In this study, researchers are learning more about RTA 408, also known as omaveloxolone, BIIB141, or SKYCLARYS®. The main goal of this study is to learn more about the safety of RTA 408 and how it affects physical effort, movement, coordination, and how participants feel in daily life. The main questions researchers want to answer in this study are: * How much physical effort can a participant produce during a cycling test after 12 weeks of treatment? * How do scores on the modified Friedreich's Ataxia Rating Scale (mFARS) change after 48 weeks? Researchers will use the modified Friedreich's Ataxia Rating Scale (mFARS) to measure how FA affects the nervous system. The mFARS looks at movement ability, balance, coordination, speech, and how well the arms and legs work. They will also use a cycling test to measure physical effort, along with questionnaires to learn how participants feel and function in daily life. Safety will also be tested using physical exams, vital sign checks, echocardiograms (ECHO), electrocardiograms (ECG), and blood and urine tests. The study will be done in 2 main parts, followed by an optional Extension period: * In Part 1, participants will be randomly assigned to take different doses of RTA 408 or a placebo by mouth once a day for 12 weeks. A placebo looks like the study drug but contains no real medicine. * Researchers will compare these doses to decide which one to use in Part 2. * In Part 2, a different group of participants will take either the chosen dose of RTA 408 (150 mg) or placebo once a day for 48 weeks. * Participants who complete Part 1 or Part 2 may be able to join an Extension period, where everyone receives RTA 408. * In the Extension period, participants will continue to receive RTA 408 until the drug becomes commercially available or until they leave the study * Participants in Part 1 will have up to 9 study visits and 2 phone calls. If they do not move onto the Extension period, they will stay in the study for up to 20 weeks. * Participants in Part 2 will have up to 10 study visits and 3 phone calls. If they do not move onto the Extension period, they will stay in the study for up to 61 weeks. * Participants in the Extension period will have 2 visits in the first month, followed by visits every 6 months.
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Change From Baseline in Peak Work (in Watts/kg) During Exercise Testing at Week 12 in Part 1
Timeframe: Baseline through 12 weeks after participant receives the first dose in Part 1.
Change in the Modified Friedreich's Ataxia Rating Scale (mFARS) at Week 48 in Part 2
Timeframe: 48 weeks after participant receives the first dose in Part 2