Does exercise-induced inflammation serve a useful purpose across the adult age span?

Abstract

Inflammation is a protective biological response involving immune cells, blood vessels and molecular mediators, initiated upon the induction of cell injury (Abbas, Lichtman, & Pillai, 2007). The purpose of nflammation is to both eliminate the cause of the injurious agent (Abbas et al., 2007) as well as remove dead cells and tissues, damaged from the initial assault (Lapointe, Frenette, & Côté, 2002), and to initiate tissue repair (Ricciotti & FitzGerald, 2011). Inflammation as an event is a generic response to any injurious insult, which includes exercise-induced injury (Nehlsen-Cannarella et al., 1997). Exercise-induced muscle damage is defined as an injury from a mechanical force applied externally, causing structural stress or strain, resulting in cellular or tissue responses (Mueller & Maluf, 2002).

An acute inflammatory response is sometimes instigated during exercise (Nehlsen-Cannarella et al., 1997); its initiation and magnitude depend upon the degree of physiological stress applied during the exercise bout (McFarlin, Flynn, Stewart, & Timmerman, 2004). Exercise-induced inflammation is typically seen in endurance sports where there is overuse of specific tissues (McFarlin et al., 2004). Physiological stress increases as intensity, duration and internal stimuli (e.g., blood glucose levels) increase (McFarlin et al., 2004). Thus, prolonged and intensive exercises significantly increase the induction of and the magnitude of an inflammatory response (McFarlin et al., 2004).

Exercise-induced inflammation also stimulates the activation of the hypothalamic-pituitary adrenocortical (HPA) axis, characterised by elevated levels of cortisol and other mediators, inducing immune suppressive effects and thereby reinstating immune homeostasis (Tsigos & Chrousos, 2002). However, the immunosuppressive effects of the HPA axis may be detrimental to individuals if over-stimulated (Tsigos & Chrousos, 2002).Various methods have been employed in training regimes to counteract this inflammatory response Exercise-Induced Inflammation 7 (Bleakley, McDonough, & MacAuley, 2004; Gleeson, Nieman, & Pedersen, 2004; Quintero, Wright, Fu, & Huard, 2009). Carbohydrate supplementation is one method (Gleeson et al., 2004; McFarlin et al., 2004; Mitchell et al., 1998; Nehlsen-Cannarella et al., 1997; Nieman et al., 2004; Nieman et al., 1998; Scharhag, Myer, Auracher, Gabriel, & Kindermann, 2006). Others, such as cryotherapy (Bleakley et al., 2004) and RICE (rest, ice, compression, and elevation; Quintero et al., 2009), are also commonly used to reduce the exercise-induced inflammatory response under conditions where muscle soreness and/or injuries occur following physical activity (Bleakley et al., 2004; Quintero et al., 2009). The underlying theory is that reducing the inflammation will improve muscle tissue recovery (Bleakley et al., 2004; Quintero et al., 2009).

The exercise-induced inflammatory response is necessary for performance adaptation (Kurtz, Loebig, Anderson, DeMeo, & Campbell, 1999), although, it may also lead to injury and is often associated with pain or discomfort by the individual (Abbas et al., 2007). Considering these two, opposing concepts, it would be valuable to understand the appropriate management of exercise-induced inflammation for both injury prevention and performance gains.

Further complicating this question are external factors, which can enhance or reduce systemic inflammation (Gomez, Nomellini, Faunce, & Kovacs, 2008; Weiskopf, Weinberger & Grubeck-Loebenstein, 2009). In particular, age has significant impacts on both immune function and underlying inflammatory status (Franceschi et al., 2007; Gomez et al., 2008; Weiskopf et al., 2009). For example, aging impacts immune function by weakening immune responses to infections (Gomez, Boehmer, & Kovacs, 2005).

Therefore, the purpose of this paper is to answer two questions: 1) ‘Does Exercise- Induced Inflammation Serve a Useful Purpose?’; and 2) ‘How Does Aging Affect this Process?’ To address these questions, this paper will first: i) review the role of inflammation as part of the Exercise-Induced Inflammation 8 innate immune response; ii) examine the positive and negative consequences of the exercise induced inflammatory response; and iii) outline the age-related effects on both the immune system and underlying inflammatory status.