JUDY Murray has called for a change in the rules to allow all tennis players to ask for heat breaks as Wimbledon experienced its hottest ever day.

A ball boy fainted on Court No 17 amid soaring temperatures of 35.7C with the sun out in full force and humidity also high.

While matches on the women's tour permit a 10-minute break between sets two and three in conditions in excess of 30C, there are no such guidelines for men other than individual cases such as the Australian Open, where the referee can suspend play or order a rest period.

John McEnroe, the three-time former Wimbledon champion, said there was a sexist element to denying men the same privileges afforded to women on tour and Ms Murray said the men's game should adopt the same rules.

She spoke of the "scary" moment when her older son Jamie suffered heatstroke playing in Australia and said men should be able to take breaks.

"You cannot mess with people's health," said Ms Murray. "I think the men should adopt it as well, especially because they have to play five sets.

"A slam is such a tough thing to play in, I know you get a day in between matches but if you're going to win a slam you need to play seven matches in 13 days.

"And for the men working across the best of five sets it's incredibly physically and mentally draining, so I think the men should take advantage of it as well."

Courtside readings when Murray played his first round match against Mikhail Kukushkin on Tuesday hit 41C and while the 28-year-old trains in extreme heat in Miami to prepare himself for such conditions, the Scottish complexion is not generally built for this environment.

His older brother Jamie suffered heatstroke at the Australian Open back in January 2014 and their mother said she felt powerless at the time.

"We are not known for our ability to cope with severe heat or sunshine - we do not get much of it," said Ms Murray. "Andy has been quite fortunate in Australia in that he has been put on the bigger courts, and the roofs can come across to provide some comfort from the sunshine.

"But I watched Jamie play a doubles match in Australia and he had heatstroke after it. He was four hours in the locker room just shaking and that was really, really worrying because he was afraid.

"And I couldn't go in the locker room so I had to phone Andy and say 'come, Jamie is in trouble and you need to be with him'. So he rushed from his hotel and hung out with him and the doctor.

"But that is really scary because you don't really know what is happening. Your body loses its ability to cool down."

She added: "You need to take the advice of doctors and sports scientists as to what that they [the changes] should be. At what point do you stop a match and at what point do you stop a match from going on? And do you allow them to take breaks to re-hydrate or re-charge or whatever it is.

"It is not for me to say but there are people who will study that and know what the change should be."

Women's Tennis Association rules state that when air temperature, humidity and surface temperature reach above 30C, players can ask for scheduled breaks. But the men's tour, run by the Association of Tennis Professionals, has no such rule.

McEnroe described it as "reverse sexism".

He told ESPN: "The tournament directors rule the ATP too much in my opinion. The players should rule it, as they should rule Wimbledon and the other majors."

Under the WTA, heat readings are taken 30 minutes before play begins, then again at 2pm and 5pm, and the rule is applied on a case-by-case basis before matches begin.

Wimbledon referee Andrew Jarrett said on Tuesday the WTA heat rule had been implemented twice before at SW19, in 2006 and 2009.

The Australian Open upholds a separate extreme heat policy, when the mercury moves past 40C.

The ball boy who collapsed during the match between Australian Matthew Ebden and American John Isner was taken to hospital.

Afterwards, an All England Club spokesman said: ''He's sitting up and is conversant but has been sent to hospital for a precautionary check-up.''