Why your body might not respond to exercise like someone else’s
Humans with obesity exhibit impaired circulating total, but not free, IGF‐1 response to acute endurance exercise
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
When people without obesity exercise, their bodies release more IGF-1 (a growth hormone) into the blood. But in people with obesity, this increase doesn’t happen — yet the useful part of IGF-1 (free IGF-1) stays the same.
Surprising Findings
Free IGF-1 levels remained unchanged in obese individuals despite a complete lack of rise in total IGF-1 and IGFBP-3.
It’s counterintuitive because total IGF-1 is usually seen as the main indicator of growth activity. The fact that the body preserves free IGF-1 — the only form that can bind to receptors — suggests a sophisticated, liver-driven adaptation to protect anabolic signaling.
Practical Takeaways
Don’t assume exercise is less beneficial for muscle repair if you have obesity — your body is actively preserving the key growth signal (free IGF-1) during workouts.
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
When people without obesity exercise, their bodies release more IGF-1 (a growth hormone) into the blood. But in people with obesity, this increase doesn’t happen — yet the useful part of IGF-1 (free IGF-1) stays the same.
Surprising Findings
Free IGF-1 levels remained unchanged in obese individuals despite a complete lack of rise in total IGF-1 and IGFBP-3.
It’s counterintuitive because total IGF-1 is usually seen as the main indicator of growth activity. The fact that the body preserves free IGF-1 — the only form that can bind to receptors — suggests a sophisticated, liver-driven adaptation to protect anabolic signaling.
Practical Takeaways
Don’t assume exercise is less beneficial for muscle repair if you have obesity — your body is actively preserving the key growth signal (free IGF-1) during workouts.
Publication
Journal
Physiological Reports
Year
2025
Authors
Eduardo Freitas, Lori R. Roust, Eleanna De Filippis, Matthew R. Buras, Brooke Brown, Christos S. Katsanos
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Claims (6)
When muscles are strongly activated during physical exercise, the body produces more insulin-like growth factor 1 (IGF-1), a protein involved in tissue growth and repair.
During short bouts of endurance exercise, people with obesity maintain the same levels of bioactive IGF-1 in their blood as lean individuals, even though overall IGF-1 and its binding protein increase less than in lean people.
Adults with obesity have a smaller increase in growth hormone after short bouts of endurance exercise than lean adults, and this may be linked to lower production of IGF-1 and IGFBP-3 by the liver.
In adults with obesity, changes in IGF-1 levels during endurance exercise are not related to the degree of insulin resistance, suggesting that insulin resistance does not directly control how IGF-1 responds to this type of physical activity.
When people with obesity do a single session of moderate-intensity cardio, their blood levels of IGF-1 and IGFBP-3 do not rise, unlike in lean individuals, suggesting the liver of people with obesity responds less to exercise in terms of producing these growth-related proteins.