Jessica Ennis-Hill called for more to be done to encourage the nation's young people, particularly girls, to play sport as a means of boosting their confidence, health and wellbeing.
Meanwhile, a new YouGov study for Sky Academy of over 1,600 young people and 600 parents across the country shows girls have less confidence than boys in almost all situations, apart from online when using social media.
Ennis-Hill was leading a Sky Academy Confidence Day in Sheffield, which aims to develop young people's confidence through the power of sport. The day is part of Sky Academy's Confidence Month and is showcasing the Sky Sports Living for Sport initiative that works with sports stars, schools and teachers across the country to build practical skills like teamwork, planning, resilience and communication. Over 300 young people aged 11-18 tried new sporting activities to help build their confidence.
Over two thirds (66%) of girls say their confidence is influenced by how attractive or unattractive they feel, compared to just 46% of boys; and over half of girls (51%) say the clothes they wear affects their confidence whilst this impacts only a third of boys (36%).
Figures also revealed that girls' confidence is often hit when dealing with new and unfamiliar experiences, as more than half of girls (54%) say they feel unconfident when trying something they have not done before, compared with 41% boys. While 61% of girls struggle with confidence when starting a first day at school, college or a job, compared to only 46% of boys.
With both appearance and trying new and unfamiliar experiences impacting girls' confidence, it is not surprising that girls' participation in sport falls in their teens with 92% of girls aged 13-15 not meeting the minimum requirements for physical activity compared to 86% of boys.
Sky Academy Ambassador, Jessica Ennis-Hill, said: "Confidence has played a big part in my success as an athlete. The enjoyment, focus and determination sport gave me as a young person was a huge part of developing my confidence and self-belief as I grew up.
"I am passionate about young people, particularly girls, taking part in sport and I am delighted to be part of Sky Academy's Confidence Day. Sport can improve health, wellbeing and confidence while also teaching valuable life skills."
Youth Sport Trust Chief Executive, Ali Oliver, comments: "Sport and physical activity improve confidence, increase attainment at school and create healthy habits that last a lifetime.
"This research demonstrates the worrying and stark reality of the issues faced by young people today. Initiatives such as Sky Sports Living For Sport, a programme developed and delivered by the Youth Sport Trust, give young people the confidence and belief they need to be more active.
"We are proud to work with and be part of Sky Academy's Confidence Day, and are delighted to see so many young people enjoying the event."
Annette Du Bois, child confidence expert, comments: "Sport can have huge benefits for girls of all ages, particularly when it comes to improving body confidence, fitness and general wellbeing. Modern society puts a wide range of pressures on young people to look a certain way and appear confident. However, we know inner confidence is something that a lot of young people struggle with, so encouraging young people to be active, play sport and be part of a team will help their development and build resilience."