When American tennis player Frances Tiafoe said pickle juice had helped him reach the quarter-finals of the Australian Open, plenty of people were a little taken aback/grossed out.

After all, who swigs the remnants of a jar of pickles to boost their sporting performance?

More people than you might think, actually.

Taking the Australian Open in isolation, two of the sport’s rising stars – Tiafoe, 21, and Russia’s Daniil Medvedev, 22 – have been spotted drinking it in Melbourne this week.

And widening the sample size a little, a photographer snapped Arsenal’s 22-year-old Uruguay midfielder Lucas Torreira drinking from a bottle labelled “pickle juice” in the Gunners’ 2-0 victory over Chelsea last weekend (although he did swiftly spit it out!).

Is this sport’s latest fad? And what is the science behind it all? BBC Sport finds out.

Tiafoe’s not-so-secret weapon

Unseeded Tiafoe was a surprise quarter-finalist in the Australian Open, and made further headlines with his choice of replenishment following that win over Bulgaria’s Grigor Dimitrov in the last 16.

Speaking about the gruelling four-set match, which lasted three hours and 39 minutes in the Melbourne heat, Tiafoe said: “I had the break, but started to feel my body.

“He played a good game to break me. After that, as you asked me, I was trying to stay alive. I was downing pickle juice, having that like Kool-Aid, just trying to get that done.

“I’m talking straight up: just downing it. It tasted terrible. I’m feeling terrible right now, man.”

The following day, Medvedev took time out from his match against Novak Djokovic to down some of the pungent fluid.

John Millman, the 2018 US Open quarter-finalist, was commentating on that match for television and was asked about the pickle juice.

“It helps the cramps,” said Millman. “There’s a lot of salt in it.”

When asked how it tasted, the Australian replied: “Terrible.”

It tastes bad… but does it actually work?

In a word: Yes.

Dr Mayur Ranchordas – a senior lecturer in sport nutrition and exercise metabolism at Sheffield Hallam University – has used the technique with professional cyclists and Premier League footballers.

And while, he says, the results are compelling, it is not necessarily for the reasons you might initially expect.

“Pickle juice contains sodium, potassium and vinegar and the obvious conclusion would be that it replaces sodium and salts lost when playing sport in a hot and humid environment like the Australian Open thus prevent cramping,” said Dr Ranchordas.

“However, how it really works is that it triggers a reflex in the mouth which sends a signal to stop muscles from cramping. That’s why it is drank at the onset of cramp.

“It stops cramping 40% faster than drinking water.”

Dr Ranchordas says it is particularly effective as a treatment for cramps in warmer conditions or when sporting occasions last longer than anticipated – be it a five-set tennis match or in extra time of a football game.

Just last month, India batsman Cheteshwar Pujara was shown grimacing on TV as he took the foul-tasting fluid on board during a marathon innings in oppressive heat in Adelaide.

What else is it good for?

The internet is full of stories of how pickle juice can cure alcohol-induced hangovers. One website even suggests pickle brine is the definitive hangover cure in some eastern European countries.

Throw in the fact it contains antioxidants, is said to help control blood sugar levels and boost gut health and you’re on to a winner next time you reach for a nice refreshing glass of the stuff.

And the craziest thing of all?

It is actually good for your breath, because it kills bacteria which breed in your mouth and create a stink.

Now you’re convinced, right?

Second seed Rafael Nadal eased past unseeded American Frances Tiafoe to reach the Australian Open semi-finals and continue his bid to win all four Grand Slams for a second time.

The 32-year-old Spaniard cracked 29 winners in a 6-3 6-4 6-2 victory.

Nadal broke 21-year-old Tiafoe in each of his first service games of the set.

The 17-time Grand Slam champion will play Stefanos Tsitsipas in the last four after the 20-year-old Greek beat Spain’s Roberto Bautista Agut.

“It is emotional to be back in the semi-finals,” said Nadal, who retired injured in his quarter-final against Marin Cilic last year.

“I had some troubles in this event so, after a while of not playing, to be back in the semi-final means a lot to me. I feel very lucky to be where I am after all the troubles I’ve been through.”

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Nadal dominates next generation

Nadal, who did have to stave off two break points at 2-1 in the second set, has not dropped a set as he aims to become the first man to win each of the four Grand Slams twice in the Open era.

Despite reaching at least the quarter-finals in 11 of his past 12 appearances, including four finals, he has only converted one of these runs into victory – his sole triumph at Melbourne Park in 2009.

And, despite not playing competitively since September’s US Open because of multiple injuries, he has cruised through his opening five matches.

Tiafoe, who celebrated his 21st birthday by reaching his maiden Grand Slam quarter-final on Sunday, could not cope with Nadal’s quality and intensity.

He had spent almost 12 hours on court coming into the match – more than three hours longer than Nadal – including his four-set wins over Wimbledon finalist Kevin Anderson and former world number three Grigor Dimitrov.

Nadal broke again for a 5-2 lead in the third, going on to serve out victory in one hour and 47 minutes.

The Spaniard used his trademark forehand to great effect, particularly down the line, hitting 13 winners on that side.

“The serve and winner with the first forehand is something very important for me, very important today, but also very important if I want to keep playing for a few years,” he said.

“It has given me a lot of free points and that is so important at this stage of my career.”

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Tsitsipas, 20, followed his last-16 victory over defending champion Roger Federer with another four-set win over Spain’s Roberto Bautista Agut earlier on Tuesday.

Nadal has beaten the Greek in straight sets in both of their previous meetings – in ATP finals on clay in Barcelona and the Toronto hard-court last year.

“It is going to be a great year to be sharing generations, that’s what makes this sport special – let’s see what happens,” Nadal said.

“During the last year he has been improving every month. He has already won a tournament and now in the semi-finals and able to win against best players in the world.

“He is unbelievable today but he has the chance to be one of the best for a long time.”

Danielle Collins has reached the Australian Open semi-finals, having never won a Grand Slam main draw singles match prior to the tournament.

The American, 25, beat unseeded Russian Anastasia Pavlyuchenkova 2-6 7-5 6-1 in two hours and 16 minutes in Melbourne.

Collins broke twice in the second set and won seven games in a row as she raced through the decider.

The world number 35 faces two-time Wimbledon champion Petra Kvitova or 15th seed Ashleigh Barty next.

“It was my first time playing on Rod Laver and I didn’t even practise on here before so it was quite the experience,” said Collins. “I absolutely loved it.”

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It was a feisty match from the start as the opening two games lasted 22 minutes and saw seven break points – including five which Collins could not take.

Collins, who knocked out world number two Angelique Kerber in the fourth round for the loss of just two games, was vocal throughout and showed plenty of emotion on court.

Pavlyuchenkova’s experience of four previous Grand Slam quarter-finals was evident in the first set as she remained calm and held off Collins’ early pressure.

The Russian, who beat 2017 US Open champion Sloane Stephens in a mammoth fourth-round tie that went on until 01:53 local time, fought back from 5-2 down in the second set to 5-5. But she had the stuffing knocked out of her when Collins broke again to level the match.

The American was full of momentum and went on to break twice in the final set, while Pavlyuchenkova won only nine points on her serve in the decider.

Collins could not convert a match point at 5-0 and was made to work in her last service game before she eventually secured victory on her third match point.