'I rode 900 kilometres on one leg': One rider's search for a new crank in the Mexican deserts

If you've never tried one-legged drills on the bike, you're missing out. It's an exquisite kind of fatigue that quickly makes you realise that two legs working together add up to way more than the sum of their parts.

Such exercises can help balance out leg strength and help aid pedalling fluidity, so they say. The idea, of course, is to ensure you do the same amount on each leg – 30 seconds left, 30 seconds right, you get the idea.

What you definitely do not do is to emulate ultra-cyclist and motivational speaker James Benson-King. He rode 900km through Mexico on one leg after his crank fell off in the middle of nowhere.

It happened during a ride from tip-to-tip – the northernmost road in Alaska, all the way down to the southern tip of Argentina. He was getting on for halfway, having just entered Baja California in Mexico, when his left-hand crank began to slip.

"I was in the middle of the desert at the time," he tells Cycling Weekly. "As I was riding along, there'd been a bit of a wobble on my pedal, but I'd been kind of ignoring it. And all of a sudden my entire left crank just fell off – still clipped in."

Benson-King had vowed at the start of the ride – which he used to raise money for the Cardiac Risk in the Young charity – that he would pedal every kilometre, so hitching a lift was not an option. Instead, he pushed on using one leg, 40 kilometres to the next town where – you guessed it – "there wasn't a bike shop in sight".

Eventually he managed to shim out the spindle with slices of Coke can and tighten it up extra-hard with new bolts.

"I thought, you know, this is a killer fix," he smiles. "So I went off to test it, clipped in, put the tiniest bit of pressure on the pedal and the thing span around again."

With the inside of the crank essentially rounded out, that's when he realised it was going to be a fairly major problem, for the next town was 100 miles away.

"Fortunately it was flat. I think otherwise I'd be ruined," he said. "But yeah, the minute I hit any climb, was significantly slower."

Predictably there was no bike shop in that town – or the one after that.

"I just kept going," he says.

He finally managed to replace the offending crank after meeting up with friends for Christmas at Todos Santos at the southern tip of Baja California. He'd had a shipment sent down by some other friends, but not before his right leg had done some serious bulking out in comparison to the left. It didn't go unnoticed.

"My friends were all laughing because my right leg was just, yeah, hench," he laughs, "and the left one had dwindled."

And much as one-legged drills should always be balanced between left and right, it will come as no surprise that Benson-King did not repeat with the left.

He ultimately raised more than £11,000 for CRY with the 20,000-mile (32,000 kilometres) ride, and is planning more endeavours for next year when he will attempt to become the first person to cycle across Antartica.