training to boost irisin for fat loss, this 12-week study suggests it won't work as expected; irisin levels actually decreased. However, your muscle genes (PGC1A and FNDC5) did upregulate. Focus on the direct metabolic benefits of exercise rather than expecting a specific hormonal spike in irisin.
We observed no enhancing effect of long-term training on circulating irisin levels, and little or no effect of training on browning of subcutaneous white adipose tissue in humans.
Why this rating
Randomized controlled trial with 26 participants, using two different ELISA kits to confirm findings, reducing assay-specific artifact risk.
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
More from this paper
- 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
- 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).Good
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