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Antioxidants and Muscle Damage

Dr Alison Jenkinson

SR2002

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Outline• Mechanisms of muscle damage

• Protection against muscle damage: Interventions– antioxidants

– anti-inflammatory drugs– estrogens

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Suggested Mechanisms• Muscle weakness/Loss of force production

– inability to activate motor units by voluntary command

• however, this weakness is still seen following electrically stimulated muscle contractions

– depletion of metabolic substrates• however, loss of force production can be seen after

as few as 2 eccentric muscle contractions

– damage and degradation of contractile structures

• impairment of muscle contraction mechanisms

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Suggested Mechanisms• Soreness

– May be related to loss of cellular calcium homeostasis as a result of disrupted muscle contraction mechanisms and damage to sarcomeres

– Stimulates a number of pathways including an inflammatory/immune response

– Induces free radical production– These responses may be involved in causing muscle

tenderness in response to eccentric exercise

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Inflammatory Response• Within hours following muscle damage

neutrophils are chemically attracted to the area

• Increase in toxins including free radicals– increased membrane permeability and phagocytosis

of tissue debris

• Other immune cells such as monocytes attracted to the damaged area– formation of macrophages which also release free

radicals as part of phagocytosis of damaged tissue• required for activation of satellite cells and muscle repair

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Exercise and Free Radicals• Any species with one or more unpaired

electrons (includes the hydrogen atom, most transition metals and the O2 molecule)

• Free radicals may be produced endogenously through– normal oxygen metabolism (leakage from electron transport

chain)

– redistribution of blood flow - ischemia-reperfusion injury

– immune response - increase ROS production

– disruption of calcium homeostasis - activating ROS generation

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Free Radical Damage• Increased production of free radicals can disrupt

cell membranes and impair cell function– damage to lipids, proteins, DNA, cell membranes

• However, the body has a range of protective mechanism to defend against excess free radical production. These are known as antioxidants

• These antioxidants are produced within the body (endogenous) and are mainly enzymes orrequire to be consumed in the diet (exogenous)

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Antioxidants• Endogenous

– eg glutathione peroxidase, superoxide dismutase, catalase

• Exogenous– eg vitamin E, vitamin C, some carotenoids

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McBride et al (1998) Effect of resistance exercise on free radical production. Med.Sci.Sports Exerc. 30:1, 67-72

12 subjects, 50% received 1200IU vitamin E for 2 weeksbefore participation in ahigh intensity resistance exercise protocol

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McBride et al (1998) Effect of resistance exercise on free radical production. Med.Sci.Sports Exerc. 30:1, 67-72

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Cannon et al (1990) Acute phase response in exercise:interaction of age and vitamin E on neutrophils and muscle enzyme release. Am.J.Physiol 259, R1214-R1219

Subjects consumed either a placebo or vitamin E for 48d before completing a downhill running exercise protocol

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Anti-Inflammatory Drugs• The inflammatory process may be a cause of

DOMS• Therefore, it has been suggested that use of anti-

inflammatories (nonsteroidal anti-inflammatory drugs - NSAIDs) may be beneficial in reducing muscle damage and/or soreness

• Perception of muscle soreness may be reduced• Muscle function may be improved but results are

inconsistent• There does not appear to be any beneficial effect

on CK (it may even be increased)

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Estrogen

• There is some evidence to suggest that estrogen may influence the muscle cell membranes and lower the efflux of skeletal muscle enzymes such as CK

• Both animal and human studies suggest that estrogen may not protect against the amount of damage caused but may stabilise the tissue membranes and/or act as an antioxidant

• Some studies have suggested a reduction in muscle soreness and CK activity in females

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16From Kendall and Eston (2002) Exercise-induced muscle damage and the potential protective role of estrogen. Sports Med. 32:2, 103-123

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Summary

• There are mixed reports as to the whether antioxidants, estrogens and anti-inflammatory drugs may reduce muscle damage and DOMS

• Prior exercise, muscle damage and DOMS may be the best protection against damage from future exercise bouts

• DOMS and exercise induced muscle damage may be necessary for repair and adaptation