Miyata began training in gymnastics when she was four years old after following her older brother to a gymnastics class.[2]
Junior
Miyata made her international debut at the 2018 International Gymnix competition in Montreal where she placed tenth in the all-around. In the event finals, she placed fifth on the vault and seventh on the balance beam.[3] Later that year, she competed at the Junior Asian Championships where she helped Japan finish second in the team competition behind China. Individually, Miyata won bronze on vault behind Qi Qi of China and compatriot Ayumi Niiyama.[4]
Miyata finished 28th in the all-around during the qualification round of the 2019 All-Japan Championships.[5] She was selected to represent Japan at the inaugural Junior World Championships alongside Hazuki Watanabe and Chiaki Hatakeda. Together, they finished 11th as a team.[6] Individually, Miyata finished 18th in the all-around and was the highest-placing Japanese female gymnast,[7] and she was the first reserve for the vault final.[8] She then placed 23rd in the all-around at the 2019 All-Japan Junior Championships.[9]
Miyata became age-eligible for senior international competitions in 2020 and made her senior international debut at the Melbourne World Cup. She finished third on vault behind Jade Carey and Coline Devillard.[10] However, most other competitions were canceled or postponed due to the global COVID-19 pandemic. In September, she competed at the All-Japan Senior Championships and finished 10th in the all-around.[11] Then in December, she placed 56th in the qualification round of the All-Japan Championships.[12]
2021
Miyata finished 36th in the all-around during the qualification round of the All-Japan Championships.[13] She then won a silver medal on the vault behind Mai Murakami at the All-Japan Event Championships.[14] At the All-Japan Senior Championships, she won the all-around title and improved her score from the All-Japan Championships by over 5 points.[15] She led her club to the bronze medal at the All-Japan Team Championships and had the highest score in the all-around.[16]
2022
Miyata began the season with a second-place finish at the All-Japan Championships.[17] She then won the all-around title at the NHK Trophy, becoming the first high schooler to win the women's event in seven years.[18] At the Asian Championships, she helped Japan finish third as a team. Individually, she placed fourth in the all-around and won silver medals on the vault and floor exercise behind Yeo Seo-jeong and Wu Ran, respectively.[19]
In late October, Miyata made her senior World Championships debut at the World Championships in Liverpool, qualifying for the all-around, vault, balance beam, and floor event finals.[20] She contributed scores of 14.400 on vault, 13.233 on balance beam, and 13.700 on the floor exercise towards Japan's seventh place finish in the team final.[21] She then finished eighth in the all-around final,[22] fifth in the vault final, and eighth in the floor final.[23] In the balance beam final, she scored 13.533 and won the bronze medal behind teammate Hazuki Watanabe and Canadian Ellie Black.[24] After the World Championships, she led her team to the title at the All-Japan Team Championships.[25]
2023
In April, Miyata graduated from high school and enrolled in Juntendo University and joined its gymnastics club.[18] She competed at the All-Japan Championships despite a stress fracture in her right heel, and she finished second behind Hazuki Watanabe.[26] She then won her second consecutive NHK Trophy title and was selected for the World Championships team.[27] She won the vault title at the All-Japan Event Championships and placed seventh on the balance beam.[28]
Miyata competed at the World University Games where she helped Japan finish second as a team behind China. She withdrew from the all-around final after the third rotation, but she still competed in the event finals. She won gold on vault, bronze on floor exercise, and placed fourth on balance beam.[29] At the 2023 World Championships in Antwerp she helped Japan qualify for the team final, where they ended up in eighth place and secured an Olympic berth.[30] Individually she qualified for the vault final, where she placed sixth.[31] After the World Championships, she competed at the All-Japan Team Championships and helped her club place seventh.[32]
2024
Miyata began the season with her first All-Japan Championships victory.[33] In the lead up to the NHK Trophy, she injured her left groin, but still chose to compete.[34] She won the gold medal in the all-around and was selected for the Japanese Olympic team alongside Rina Kishi, Haruka Nakamura, Mana Okamura, and Kohane Ushioku.[35]
Miyata was forced to leave the Olympic team before the start of the Paris Games after allegations surfaced that she had been smoking, in violation of the team's conduct code.[36] On 19 July 2024 the Japan Gymnastics Association announced that Miyata had admitted to smoking and drinking, and would be withdrawing from the Games.[1][37] She was 19 at the time, which is under Japan's legal smoking and drinking age of 20.[1] In December 2024 the association announced that Miyata would not face any penalties, saying that her decision to withdraw from the Olympics was punishment enough.[38]
^ ab"体操女子の新エース・宮田笙子、4月から順大に進学「体操だけでなく人間力も高めていけるよう」" [New female gymnast Shoko Miyata to enter Juntendo University in April "so I can improve not only my gymnastics skills but also my humanity"]. Sports Hochi (in Japanese). 22 February 2023. Retrieved 23 May 2024.
^Ogawa, Kanta (3 May 2023). "全日本選手権2位で流した涙のワケ 体操女子エース宮田笙子" [The reason behind the tears shed by female gymnast Shoko Miyata after coming in second at the All Japan Championships]. Sankei Shimbun. Retrieved 23 May 2024.
^"宮田笙子がNHK杯2連覇 2月右かかと疲労骨折のエースが意地の逆転 2位岸、3位深沢、4位渡部までが世界選手権代表に内定" [Shoko Miyata wins the NHK Trophy for the second consecutive year. The ace who suffered a stress fracture in her right heel in February made a determined comeback. 2nd place Kishi, 3rd place Fukazawa, and 4th place Watanabe have been selected to represent Japan at the World Championships.]. Daily Sports (in Japanese). 20 May 2023. Retrieved 23 May 2024.
^"体操日本女子がパリ五輪出場権 世界選手権で予選8位" [Japanese gymnastics girls qualify for Paris Olympics, 8th place in qualifying at world championships]. Nihon Keizai Shimbun (in Japanese). 3 October 2023. Retrieved 19 May 2024.