Establishing the Effect of Long-term Orange Peel Extract Supplementation on Exercise Performance and Recovery

Rationale: Numerous studies have shown the positive effect of a healthy diet and regular moderate exercise. Although, exercise has also been correlated with an increase in reactive oxygen species (ROS) production and a higher incidence of injury. ROS production seems to induce muscle damage, which reduces muscle performance and induces fatigue. Increasing muscle recovery could be an effective way to increase exercise performance. Several food ingredients have been of growing interest due to their specific functioning on the human body. Citrus flavonoids are abundantly available in citrus fruits. Prior studies show a positive effect of citrus flavonoids on endothelial function, by promoting vasodilation. In addition it has a positive effect on the nitric oxide (NO) synthesis, a known compound in regulating endothelial response. This capacity of citrus flavonoids could be useful in stimulating performance and recovery after exercise. Additionally, the ability of scavenging ROS could reduce muscle damage caused by exercise induced oxidative damage.

Objective: Determine the 4-week effect of daily citrus flavonoid supplementation on exercise recovery and performance.

Study design: Randomized, double-blind, placebo-controlled study with parallel design, in which 40 subjects engage in three exercise sessions. The sessions will be subdivided into a pre-test and test 1 and 2. Between test 1 and 2, participants receive daily for 4 weeks citrus flavonoid supplement or a placebo. Each day, subjects should consume 2 capsules each morning, containing in total 500 mg of citrus flavonoids or 500 mg placebo.

Study population: The subjects will be healthy normal weight trained males, with an age of 18 - 25. Additionally, subjects are non-smokers and free of a medication.

Intervention: Participants will be randomly placed in either the citrus flavonoid or placebo group. Participants will be instructed to ingest 2 capsules each morning for 4 consecutive weeks. Each capsule equals to 250 mg of citrus flavonoids or cellulose in case of the placebo treatment.

Main study parameters/endpoints: The main study parameter is the average amount of work load produced during the 10-minute time trail test. In addition, oxygen per minute will be determined as well as the heart rate. Finally, for each test, the subjective rating of perceived exertion (RPE) will be determined during the pre-test and test 1 and 2 by using a Borg scale.