Repetitive muscle contractions during endurance and strenuous sports lead to increased production of free radicals such as reactive oxygen species (ROS), resulting in greater oxidative stress.

Because our cells’ adaptations to the different free radicals have evolved as important physiological regulatory signals, they can have both harmful and beneficial effects. A balance between oxidative stress and antioxidant defense (called redox balance) is therefore important to health and sports performance.

Many studies have shown that prolonged endurance sports and short, high-intensity exercise result in increased oxidative stress markers in blood and muscles. Increases of ROS can lead to a variety of adaptations in cells, depending on the location of ROS production, ROS concentration, duration of the cell’s exposure to ROS, and an individual’s training status.

Reactive oxygen and nitrogen oxides produced during muscle contraction are involved with several key adaptations to training, including mitochondrial biogenesis, antioxidant enzyme regulation, muscle hypertrophy (growth and enlargement of muscle cells), and glucose uptake by the skeletal muscles.

But when overproduction of free radicals overwhelms our body’s antioxidant defense system to neutralize them, cells and tissues, including muscles, can be damaged. Fatigue can set in, compromising exercise performance. Excess free radicals can also exert toxic effects such as oxidation of lipids and proteins, and DNA damage.

A single bout of exhaustive exercise can cause damage to the muscles and tissues of untrained individuals. But such damages are not observed in trained athletes whose resistance to oxidative stress is strengthened. In any event, exercise-induced oxidative damage is thought to be reversible with proper rest.

Once only thought of as toxic biochemical by-products in our body, ROS and other free radicals are now recognized as signaling molecules in a wide range of physiological processes.

During exercise, ROS are potent signaling molecules in the regulation of blood vessel dilation and, therefore, blood flow and distribution. Redox balance during endurance sports determines whether ROS promotes or impairs blood vessel dilution.

Blood flow is critical for sports performance because of increased muscle demands for oxygen and nutrients for energy, constant requirements of the brain, increased cardiovascular and respiratory demands, and increased demand of the skin to disperse heat and regulate body temperature.

To optimize sports performance, it is important to minimize muscle and tissue damage induced by free radicals, while maximizing the benefits of redox balance on blood vessel regulation.

Our GI tract is a key source of free radicals, and redox balance is critical to the nutrient digestion and absorption functions of the gut, gut wall cell proliferation, and immune response, among others.

Research connecting exercise, gut redox status, and gut microbiome is still in its infancy. But emerging evidence from both animal and human studies points toward a close relationship between them.

Furthermore, data suggest that gut microbiome regulates oxidative stress response and antioxidant enzyme activities, and that dysbiosis of gut microbiome promotes excessive oxidative stress and reduces exercise performance.

In particular, studies have shown that during chronic fatigue and intense or prolonged exercise, the activity of antioxidant enzymes becomes weaker, and that a balanced redox is linked to a balanced, healthy gut microbiome.

Researchers found that lower oxidative stress status is correlated with beneficial bacteria species Lactobacillus and Bifidobacterium, and excessive oxidative stress is correlated with the gut bacteria E. coli.

Taken together, study findings concluded that different gut microbiomes influence sports performance differently by modifying the activity of antioxidant enzymes, which affects exercise-induced fatigue.

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