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Oral quercetin supplementation may blunt exercise-induced muscle adaptations (animal study).
Exercise induces the formation of reactive oxygen species (ROS), which, in excess, can promote muscle damage, fatigue, and immune dysfunction. However, ROS may also mediate beneficial training adaptations as a part of a biologically useful signaling cascade. A study from 2013 found that quercetin, a bioactive compound that exerts anti-inflammatory and antioxidant effects, blunts exercise induced skeletal muscle adaptations in rats.
Quercetin is both a direct and indirect antioxidant, meaning it scavenges ROS to prevent oxidative damage to DNA, proteins, and lipids and activates additional antioxidant enzymes. In the context of exercise, moderate levels of ROS can be beneficial because they can signal mitochondrial biogenesis.
The authors of the study exercised rats on a treadmill five days a week for six weeks. The rats received 25 milligrams of quercetin per kilogram of body weight or a placebo every other day and two hours before exercise. In humans, this dose is equivalent to about 2 milligrams per kilogram of body weight.
The authors found that quercetin supplementation blunted exercise-induced muscle adaptations in the rats. The combination of exercise and quercetin supplementation reduced mitochondrial content and increased protein carbonyl content, a marker of oxidative damage in the skeletal muscle. Quadricep muscle was collected from the rats and used to determine mitochondrial and protein carbonyl content.
These findings suggest that the antioxidant properties of quercetin decrease exercise produced ROS thereby blocking mitochondrial biogenesis. Additionally, the authors suggested that metabolites of quercetin may be influencing the production of oxidative damage.
Research in humans is needed to determine the degree to which quercetin may blunt exercise-induced adaptations, especially studies that investigate varying types of exercise in combination with quercetin along with the dose and timing of supplementation.
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