Sports Medicine

, Volume 33, Issue 10, pp 771–781 | Cite as

Elucidating the Unexplained Underperformance Syndrome in Endurance Athletes

The Interleukin-6 Hypothesis
  • Paula J. RobsonEmail author
Review Article


The unexplained underperformance syndrome (UPS), previously known as the overtraining syndrome (OTS), has been defined as a persistent decrement in athletic performance capacity despite 2 weeks of relative rest. It has been proposed that UPS may be caused by excessive cytokine release during and following exercise causing a chronic inflammatory state and ‘cytokine sickness’. This article extends that hypothesis by proposing that time-dependent sensitisation could provide a model through which the aetiology of UPS may be explained. In this model, the principal abnormal factors in UPS are an increased production of and/or intolerance to interleukin (IL)-6 during exercise. Strategies to attenuate the IL-6 response to exercise that may also reduce an athlete’s susceptibility to UPS are proposed.


Prolonged Exercise Endurance Athlete Heat Stroke Hepatic Glucose Output Overtraining Syndrome 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



Funding for this study was provided by the RA Noakes post-doctoral fellowship fund, the Medical Research Council of South Africa, and Discovery Health Pty Ltd. The author has provided no information on sources of funding or on conflicts of interest directly relevant to the content of this review.


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Authors and Affiliations

  1. 1.UCT/MRC Research Unit for Exercise Science and Sports Medicine, Department of Human Biology, Sports Science Institute of South AfricaUniversity of Cape TownNewlandsSouth Africa

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