GLOSSARY

Hepatic and Local IGF-1 Production
IGF-1 production occurs in liver and in many peripheral tissues. Hepatic output contributes substantially to circulating concentrations, while local production can support autocrine and paracrine signaling.

Different regulatory environments

GH is an important stimulus, but local mechanical, nutritional and cellular inputs also influence tissue expression. The relative contribution varies by organ and physiological state.

Blood and tissue differ

• Serum IGF-1 does not directly measure local synthesis or receptor activation inside skeletal muscle, bone or tendon.
• Local binding proteins and processing further modify exposure.

Exercise relevance

A training adaptation can involve local growth-factor regulation without a matching rise in circulating IGF-1. Mechanistic claims therefore need the relevant tissue measurements rather than assuming that serum changes represent every local response.