What Are The Effects Of Overtraining In Swimmers?

What Are The Effects Of Overtraining In Swimmers?

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Background Overtraining In Swimming

Overtraining and overreaching are common in the sport of swimming. No matter if you are a high or low volume advocate, swimming requires countless hours in the pool putting one at risk for overtraining.

Some coaches feel overtraining is a beneficial part of training to ‘break-down’ the athlete and make them stronger, despite the literature suggesting overtraining causes increases in inflammation and decreases in muscle mass. However, the exact mechanism and results of overtraining are not well documented.

Xiao et al. looked to analyze the influence of 11 weeks of overtraining of treadmill training on rats.

What was done

30 Winstar rats underwent one-week acclimatization, then 10 were put into a control group, then the rest were put on 11 weeks of an overtraining protocol progressing to four one hour training sessions a day. Of the remaining 20 rats, after the 11 weeks of overtraining, half recovered for seven days.

Blood work of the rats was performed 36 hours after and 7 days after the last training session. A muscle was harvested, prepared, and ribonucleic acid (RNA) was extracted.  


The rats acclimated well with the overtraining for the first eight weeks, but needed assistance from the eight to the eleventh week, leading to a decrease in mental state. Blood assay showed testosterone, and hemoglobin decreases in the over-trained rate in a combination of a decrease in weight.

The size of the gastrocnemius muscle also decreased by 23.6% in the overtraining group and was still smaller after 7 days. Creatine kinase levels were also higher in the overtraining group. Increases in interleukin (IL)-6 and transforming growth factor (TGF)-β1 mRNA in the muscles of the overtraining group compared with the sedentary group. Furthermore, the predominantly anti-inflammatory cytokine, IL-10, decreased significantly in the overtraining group compared to the sedentary group (decreased by 63 %). Although IL-6 and TGF- β1 had a tendency to normalization after 1 week of recovery, the level of the IL-10 mRNA in the muscles of the overtraining recovery group was lower than the sedentary group. Cyclooxygenase (COX)-2 mRNA decreased dramatically, similar to null mutation of COX-2 or COX-2 inhibitor. Both COX-2 and uPA decreased significantly in the overtraining group, which is consistent with the findings of previous reports.


This study indicates over-training results in muscle injury and the inhibition of skeletal muscle growth. This is due to an increase in pro-inflammatory cell signalers (cytokines) and a decrease in anti-inflammatory cytokines. Also, cox-2 and uPA are necessary for muscle growth but are blunted in the overtraining group.

Practical Implication

Swimming is a unique, unnatural sport for humans. As a result, long hours in the pool are required to learn the appropriate motor patterns for high performance. However, over-training should be avoided due to potential decreases in muscle size and an increase in inflammation (which hinders a swimmer’s ability to adapt to training per the super compensation response.). Despite the suggestions in this study, conclusions drawn should be taken with a grain of salt, as it was performed on rats on a treadmill, not swimmers in the pool.


  1. Xiao W, Chen P, Dong J. Effects of Overtraining on Skeletal Muscle Growth and Gene Expression. Int J Sports Med. 2012 May 16.

Originally Posted June 2012

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