The Role of Insulin in Weight Training

Insulin is one of the body’s most important hormones, and it is of particular interest for bodybuilders who train naturally.


Insulin’s primary role is to allow nutrients in the bloodstream to enter body tissues. Insulin causes the body’s fuel sources to be stored and it promotes glycogen formation, muscle formation, and storage of fat. Even in healthy people, an abnormality in insulin secretions stemming from poor eating habits and lack of exercise can cause serious metabolic disorders. For example, prolonged poor eating habits can result in type 2 diabetes accompanied by obesity or, at the other end of the spectrum, hypoglycemia.

For weight training purposes (and in the interest of general health), having a 6-hour-fasted blood sugar test performed can help ensure that a person’s insulin secretions are in good shape. For reference, the normal range for fasted blood sugar is between 70 and 110 mg/dl.

The bloodstream’s storage capacity for glucose is about 80 calories. When recently ingested glucose raises the blood sugar level in excess of this capacity, the pancreas releases insulin into the bloodstream to transport the excess glucose to body tissues. This excess amount of glucose is said to be insulin-carried. Insulin must be present for the uptake of glucose most all of the body’s tissues, with the exception of the brain and the liver. The cells in these organs obtain their glucose from another non-insulin dependent transporter.

If there is still more insulin-carried blood glucose after the liver and muscle tissue have taken in all they can, the excess will be rapidly stored in extra-muscular fat cells. It is important to note that muscle tissues take up insulin-carried glucose very gradually in contrast to fat cells, which take up this form of glucose very quickly.

Insulin & Amino Acids

As mentioned, one of insulin’s functions is that it must be present in order to open insulin receptor sites in muscle. This allows amino acids to move into the tissue fibers and serve as catalysts and as building blocks for repair and growth. Eating proteins, however, does not stimulate insulin release into the blood. Ensuring that insulin will be present for amino acid uptake into muscles (essential for protein synthesis) means ingesting sufficient amounts of carbohydrates together with complete proteins in order to stimulate the pancreas to make insulin available.

Interestingly, exercise has an “insulin-like” effect on the muscles, and strength trainees might do well to consider incorporating this exercise-induced effect into their workouts.

Anabolism is most effective when insulin is in steady supply, which in turn allows for the continual uptake of glucose and amino acids by recovering muscle cells. The most effective way for this to happen is to ingest complete proteins and sufficient amounts of complex carbohydrates frequently throughout the day. This will provide the body with steady and moderate amounts of insulin.

In addition, since amino acids are present for protein synthesis for only about 3-4 hours, complete proteins and complex carbohydrates should be ingested every 3-4 hours. When someone is working to build muscle, it is important to time meals in order for insulin to be present and anabolism to occur more efficiently. Insulin also activates several of the enzymes that are directly involved in glycogen synthesis.

What are Optimal Insulin Secretions?

Ingesting simple sugars cause blood sugar to rise quickly, causing an over-release of insulin. This leads to a drop in blood sugar level followed by a drop in insulin level. One way to avoid this effect and plan for optimal insulation secretions is to consult a glycemic index chart. The index classifies carbohydrates according to their absorption rates into the bloodstream on an empty stomach. The glycemic index rates foods on a scale of 0-100. The higher the number, the quicker the rate of absorption. The rate of absorption should be as low as possible to avoid an over-release of insulin. Even though certain natural healthy foods such as potatoes and carrots are simple sugars and rate a bit high on this index, they are still a good food choice if they are combined with other low-glycemic-index carbohydrates. This will act to moderate the rate of absorption of the portion of these foods that contain simple sugar carbohydrates. Soluble fiber such as the kind contained in most natural complex carbohydrates acts to slow the rate of absorption.

It is also important to note that intense training opens muscle tissue insulin receptor sites. This suggests that the weight-training participant should eat a moderate sized pre-workout meal and a reasonably sized post-workout meal both consisting of quality complex carbohydrates as well as a quality source of lean, complete proteins.


1. Mead, J.R., Irvine, S.A., Ramii, D.P. (2002). Lipoprotein lipase: structure, function, regulation and role in disease. Journal of Molecular Medicine, Dec; 80(12):753-69. Epub 2002 Oct 24.

2. Jeukendrup, A.E. and Gleeson M. (2010). Sports nutrition: An introduction to energy production and performance, 2nd ed. Human Kinetics, Champaign, IL


These resources are for the purpose of personal trainer growth and development through Continuing Education which advances the knowledge of fitness professionals. This article is written for NFPT Certified Personal Trainers to receive Continuing Education Credit (CEC). Please contact NFPT at 800.729.6378 or [email protected] with questions or for more information.