Hernandez started gymnastics in 2005. She became a Level 4 gymnast by 2008, and qualified for elite by 2012.
Hernandez's national debut came at the American Classic, where she tied for second on balance beam, placed sixth on floor exercise, and eighth in the all-around and on balance beam. She then competed at the Secret US Classic, where she sixth on floor exercise and seventh on balance beam, qualifying herself to the Junior Visa Championships. At Championships, she placed twenty-first in the all-around, nineteenth on vault and uneven bars, tied for twenty-first on balance beam, and tied for seventeenth on floor exercise. She wasn't added to the Junior National team, but she was invited to a National team training camp.
In February, Hernandez competed at the WOGA Classic, where she placed second in the all-around and third on uneven bars. In June, Hernandez competed at the Parkettes National Elite Qualifier for some extra competition experience, and won the all-around.
In early July, Hernandez was added to the National team. She then competed at the American Classic, placing first on floor exercise, second in the all-around (behind teammate Ariana Agrapides), third on vault and beam, and seventh on bars. At the US Classic, she won the floor exercise and placed sixth in the all-around.
At the National Championships in August, she won silver in the all-around, on uneven bars, and floor exercise, bronze on beam and also placed fifth on vault.
Shortly after Nationals, it was announced that Hernandez (along with compatriot Bailie Key) would compete at the Japan Junior International in September, marking her international debut. There she won bronze in the all-around and on vault, placed fourth on floor and sixth on balance beam. In November, she was announced as a competitor for the Mexico Open. She won gold with her team and silver in the all-around behind Key.
Hernandez injured her wrist training on balance beam and missed international meets in the spring. She pushed for the US Classic and National Championships, but injured her knee at a National Team training camp in June and needed surgery, keeping her out of competition for the rest of the year. She was cleared to train again in early November. In December, she verbally committed to the University of Florida.
At the January National Team training camp, Hernandez came in first in the junior all-around (third out of the juniors and seniors combined) and first in physical abilities. Her performance at camp won her a spot back on the National Team. Her return to competition came at the City of Jesolo Trophy, where she won team, all-around, uneven bars, and floor exercise gold. In July, she competed at the U.S. Classic, winning all-around, vault, and uneven bars gold, and balance beam and floor exercise bronze.
In August, she competed at Junior Nationals, winning the all-around title, as well as the uneven bars title, a silver on floor, and bronze on vault and beam. She was sent to compete at the Japan Junior International in September. She won all-around, vault, and floor exercise gold, and uneven bars and balance beam silver.
Hernandez made her senior international debut, winning team and balance beam gold, vault silver, and all-around bronze at the City of Jesolo Trophy. In April, she competed at the Pacific Rim Championships. She helped Team USA win gold but was edged out of the all-around by teammate Aly Raisman. In June, she only competed on uneven bars, where she placed fourth.
At the National Championships, she won all-around, uneven bars, balance beam, and floor exercise bronze. She advanced to the Olympic Trials, where she placed first on balance beam, second in the all-around, third on floor exercise, fourth on vault, and seventh on uneven bars. Her performance on both days brought about loud cheers from the crowd, culminating in the crowd cheering her name after she closed the second day of competition on balance beam. She was named to the U.S. Olympic Team.
Just prior to podium training, Hernandez went pro, forfeiting her NCAA eligibility.
The Americans competed in the fourth subdivision of qualifications, starting on floor exercise. Hernandez only competed on three events, sitting out the uneven bars, but nonetheless she helped the Americans qualify first to the team final. Individually, she qualified second to the balance beam final. She continued to compete on three events in the team final, helping secure the gold for the Americans. The team named themselves the "Final Five". In the balance beam final, she delivered a solid routine that won her the silver medal behind the Netherlands' Sanne Wevers.
Hernandez took part in the Kellogg's Tour of Gymnastics Champions. Alongside that, she also competed in the twenty-third season of Dancing With the Stars, paired with professional dancer Val Chmerkovsky. She was crowned the winner on November 22, 2016, making her the youngest winner in the show's history. Following her win, she joined the show's professional dancers on the Dancing With the Stars Live! Tour from December 2016 to February 2017.
Hernandez resumed training in late 2017, training briefly at Precision Gymnastics. In June 2018, she made the move to California to train at Gym-Max Gymnastics under Jenny Zhang and Howie Liang.
|2012||Junior American Classic||8||2nd||6|
|Junior Secret U.S. Classic||7||6|
|Junior Visa Championships||21||19||19||21||17|
|Parkettes National Elite Qualifier||1st|
|Junior American Classic||2nd||3rd||7||3rd||1st|
|Junior U.S. Classic||6||8||8||16||1st|
|Junior U.S. National Championships||2nd||5||2nd||3rd||2nd|
|Japan Junior International||3rd||3rd||6||4|
|2015||City of Jesolo Trophy||1st||1st||1st||1st|
|Junior U.S. National Championships||1st||3rd||1st||3rd||2nd|
|Japan Junior International||1st||1st||2nd||2nd||1st|
|2016||City of Jesolo Trophy||1st||3rd||2nd||1st|
|Pacific Rim Championships||1st|
|St. Louis U.S. National Championships||3rd||3rd||3rd||3rd|
|U.S. Olympic Trials||2nd||4||7||1st||3rd|
|Rio de Janeiro Olympic Games||1st||2nd|
2015-2016 - "Skeletons" by Drehz