Endurance cyclist Mark Beaumont is expected to arrive in Paris on Monday 18 September, 79 days after setting off on his attempt to cycle around the world in 80 days.

The Guardian joined Beaumont in Lisbon on Wednesday, where he arrived on an overnight flight from Halifax in Canada to start the final leg of his record-breaking challenge. Despite cycling an average of 240 miles over 16 hours every day since 2 July, he looked fresh and sounded upbeat as we ticked off more miles on our way to the Spanish border. Yet he admitted the ride has taken its toll on him, both mentally and physically.

“I’ve been to some very low places and it’s reduced me to tears on four occasions, which has never happened on any of my other expeditions,” said Beaumont, who started his long-distance cycling exploits at the age of 11 when he rode 145 miles across Scotland.

“It’s taken me to some strange places mentally,” he said. “I didn’t want to have any excuses to fail, that’s why I made the rule that I would ride four blocks of four hours every day without any breaks during them. It makes life a lot simpler when you don’t have any exit doors like that.”

Barring disaster, Beaumont will smash the previous record of 123 days set by New Zealander Andrew Nicholson, but still grapples with doubts about how he is viewed by the “mainstream cycling” fraternity.

“I’m still not sure it has accepted me,” he says. “I know that my main fanbase is 40-year-old males in lycra and that’s great, but I still get complaints that I’ve sold out with all my corporate sponsorship, or that I’m not doing it in the proper spirit because I’ve got two support vehicles and am racing through at 240 miles a day.

“But when I originally cycled around the world unsupported 10 years ago [setting a then-record of 194 days], I described myself as an adventurer. These days I’m an athlete. It’s all about the performance, it’s about making a livelihood from what I do and being able to support my family, just like Chris Froome makes his living from cycling. Yet he couldn’t do what I’m doing, and I couldn’t do what he does.”

Beaumont’s support team has varied from continent to continent, but the key figures have been team leader and Falklands veteran Mike Griffiths, performance director and trans-Pacific rower Laura Penhaul, and mechanic/navigator Alex Glasgow, a veteran of unsupported cycle trips around the world.

Penhaul had sent detailed instructions about personal hygiene in advance of the Guardian’s arrival, not wanting to risk exposing Beaumont to any infections while his immune system is vulnerable. She takes daily swabs of saliva to monitor his health.

At one point Penhaul handed the Guardian a couple of paracetamol, saying: “Can you give these to Mark – he’s suffering a bit. His body is going into recovery mode.”

Upon catching up with Beaumont, who rides each day at a steady 15mph, he said: “My whole body has been protesting since I got off the plane, especially the pressure points on my hands and feet. Laura had to dig out a callus on my foot in Canada. She also had to replace the filling in my tooth [the consequence of a crash in Moscow], and I’m so tired that I fell asleep while she was doing it.”

While Penhaul has been overseeing Beaumont’s physical and mental welfare, with duties ranging from nutritionist and masseur to GP and counsellor – Griffiths and Glasgow have been constantly fine-tuning the route so that it satisfies Guinness World Records requirements.

“It’s been an emotional rollercoaster, a living, breathing project that has constantly flexed its muscles,” says Griffiths. “We keep revising the route so that we’ll hit the target of 18,000 miles without any waste. It’s alright to say, ‘Put in a fudge factor’, but it’s Mark who has to ride it. When he rode around the world last time he added an extra 300 miles just to be safe. Well, he can’t do that in 80 days.”

Fuel stop: Beaumont has to consume about 9,000 calories a day. Photograph: Courtesy of Trevor Ward

As of Wednesday, the team’s projected mileage total was eight miles short – so Griffiths improvised a detour to make up the shortfall.

At one point during the ride, Beaumont’s phone buzzes. It’s Nicci, his wife and mother of their young daughters, Harriet and Willa, who he hasn’t seen since 2 July. “She told me she’s coming out to Paris on Sunday,” says Beaumont, before adding: “That suddenly sounds very close.”

His next big challenge will be resuming “a normal, family life”. After living a daily routine defined by numbers – 16 hours cycling, 9,000 calories consumed, five hours of sleep – his team have prepared an extensive “decompression” strategy.

“I’ve done very little walking during the past 75 days. I walked up some stairs at the airport and it really hurt. But I’m looking forward to getting on my bike without any targets or deadlines.”

He also fully expects others to have a go at his record.

“I sincerely wish them well,” he said. “There’s no reason it couldn’t be broken. After all, I’m hardly your typical cyclist – I’m 6’3” and 90 kilos. Someone who is 75 kilos and a ‘proper’ cyclist might do it faster. We shall see.

“But I’ll always be the first who did it [in under 80 days]. No one remembers who was second up Everest.”

• Mark Beaumont is an ambassador for Visit Scotland. Trevor Ward’s bicycle was provided by Cycling Rentals in Lisbon.