Don’t let overtraining trip you up—the consequences are severe! You can suffer significant muscle loss, inflammation, and changes in muscle fiber types.
There’s a fine line between overtraining that causes physiological damage and overreaching to shock the body into making significant strength and size gains. Let’s look at a recent study performed on rats that provides insight on the mechanism behind muscle atrophy during overtraining.
This study, published in The Anatomical Record compared muscle cross-sectional area and fiber type biopsies in a control group and a training group. The training group performed weighted sets of jumps in and out of the water five days a week for 12 weeks. The rats carried a weighted vest that started at 60 percent of body weight and progressively increased to 85 percent of body weight over the four weeks. The number of jumps per day varied from 20 to 50 a day.
Results showed that the training produced a significant loss of muscle mass and body weight after 12 weeks. There was a dramatic muscle atrophy in the leg muscles and a decrease in muscle cross-sectional area that ranged from 15 to 19 percent, depending on fiber type. In addition, there was a fiber type shift to more of the fastest twitch fibers—comparable to the type IIX in humans—but this was not a favorable physiological change. Although strength and power athletes need a greater proportion of strong type II fibers, the fiber type shift didn’t mean that the fibers were stronger—actually they were weaker, but there were more of them.
The muscle atrophy occurred due to muscle protein breakdown, which was indicated by higher blood amino acid content. The muscles require amino acids to remodel and repair from high-intensity training, but since there are not enough ingested in the diet, muscle loss occurs. This is why it’s possible to support the body through a short-term overtraining phase by increasing nutrient intake by 50 percent over normal requirements, but it’s not possible over a 12-week training cycle.
There was also a decrease in DNA content per muscle that may be due to a loss of satellite cells, which are cells located under the muscle fibers. When activated, they proliferate, differentiate, and fuse with muscle fibers. Researchers suggest the overtraining promoted a muscle loss “disease” or myopathy that was characterized by the persistent loss of satellite cells and protein muscle degradation.
There are many markers of overtraining but a couple of practical indicators of overtraining include the following:
• Altered sleep or inability to get enough sleep despite adequate rest time.
• Mood disturbances, which can be a strong indicators of hormonal imbalances from training or an exhausted central nervous system (CNS).
• Decreased grip strength as measured by a dynamometer (a hand-held device that measures grip strength—see the link to an article at the bottom for information) will indicate lack of CNS recovery.
• Decreased vertical jumping ability is another measure of poor CNS recovery.
• Low growth hormone, cortisol, and blunted ACTH (an adrenal hormone) are indicators of overtraining. This method is only practical if regular blood draws can be done to test for chronically low adrenals.
• Low blood or urinary pH (below 7) as measured by a simple pH test indicate overtraining because elevated cortisol will decrease pH, as will a buildup of waste byproducts in the blood from excessive intense training.
For more information on methods for testing and avoiding overtraining, check out Practical Methods to Avoid Overtraining
De souza, R., Aguiar, A., et al. High-Intensity Resistance Training with Insufficient Recovery Time Between Bouts Induce Atrophy and Alterations in Myosin Heavy Chain Content in Rat Skeletal Muscle. The Anatomical Record. 2011. 294(8), 1393-1400.