5 Functions of IGF-1

anabolic anabolism hormones muscle growth muscle physiology Jun 10, 2022
Photo credit: Samer Daboul

Photo credit: Samer Daboul

What is it? 

IGF-1 stands for insulin-like growth factor - the 1 is representative of the type of binding protein, there are 6 different binding proteins - IGF-2, IGF-3, IGF-4, IGF-5, & IGF-6. 

It’s a hormone that promotes growth and acts like insulin. It’s produced in the liver then circulated into the bloodstream and acts upon the muscle and bone.

IGF-1 is mediated by growth hormone following activation by testosterone:

  1. Resistance training > increased testosterone
  2. Increased testosterone > growth hormone 
  3. Increased growth hormone > delayed response of IGF-1
  4. IGF-1 is also regulated by the thyroid hormone 

The delayed response occurs 8-24 hours after resistance training

IGF-1 Function:

  1. Contributes to protein anabolism (muscle growth)
  2. Reduces proteolysis (tearing muscle down)
  3. Inhibits glucocorticoids (hormones that tear muscle down into amino acids and convert them into glucose)
  4. Increase bone mineral density (building stronger bones)
  5. Increase insulin sensitivity (encourages circulating blood glucose to be utilized for energy)

Why is it important? 

Muscle Growth: IGF-1 promotes anabolism, or anabolic - to grow or synthesize, build, or repair molecules and tissues, in this case, to grow muscle

Mechano growth factor helps differentiate stem cells into forming new muscle cells or to form proteins. 

Within skeletal muscle, IGF-1 is actually referred to as mechano growth factor which contributes to muscle growth through muscle protein synthesis. So mechano growth factor encourages some stem cells to differentiate into new muscle cells through the demands of resistance training on the body. 

Tearing Muscle Down

Catabolism, or proteolysis, is the tearing down of muscle. This process is also referred to as muscle protein degradation. 

Proto = protein

Lysis = breakdown

IGF-1 inhibits the enzymes that tear down muscle since IGF-1’s role is to grow tissues not break them down. 

Balancing Anabolism & Catabolism

IGF-1 helps promote more anabolism than catabolism. Ultimately, we want more muscle protein synthesis than muscle protein degradation to grow and strengthen muscles, not tear them down and weaken them. 

Inhibits Glucocorticoids

Glucocorticoids promote amino acids to be converted into glucose to be utilized for energy. 

The primary glucocorticoid that we’re concerned with as strength coaches is cortisol. Cortisol is a catabolic hormone involved in carbohydrate metabolism. In skeletal muscle, cortisol sends a signal to the body to break down amino acids into glucose. So we want to reduce these catabolic effects as much as possible. 

IGF-1 inhibits glucocorticoids, so it actually helps spare muscle tissue from being converted into glucose for energy. So IGF-1 helps promote muscle building in this way. 

Increased Bone Mineral Density

When we load bone with resistance, we’re sending signals to build bone tissue through IGF-1 by promoting the development of osteoblasts that increase bone tissue & mineralization and therefore reduce the function of osteoclasts, the cells that break bone tissue down. 

Increased Insulin Sensitivity

IGF-1 promotes insulin release within the bloodstream and associated glucose uptake into the cell for energy use. When the body uses glucose for energy metabolism, it spares the breakdown of muscle into amino acids to meet energy demands. 

The 2 Primary Takeaways

IGF- has both growth-like and insulin-like properties for both muscle & bone. 


Support & Courses Available

Ready for more support about the endocrine responses to resistance exercises to help you prep for the CSCS exam? Join our Facebook Group “Strength and Conditioning Study Group” here. 

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