We know more than ever about overtraining syndrome and its effects on the body, but some of the underlying pieces of the puzzle are still missing. A recent study published in the Journal of Strength and Conditioning Research took aim at uncovering how overtraining affects the muscles on a molecular level.


In the study, researchers looked at several proteins that are involved in anabolism and catabolism. When I say proteins here, I don’t mean the kind that make up muscle, which is only a part of what proteins do. A protein is essentially a collection of amino acids bonded together. Our genes determine how they form. Because they can be very large molecules, proteins are a major part of what allows for the complexity of life.


The best known of the proteins examined in this study was IGF-1, or insulin-like growth factor 1 (pictured below). IGF-1 is actually a hormone, too. A hormone is a signaling molecule transported by the blood, and many of them are proteins. IGF-1 is well known for its anabolic effects. The term anabolic means it supports the development of muscle tissue.


The lesser known proteins that were looked at in this study were the anabolic proteins called MyoD and myogenin. These two proteins are known as transcription factors, which means they help regulate the expression of genetic material. MyoD and myogenin regulate the creation of muscle tissue. The catabolic protein called MAFbx, which helps with the breakdown of muscle tissue, was studied as well.

Mice were used in this study, since, according to the researchers, they are easier to examine from a whole-muscle interaction perspective. The mice underwent a strenuous workout with about a fifteen percent greater load than normally recommended for building size and strength. They exercised at that level for five days a week for twelve weeks to keep the recovery time limited.


We know many of the features that comprise overtraining, which is what this study was designed to induce. Elevated stress hormones like cortisol and other stress markers like creatine kinase, reduced anabolic hormones like testosterone, increased incidence of illness and injury, reduced performance, and poor mood are all known symptoms of overtraining. The researchers theorized that alterations to IGF-1, MyoD, myogenin, and MAFbx could be added to that list.


Indeed, they were correct. The catabolic protein MAFbx was upregulated, which means its expression increased, by a full twenty percent. Even more dramatically, the anabolic proteins MyoD, myogenin, and IGF-1 were downregulated by 27%, 29%, and 43%, respectively. It may be hard to get an idea of what those numbers really mean, so the researchers also took the more common measurement of muscle cross-sectional area (muscle thickness). The above change in proteins amounted to a seventeen percent reduction in muscle size.


So science now has a new way of determining overtraining status by measuring these proteins. It would probably be a challenge to force yourself to this extreme degree of training, but just be aware that more training is not always better for any athletic goal. Even subtle losses in muscle are the opposite of most peoples' goals.



1. Rodrigo Souza, et. al., “Resistance Training With Excessive Training Load and Insufficient Recovery Alters Skeletal Muscle Mass-Related Protein Expression,Journal of Strength and Conditioning Research, DOI: 10.1519/JSC.0000000000000421


Photo courtesy of Shutterstock.

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