Exercise Induced Muscle Damage And Its Impact On Power Training
What is EIMD?
Exercise induced muscle damage (EIMD) is a condition commonly experienced by athletes that can result in a great deal of pain and discomfort that increases over 24 to 48 hours lasting for a few days until the athlete recovers (Howatson & Van Someren, 2008). Novel exercises that the body is not accustomed to, eccentric training, or those that involve high intensity and volume can lead to EIMD (Doncaster & Twist, 2012; Ebbeling & Clarkson, 1989). EIMD can manifest itself in different physiological conditions (Kuipers, 2008). These include delayed onset muscle soreness (DOMS), morphological changes such as swelling of the muscles, increase in intra-muscular protein and reduced range of motion (ROM) (Ebbeling & Clarkson, 1989). This leads to a decrease in athletic performance due to slower reaction times, co-ordination and a decrease in the rate of force development (RFD) (Doncaster & Twist, 2012). In particular, EIMD has a strong influence on power training for athletes. Power is a product of force and velocity and is an important variable for success in many sports (Nottle & Nosaka, 2007). Therefore it is in the interest of the strength and conditioning (S&C) coach to understand how EIMD impacts on power.
Proposed Mechanisms of EIMD
Two primary mechanisms have been proposed to be associated with EIMD as a result of eccentric based exercises. Specifically, these mechanisms are described as metabolic and mechanical (Ebbeling & Clarkson, 1989).
The Metabolic Mechanism
Metabolic damage brought on by EIMD has been linked to cell damage as a result of ischaemia or hypoxia after long duration exercise (Howatson & Van Someren, 2008). Ischaemia can occur as a result of insufficient supply of blood to the muscles (Tee, Bosch, & Lambert, 2007), whereas hypoxia is a condition resulting in the restriction and reduction of oxygen reaching the tissues (Korner, 1959). Changes in ion concentrations from metabolic events such as ischaemia and hypoxia share similar characteristic seen in muscle damage that involve increases in metabolic waste, waste accumulation and ATP deficiency. However, this association between metabolic damage and EIMD has not been clearly linked (Ebbeling & Clarkson, 1989).
The Mechanical Mechanism
The second mechanism relates to the mechanical damage of the muscle which is usually used to refute the metabolic damage hypotheses as it relates to the structural damage that occurs due to the mechanical load that the muscle microstructures undergo (Howatson & Van Someren, 2008). Researchers continually find that eccentric exercise uses less energy and therefore produces less metabolic waste. However eccentric contractions still result in greater muscle damage when compared to both concentric and isometric muscle action (Ebbeling & Clarkson, 1989). Eccentric muscle contraction is mechanically different when compared to concentric or isometric contractions, because it requires the muscle to actively lengthen under contraction, and this has been shown to cause direct structural damage to the muscle fibers (Lieber & Friden, 1993). Many basic activities involving eccentric contractions such as jumping, landing or sprinting can induce muscle damage as a consequence of the mechanical mechanism of EIMD (Dugan & Bhat, 2005; Ebbeling & Clarkson, 1989).
Signs and Symptoms
Having identified the primary mechanisms of EIMD it is also important to highlight some of the signs and symptoms associated with EIMD in order for the S&C coach to recognise the condition in an athlete. DOMS a symptom of EIMD, which manifests itself as pain and discomfort experienced by athletes is a clear indicator that EIMD has occurred (Friden, 2002). DOMS occurs post exercises with pain and discomfort gradually building over the first day and usually peaking 24 hours after exercise (Nottle & Nosaka, 2007). The pain and discomfort will then gradually decrease but can last for a few days before it completely clears (Friden, 2002). Other symptoms associated with EIMD include swelling of the trained muscles, changes in muscle girth leading to muscle aches and pain and a decrease in the RFD due to a loss of ROM and stiffer joints (Szymanski, 2001; Doncaster & Twist, 2012). There are also changes in blood proteins such as creatine kinase (CK) and myoglobin (Chen et al., 2013; Ebbeling & Clarkson, 1989).
EIMD and Athletic Performance
How does EIMD affect power training?
Research examining the effects of EIMD on strength is unexpectedly higher than that looking at power since power is also a very important indicator of athletic success in various sports (Nottle & Nosaka, 2007). According to Nottle & Nosaka (2007) eccentric exercise can lead to a decrease in both strength and power output, however the overall reduction in power is not significant. On the other hand Byrne, Twist, & Eston (2004) found that unlike strength, muscle power does not recover in a linear fashion and actually decreases for one to two days before recovering and suggested that this can be as a result of DOMS and inflammation. The authors also found that EIMD from endurance training or plyometric exercise can lead to a decrease in ground reaction forces, maximal force and an increase muscle and joint stiffness leading to lower muscle power output.
Prevention and Treatment
It is important for the S&C coach to identify EIMD markers and work with the athlete to reduce the symptoms of EIMD in order to avoid injury (Howatson & Van Someren, 2008). As previously discussed, EIMD has a direct impact on athletic performance, since the athlete is unable to generate force optimally due to symptoms such as DOMS (Nottle & Nosaka, 2007). Table 1 shows the sequence of events following eccentric exercise and suggested treatment for the different phases of the process. Mechanical damage is shown to have muscle structure damage and inflammatory responses resulting in different symptoms. The treatment column shows the recommend treatments at the different phases of DOMS.
Repeated Bout Exercise Training
Symptoms of EIMD can also be significantly decreased using the repeated bout effect (RBE) (Howatson & Van Someren, 2008). RBE allows for a protective adaptation to future eccentric training through a single session of eccentric training (McHugh, Connolly, Eston, & Gleim, 1999). A number of theories have been proposed to explain RBE but their mechanisms are still not fully understood (McHugh, 2003). The theories include adaptions as a result of cellular, mechanical or neural changes (McHugh, 2003). RBE training involves using two to ten repetitions of maximal eccentric contractions to provide protection from future DOMS for possibly a number of months (McHugh et al., 1999). This protection appears to be muscle specific (McHugh, 2003).
Take Home Message
EIMD can lead to a great deal of discomfort and hinder training and performance. A good understanding of the mechanisms of EIMD will help identify the signs and symptoms associated with the condition including DOMS and the best course of prevention or treatment. S&C coaches can utilise the RBE to protect against future muscle pain and discomfort by utilising a single bout of eccentric training session.
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