Cytokine hypothesis of overtraining: a physiological adaptation to excessive stress?

Abstract

Overtraining syndrome (OTS) is a condition wherein an athlete is training excessively, yet performance deteriorates. This is usually accompanied by mood/behavior changes and a variety of biochemical and physiological alterations. Presently, there is no global hypothesis to account for OTS. The present paper will attempt to provide a unifying paradigm that will integrate previous research under the rubric of the cytokine hypothesis of overtraining. It is argued that high volume/intensity training, with insufficient rest, will produce muscle and/or skeletal and/or joint trauma. Circulating monocytes are then activated by injury-related cytokines, and in turn produce large quantities of proinflammatory IL-1beta, and/or IL-6, and/or TNF-alpha, producing systemic inflammation. Elevated circulating cytokines then co-ordinate the whole-body response by: a) communicating with the CNS and inducing a set of behaviors referred to as "sickness" behavior, which involves mood and behavior changes that support resolution of systemic inflammation: b) adjusting liver function, to support the up-regulation of gluconeogenesis, as well as de novo synthesis of acute phase proteins, and a concomitant hypercatabolic state; and c) impacting on immune function. Theoretically, OTS is viewed as the third stage of Selye's general adaptation syndrome, with the focus being on recovery/survival, and not adaptation, and is deemed to be "protective," occurring in response to excessive physical/physiological stress. Recommendations are made for potential markers of OTS, based on a systemic inflammatory condition.

Regulation of nitric oxide production in limb and ventilatory muscles during chronic exercise training

“…Possible explanations for this finding include that, in our study, exercise type and intensity were insufficient to provoke muscle fiber injury, and, consequently, very little secondary leukocyte infiltration, a potential source for iNOS induction, might have occurred. It is also possible that a certain threshold intensity of muscular activity is required before exercise leads to enhanced production of proinflammatory cytokines inside muscle fibers (23). This threshold activity might not have been reached in the exercise program adopted in this study.…”

High‐Intensity Resistance Training with Insufficient Recovery Time Between Bouts Induce Atrophy and Alterations in Myosin Heavy Chain Content in Rat Skeletal Muscle

“…Petibois et al (2003) observed that overtrained individuals presented higher amino acids and lower protein blood accumulation in response to exercise than well-trained individuals, suggesting that proteins were catabolized for amino acid supply during exercise. This increased requirement for amino acids during hypermetabolism is partly satisfied by an augmentation of muscle proteolysis, the major storage pool of amino acids, and by a concomitant reduction in muscle anabolism (Smith, 1999). In addition, Seene et al (2004) showed that during overtraining condition, degradation increased and a decreased muscle protein synthesis rate lead to a decrease in muscle mass, particularly in fast twitch muscles.…”

“…Naturally, training and competition are associated with a mild muscle tissue trauma followed by recovery. When adequate recovery is allowed, it results in an ''overshoot'' phenomenon, an adaptive process often called ''adaptive microtrauma'' (Smith, 1999). However, when intensity/volume training is abruptly increased and rest/recovery time between bouts is insufficient, mild trauma could develop into a more chronic, severe form of tissue trauma.…”

The implication of the binomial nutrition-immunity on sportswomen's health

“…In fact, it has been pointed out that several mechanisms which involve hormone alterations and are developed in eating disorders are displayed to save energy, get adapted to deficient intakes, and maintain physiological functions within the normal range (Marcos et al, 1997. Moreover, in individuals under excessive training, hormone alterations are involved in the mechanisms affecting immunocompetence (Smith, 2000). It is generally admitted that athletes are competitive, train at very high levels with inadequate rest, consume too few calories, avoid fat, and may be at increased risk of infections (Venkatraman et al, 2001).…”