Intramuscular fat or Intramuscular triglycerides (IMTG) is located throughout skeletal muscle

Skeletal muscle

Skeletal muscle is a form of striated muscle tissue existing under control of the somatic nervous system- i.e. it is voluntarily controlled. It is one of three major muscle types, the others being cardiac and smooth muscle...

 and is responsible for the marbling

Marbled meat

Marbled meat is meat, especially red meat, which contains various amounts of intramuscular fat, giving it an appearance similar to a marble pattern.- Selective breeding :Marbling can be influenced by selective breeding...

 seen in certain cuts of beef

Beef

Beef is the culinary name for meat from bovines, especially domestic cattle. Beef can be harvested from cows, bulls, heifers or steers. It is one of the principal meats used in the cuisine of the Middle East , Australia, Argentina, Brazil, Europe and the United States, and is also important in...

. In humans, excess accumulation of intramuscular fat is associated with insulin resistance

Insulin resistance

Insulin resistance is a physiological condition where the natural hormone insulin becomes less effective at lowering blood sugars. The resulting increase in blood glucose may raise levels outside the normal range and cause adverse health effects, depending on dietary conditions. Certain cell types...

 and type 2 diabetes. The human immunodeficiency virus (HIV)-lipodystrophy

Lipodystrophy

Lipodystrophy is a medical condition characterized by abnormal or degenerative conditions of the body's adipose tissue. A more specific term, lipoatrophy is used when describing the loss of fat from one area...

 syndrome is associated with over-accumulation of intramuscular fat which may contribute to AIDS wasting syndrome.

Diabetes

Ten years ago, it was believed that an increase in IMTGs was responsible for increased insulin resistance. However, the finding that athletes as well as obese individuals have high IMTG levels confounded these findings. It is now believed that it is the IMTG metabolites, such as diacylglycerol and ceramide, that are responsible for the insulin resistance. There are variable results about which of these metabolites is most important, as some studies have shown that neither has an effect while others have shown one has but the other has not. In studies that have demonstrated their effects, their mechanism has been shown to be via activation of protein kinase C theta. PKC theta promotes serine phosphorylation of IRS-1, thereby inhibiting the insulin signalling cascade.

Insulin Resistance

Increased supply of adipose tissue

Adipose tissue

In histology, adipose tissue or body fat or fat depot or just fat is loose connective tissue composed of adipocytes. It is technically composed of roughly only 80% fat; fat in its solitary state exists in the liver and muscles. Adipose tissue is derived from lipoblasts...

 correlates with the increased accumulation of IMTG which both can lead to insulin

Insulin

Insulin is a hormone central to regulating carbohydrate and fat metabolism in the body. Insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle....

 resistance in the muscles. Athletes often do not exhibit this correlation as they are typically insulin sensitive while having high levels of IMTG. It is thought that the improved efficiency of trained skeletal muscles

Skeletal muscle

Skeletal muscle is a form of striated muscle tissue existing under control of the somatic nervous system- i.e. it is voluntarily controlled. It is one of three major muscle types, the others being cardiac and smooth muscle...

 prevents the development of insulin resistance.

Exercise

"Intramuscular triacylglycerol (IMTG) represents an energy store that can be used during exercise, when it may contribute up to 20% of total energy turnover depending on diet, gender, and exercise type."

It is thought that a low calorie diet and exercise induced proteins (Sterol

Sterol

Sterols, also known as steroid alcohols, are a subgroup of the steroids and an important class of organic molecules. They occur naturally in plants, animals, and fungi, with the most familiar type of animal sterol being cholesterol...

regulatory element-binding proteins) are what cause high levels of IMTG in the skeletal muscle of trained athletes. This is in contrast to the build-up of IMTG in the obese which correlates to high levels of adipose tissue.

Women have been shown to use more IMTG during exercise than men which directly correlates to the higher IMTG content in women over men.