Archive for the 'Exercise Physiology' Category

Antioxidants and Exercise

Given the complexity of the human body it would be unwise to simply say that reactive oxygen species (ROS) are bad and antioxidants are good.  Metabolic by-products of muscle contractions, ROS cause lipid peroxidation and damage the protein machinery of cells, yet they have emerged as also being part of a complex biochemical signaling network in skeletal muscles.   Research such as Ristow et al. (2009) suggests that such species are necessary for exercise-induced adaptations since they are prevented by high doses of antioxidants.  Muscle function adaptations include contractile protein expression, angiogenesis and mitochondrial biogenesis, as well as increased insulin sensitivity which is one of the most clinically relevant effects of exercise.  The biochemical signaling pathways which are activated by exercise have also been shown to up-regulate antioxidant defence enzymes, such as superoxide dismutase, which defend against ROS.

Clinical trials of antioxidant supplements in disease prevention have generally been disappointing.  Whilst normal doses of antioxidants from the diet are required to support the defence system, Bouayed and Bohn (2010) suggest that adverse effects may result from the high doses that tend to be used in studies, by interfering with the crucial role that low levels of ROS has in many physiological functions.  Also such high doses of single antioxidant compounds may be toxic under certain conditions where other compounds that act in synergy are lacking, such as may be the case with the increased risk of lung cancers among smokers who take beta-carotene supplements.  It would interesting to see whether this increased risk is still there if beta-carotene is complemented by a range of other phytonutrients which could act in synergy.


Exercise, Opioid Peptides and Immune Function

Exercise, Opioid Peptides and Immune Function

The J-shaped curve  illustrates the relationship between the exercise and upper respiratory tract infections:

The graph suggests a protective effect of moderate exercise and that conversely, intense training or a marathon gives a window of opportunity for infection.  The varying infection risks appear to be due to changes in immune function, markers of which showing an inverse J-shaped curve.

The boost to natural immune function from moderate exercise lasts up to several hours, with an increased activity of natural killer (NK) cells, which inactivate viruses and reduce the potential of tumour cells to metastasise.  This process may help explain the protective effect of exercise against various cancers shown in epidemiological studies.

The activation of opioid pathways in response to physical exercise is well known, as is immunomodulation mediated by opioid peptides.  Jonsdottir (2000) describes how evidence has accumulated that the endogenous opioid system is part of the regulatory pathway between the central nervous system and the immune system, as well as giving suggestions for the role of central opioid receptors in mediating the enhanced natural immunity following chronic exercise.  These include via both direct nerve fibre connections with cells or organs of the immune system, as well as through neuroendocrine signalling such as via the hypothalamic–pituitary–adrenal axis.