Andy Murray waits for test results as he tries to solve cramping issues ahead of US Open

With three days to go before the start of the US Open, Andy Murray is sweating on his test results.

When he left Wimbledon, beaten in the second round by John Isner, he made it his task to haul his ranking – then No 52 in the world – up into the world’s top 32 to secure himself a seeding for the last grand slam event of the year. But in the four tournaments he has played, he has won just three matches – a poor return due in no small part to regular bouts of cramp. This week, he is No 49 in the world order.

At the age of 35 and with nearly two decades as a professional behind him, this new problem comes as a perplexing surprise. He did suffer from cramp in his very early days when, as a young and spindly teenager, the combination of the excitement and tension of playing his first matches in the spotlight – and doing so against older, stronger men – would cause his muscles to seize. But those days are long behind him.

“No one knows exactly why people get cramps,” Murray said on Wednesday in Manhattan. “Some people think it can be hydration related, conditioning related, stress related, whether you’ve not eaten the right stuff – there can be a number of factors that go into it. It could be an underlying illness. And we’re just trying to get some answers to that.

“I’m doing sweat testing today in these conditions to see if anything has changed in that respect because the sports drinks and electrolytes that I drink, they are made specifically based on my sweat tests. But I haven’t done sweat testing for quite a number of years.

“If it was purely from hydration, let’s say, then obviously after I got cramp in Washington, I made sure that I was not dehydrated going into the next matches. If it was eating related, I made sure all