Exercise-induced muscle damage typically results in impaired performance, increased pain and soreness, and reduced training quality during the first 12–72 hours post-exercise, which can negatively impact athletes and active individuals who require rapid recovery between bouts of training or physical activity.

Muscle soreness or discomfort after exercise is referred to as delayed onset muscle soreness (DOMS), and is a common occurrence in individuals who engage in strenuous and/or unaccustomed exercise and physical activity. DOMS occurs as a result of exercise-induced micro-trauma to muscles and surrounding connective tissues. This trauma to the tissues subsequently triggers increased oxidative stress and the onset of an inflammatory response that is associated with the activation of leukocytes, muscle oedema, and several other intracellular events that aim to restore the integrity and function of the affected muscle.¹

A number of conditions, such as chronic inflammatory disorders and connective tissue damage, are associated with free radical damage.^2-4 It is well established that exercise increases reactive oxygen species and free radical production5, and it is thought that this excess production of free radicals may delay or prevent adequate muscle healing following intense exercise.⁶

Flavonoids such as quercetin are believed to act as health-promoting substances due to their antioxidant and anti-inflammatory properties. Quercetin is commonly found in several fruits and vegetables, especially onions, cruciferous vegetables, berries, citrus fruits and apples.^7,8 Dietary antioxidants such as quercetin may counteract oxidative stress by reducing the concentration of free radicals and reactive oxygen species associated with exercise, thus reducing DOMS.⁹

A recent randomised, double-blind, crossover design study investigated the use of quercetin for the prevention of strength loss and neuromuscular impairment associated with eccentric exercise-induced muscle damage (eccentric muscle action is characterised by the lengthening of skeletal muscle while producing force). Twelve healthy, moderately-active males (average age 26 years) ingested either quercetin (500mg twice daily) or placebo for 14 days and then crossed over to the opposite treatment after a 3-week washout period.  Participants completed a comprehensive neuromuscular evaluation before, during and after an eccentric protocol able to induce severe muscle damage (10 sets of 10 maximal lengthening contractions). Soreness, resting arm angle, arm circumference, plasma creatine kinase and lactate dehydrogenase were also assessed.¹⁰

At the end of the trial period, quercetin supplementation significantly increased the isometric strength recorded during maximal voluntary isometric contraction compared to baseline (+4.7%, p<0.05). Immediately after the eccentric exercise routine, isometric strength, the force–velocity relationship and muscle fibre conduction velocity were significantly lower in those taking placebo as compared to the quercetin group (p<0.05). Plasma creatine kinase and lactate dehydrogenase values were significantly greater in the placebo group post eccentric exercise compared to the quercetin group (p<0.05). These findings are in line with the hypothesis of quercetin’s role in protecting muscle fibres from damage.

The authors speculate that quercetin may have protected and stabilised membranes in the myocytes and preserved excitation–contraction coupling immediately post-exercise, an effect that may have reduced the muscle damage and attenuated the weakness immediately after exercise.

Although the efficacy of dietary antioxidant supplementation for physical exercise is continually being debated, these findings highlight the need for practitioners to consider quercetin as a suitable nutritional supplement for the support of muscle function and health, particularly in those patients just starting a new exercise regime or for those who are undertaking regular high intensity exercise.  Practitioners should consider the following supportive options:

• Prescribe between 1,000-1,500mg of quercetin per day in divided doses.
• Additional anti-inflammatory support is of particular importance for those patients with musculoskeletal injury and soft tissue inflammation. Consider a concentrated fish oil capsule with high EPA and DHA content and a herbal formula containing a highly bioavailable curcumin.
• Also consider other factors such as vitamin D levels and supplement as indicated. Vitamin D has important direct effects on skeletal muscle and supplementation has been shown to increase muscle strength, reduce injury rates and improve athletic performance.¹¹ Low levels of vitamin D may also be linked with higher levels of inflammatory markers.¹²
• Educate patients of the importance of consuming a diet rich in anti-inflammatory, antioxidant and nutrient dense whole-foods. Consumption of adequate dietary protein is also essential to support muscle repair and growth.

References

1. Jamurtas, A.Z., Exercise-Induced Muscle Damage and Oxidative Stress. Antioxidants, 2018. 7(4): p. 50.
2. Arulselvan, P., et al., Role of Antioxidants and Natural Products in Inflammation. Oxid Med Cell Longev, 2016. 2016: p. 5276130.
3. Mittal, M., et al., Reactive Oxygen Species in Inflammation and Tissue Injury. Antioxid Redox Signal., 2014. 20(7): p. 1126-1167.
4. Chen, L., et al., Inflammatory responses and inflammation-associated diseases in organs. Oncotarget, 2018. 9(6): p. 7204-7218.
5. Kawamura, T. and I. Muraoka, Exercise-Induced Oxidative Stress and the Effects of Antioxidant Intake from a Physiological Viewpoint. Antioxidants, 2018. 7(9): p. 119.
6. Kurahashi, T. and J. Fujii, Roles of Antioxidative Enzymes in Wound Healing. Int J Dev Biol, 2015. 3(2).
7. Kleemann, R., et al., Anti-inflammatory, anti-proliferative and anti-atherosclerotic effects of quercetin in human in vitro and in vivo models. Atherosclerosis, 2011. 218(1): p. 44-52.
8. Selamoglu, Z., Antioxidant Activity of Quercetin: A Mechanistic Review. Turkish Journal of Agriculture - Food Science and Technology, 2016. 4.
9. Simioni, C., et al., Oxidative stress: role of physical exercise and antioxidant nutraceuticals in adulthood and aging. Oncotarget, 2018. 9(24): p. 17181-17198.
10. Bazzucchi, I., et al., The Effects of Quercetin Supplementation on Eccentric Exercise-Induced Muscle Damage. Nutrients, 2019. 11(1): p. 205.
11. Abrams, G.D., D. Feldman, and M.R. Safran, Effects of Vitamin D on Skeletal Muscle and Athletic Performance. J Am Acad Orthop Surg, 2018. 26(8): p. 278-285.
12. Yin, K. and D.K. Agrawal, Vitamin D and inflammatory diseases. J Inflamm Res, 2014. 7: p. 69-87.

The information contained within is intended to be used as an educational tool and it is not intended to be used to diagnose, treat, cure or prevent any disease, nor should it be used for therapeutic purposes or as a substitute for your own health professional's advice.