GLOSSARY

Fibronectin Type III Domain-Containing Protein 5 (FNDC5)
FNDC5 is a membrane protein from which irisin-related peptides can be generated.

Evidence for muscle-derived signals. A candidate myokine requires evidence of muscle production and release. Endocrine action additionally requires biologically relevant delivery and a response at a distant target. Expression within muscle or an increase in blood alone does not establish this entire chain.

Specific considerations. Expression, processing and measured circulating product are distinct experimental observations.

Interpreting exercise studies. Sampling time, muscle damage, other tissue sources and assay specificity affect measured exerkines. Animal or cell findings can identify mechanisms but do not guarantee a proven human performance benefit. Local action may be important even without a detectable circulating rise.