A mixed 4x400 metres relay in which two men and two women will compete in a non-specific order was added to innovate the programme following the success of similar events earlier this year.

It was chosen in preference to a 4x100m relay because the difference in speeds between men and women in the shorter event was considered to make it difficult to conduct baton changes.

An International Olympic Committee (IOC) suggestion to consider a mixed relay in race-walking to replace the men's 50km walk was rejected.

"The IAAF is delighted that the IOC would like to include a mixed 4x400m relay in the athletics programme of the Tokyo 2020 Olympic Games," the world governing body said.

"This new discipline, tested earlier this year in Nitro Athletics and at the IAAF World Relays, has been hugely successful and appealing for athletes and spectators alike. 

"Pitching teams of two men and two women together with the added dimension of team tactics, make this a vibrant, youthful and exciting competition."

Athletics' quotas has been cut by 105 athletes in order to avoid exceeding the 10,500 upper ceiling in all sports at the Olympics.

The IAAF is "naturally disappointed" by this and will "review the qualification system and entry standards for athletics at the Olympic Games" in a way to find where to make cuts, they said.

They will seek to avoid cutting universality places for athletes from countries who would otherwise not be able to participate, but admitted that there would be an impact.

"Whilst we understand the need to be firm on numbers and applaud the IOC’s stance on gender equality in all sports, reducing the quota will inevitably have an impact on our joint goals of universality," the IAAF said in their statement. 

"There are 10 nations and most of the Refugee team who competed only in athletics at the Rio 2016 Olympic Games. 

"Just one of those nations met the qualification standards, the athletes from all the others - over 20 - were awarded wild cards."

IOC Sports Director Kit McConnell also claimed they would avoid countries missing out on obtaining universality places.

The IAAF also made it clear that the mixed relay will not consist only of athletes already appearing at the Games.

"We should not expect the athletes entered to compete in the men’s and women’s 4x400m relays, from which the participants for the mixed relay will be naturally drawn, to compete in a third round of heats and finals for the mixed relay without allocating the appropriate space and time in the programme or enabling teams to bring additional athletes," they said.

The addition of three new swimming events means that athletics is no longer the biggest sport on the programme.

There are now 49 medal events in aquatics, as opposed to 48 in athletics.

"Athletics is the number one sport at the Olympic Games so we want to work with the IOC to drive effective and meaningful change," said IAAF President Sebastian Coe after the announcement.

"We have agreed to look at the reduction in quota challenge to see what impact it will have on athletes and nations competing in athletics given that 10 countries compete only in our sport. 

"We will also work with the IOC on how best to introduce a mixed relay event in Tokyo following the huge success the Mixed Relay has enjoyed in IAAF World Relays and Nitro Athletics this year. 

"All proposals will go to the IAAF Council to review and approve at its council meeting ahead of the IAAF World Championships in London this August."