The aim of this project is to investigate the effects of riboflavin, also known as vitamin B2, on preventing delayed onset muscle soreness (DOMS) in ultramarathon athletes through a randomized placebo-controlled study.

The riboflavin 100 mg capsules will be self-dosed by the participant, one capsule prior to the long stage of the race followed by a second dose at the end of the long stage. Historically, long-stage finish times have ranged between 8 and 24 hours. The placebo will also be dosed as one capsule on the morning of the long stage, prior to the race start, and one capsule at the end of the long stage.

Inclusion Criteria:

1. Provision of signed and dated informed consent form
2. Stated willingness to comply with all study procedures and availability for the duration of the study
3. Male or female, aged 18 or over
4. In good general health as evidenced by readiness to participate in an ultramarathon
5. Ability to take oral medication and be willing to adhere to the study regimen
6. For females of reproductive potential: use of highly effective contraception for at least 1 month prior to screening.

Exclusion Criteria:

1. Unable to read or understand English
2. Under 18 years of age
3. Pregnancy or lactation
4. Known allergic reactions to components of the investigational drugs

Subjects will be masked to which intervention they receive, active study drug or placebo.