Abstract
The appearance of creatine kinase (CK) in blood has been generally considered to be an indirect marker of muscle damage, particularly for diagnosis of medical conditions such as myocardial infarction, muscular dystrophy, and cerebral diseases. However, there is controversy in the literature concerning its validity in reflecting muscle damage as a consequence of level and intensity of physical exercise. Nonmodifiable factors, for example, ethnicity, age, and gender, can also affect enzyme tissue activity and subsequent CK serum levels. The extent of effect suggests that acceptable upper limits of normal CK levels may need to be reset to recognise the impact of these factors. There is a need for standardisation of protocols and stronger guidelines which would facilitate greater scientific integrity. The purpose of this paper is to examine current evidence and opinion relating to the release of CK from skeletal muscle in response to physical activity and examine if elevated concentrations are a health concern.
Highlights
creatine kinase (CK) is a compact enzyme of around 82 kDa that is found in both the cytosol and mitochondria of tissues where energy demands are high
CK catalyzes the reversible phosphorylation of creatine to phosphocreatine and of ADP to ATP [3, 4], and as such it is important in regeneration of cellular ATP: Phosphocreatine + MgADP− + H+ ⇐⇒ MgATP2− + creatine (1)
While Golgi tendon organs (GTOs) feedback can be overridden by cognitive processes in the central nervous system (CNS), to allow an athlete to increase performance, it is likely that local peripheral systems can prevent the level of excess muscle contraction that could result in failure or damage
Summary
CK is a compact enzyme of around 82 kDa that is found in both the cytosol and mitochondria of tissues where energy demands are high. This shuttle system is critical for the production and maintenance of energy supply and is involved in the metabolic feedback regulation of respiration [5] It is unsurprising, that skeletal muscle has high levels of CK that can account for as much as 20% of the soluble sarcoplasmic protein in specific muscles. Raised levels of serum CK are still closely associated with cell damage, muscle cell disruption, or disease. These cellular disturbances can cause CK to leak from cells into blood serum [6]. There has been extensive discussion in the literature regarding the significance of raised levels of serum CK following physical exercise in relation to degrees of muscle cell damage or disturbance. We examine current evidence and opinion relating to the release of CK from skeletal muscle tissue into blood serum in response to muscle exercise
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