Sydney NSW, Australia, 30 December 2015 | AAP

Lleyton Hewitt’s unprecedented 20th straight Australian Open tilt next month will be the culmination of a brutal summer regime involving some 800km of high-intensity hitting, running, swimming, boxing and strength training.

Long revered as one of Australia’s most supreme athletes, Hewitt has worked ferociously on his game and fitness for almost six hours a day, six days a week – virtually non-stop – since early November in preparation for his Open swan song.

Attacking every session as if it were his last, the indefatigable former world No.1 has worn out a queue of hitting partners since commencing his exhausting eight-week block and left his decade-long conditioner in awe.

“In terms of endurance and durability playing professional sport at the highest level for 20 years, there wouldn’t be many athletes who could match it with Lleyton for intensity on a day-to-day basis,” fitness trainer Nathan Martin told AAP.

“He never gets sore. He turns up every day with the same energy and commitment. His body composition and genetics, he’s just blessed.”

Given his longevity over an 876-match career, an almost unrivalled five-set record and his attritional playing style where he’s scrapped and scrounged for nearly every point, Martin suspects few players in history would have covered more miles on court than the irrepressible two-time Grand Slam champion.

“For sheer volume of training and kilometres on court, only Connors could compare – but even still he wasn’t No.1 in the world at 20,” said Martin, who will launch the Lleyton Hewitt Tennis Pro Fitness app with the retiring champion next week.

A typical training day for Hewitt begins at 10am with a three-hour hitting session at his home in Sydney.

The baseline warrior will patrol one end, always taking on two at the other with tour battlers Matt Reid, Dayne Kelly, Matthew Barton and fellow Open hopefuls James Duckworth and Jordan Thompson his 2015 summer whipping boys.

“He’ll only stop about three times for two minutes max to have a drink,” Martin said.

A half-hour rest to take in “half a sandwich” and a protein shake will precede 90 minutes of conditioning work – anything from boxing, run-swim-runs, sprints, on-court agility, weights, stair climbs or shuttle, hill and sled runs.

Hewitt’s recovery session, focusing on rehydrating, nutrition and massage, can last up to an hour before he wraps up about 4pm.

He’ll then enjoy family time – often more physical activity in the form of basketball or tennis with his kids – and organise himself and his new Davis Cup charges before winding up with a 15-minute ice bath around 8 o’clock.

Hewitt’s fitness app, featuring 110 tennis-specific exercises and the 34-year-old’s favourite career moments, will offer opportunities for fans and budding pros to challenge themselves against the former Wimbledon and US Open champion.

Martin doubts anyone will come close to matching his exercise personal bests and is even more convinced that Hewitt – whose trainer estimates has clocked up a mind-boggling 15,000km and 7680 hours training for his record 20 Australian Open appearances – will be as physically prepared as ever for his Grand Slam farewell.

“Obviously how he goes will depend a lot on the draw,” Martin said.

“The only thing I know is that you’ll have to drag him off the court. He won’t lose. You’ll have to beat him.”

Hewitt, whose last three Grand Slam exits have come after five sapping sets, will launch his month-long 2016 campaign partnering Jarmila Gajdosova at the Hopman Cup in Perth starting on Sunday.