A veteran of almost 25-years of motorcycle grand prix competition in places like Malaysia, Thailand, Indonesia and Qatar, Valentino Rossi put last Sunday's COTA MotoGP race as among the most physically difficult of his career.

As well as 32-dgree air temperature and 46% Texan humidity, riders faced 20-laps around the longest (5.5km) circuit on the calendar, containing hard braking, fast changes of direction and energy-sapping bumps.

"It was one of the most difficult races of my career from the physical side because this track is very demanding and it was so hot, with a lot of hard braking, a lot of changes of direction and a lot of bumps. It was really, really difficult," said Rossi.

Things didn't start well for the Petronas Yamaha rider, who had qualified just 20th on the grid, but then dropped to last on the opening lap.

However, some consistent pace combined with mistakes by several riders ahead, plus passes on countrymen Danilo Petrucci and Franco Morbidelli, at least saw Rossi reach 15th and a world championship point by lap 11, where he remained to the flag.

"At the end I did a decent race considering my pace because I put the medium rear and I was not particularly fast but I was constant to the end. I was able to do some overtaking and take one point," he said. "So at the end it's okay. The problem is that I was not fast enough, I was not competitive enough. I hoped to be stronger, but the pace was not fantastic. But anyway the race, for my speed, was quite good."

While lacking outright speed, Rossi had been one of only three riders not to use the softest rear tyre (in his case a medium) and set his best lap of the race (only 20th fastest) on the last lap.

"I used the medium because during practice I felt better with the medium and I don’t like a lot the soft," Rossi said. "[In warm-up] I tried the soft but I was too slow.

"So we decided to continue in our way and it was the right choice because it was constant until the end, I was able to do some overtakes and take one point. It's nothing fantastic but considering my speed the race was not too bad."

The nine-time world champion now has just three races left before the end of his record-breaking career, starting with a final home appearance at Misano later this month.

"The physical conditions [at COTA] were very very difficult. Very tough. Now we will rest for 2-3 days and after we have to train hard for the last races," Rossi said.

"With the modern MotoGP it's very demanding physically and you arrive on Sunday already tired from the Friday and Saturday practice, so it's very difficult.

"You have to be 100% fit and also very young. I can try for 100% fit but for very young, unfortunately for me, that's very difficult!" joked the 42-year-old.

Rossi is just 21st in the world championship standings and one point behind brother Luca Marini, who will headline the VR46 MotoGP team next season.