Fernando Alonso admits readjusting to the speeds of Formula 1 is "not so easy" after driving the 2020 Renault on Tuesday.

The double world champion stepped up preparations ahead of his big return with his first outing in F1 machinery since April last year at the Circuit de Barcelona-Catalunya.

And though running was limited by the regulations, Alonso will more than excited by his first taste of action with the team that will be known as Alpine from next season.

"It has been a very good day in Barcelona, our filming day,” he commented afterwards.

"Only 100kms, but for me they were very special, getting back to an F1 car and to the team.

"The feeling was good. I think the car is obviously outperforming me at the moment because I cannot extract the maximum from the car.

“Getting back to the F1 speed is not so easy. I was improving lap after lap and trying to give feedback to the engineers.

"Also we had some filming to do, so there were cameras, there were drones following on track. So it was hard pressure, hard work today.

"I think the car has potential, as we see every weekend, but still some room to improve, as we know, and we'll try to do it in the shorter term.”

On settling back in as a full-time F1 driver, Alonso did concede it would likely require less time than the other categories he has tried since leaving the grid at the end of 2018. 

“With the F1 it's a little bit easier because it's the thing that I've been driving all my life," he said.

"After 18 years in F1 and now getting back, it's true you are missing a little bit the braking points, how quick all the corners arrive, braking performance, cornering speed performance, there are many things that I need to get used to again.

"But it will take a shorter period of time than getting used to a completely new thing, for example, Dakar and Indy."

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Another important element of preparation will be the physical aspect of readjusting back to the fastest racing cars in the world, which many feel could be the hardest part for the now 39-year-old.

"There are many things to get ready," Alonso continued.

"First will be the fitness – you have to be back in shape, you have to train for F1 standards, the neck, especially all this part of the body, the upper part, will need to be reinforced and worked on in the next couple of months.

"The neck is OK after 100kms, but I will tell you tomorrow! Maybe a little bit of pain. So far it has been good, but I know that I need to keep working.

"Then preparations in terms of comfort, seat fitting, the steering wheel, pedal positions, there are many things we need to go through," he added.

"Also the engineers, trying to have a good relationship, a good connection, that we understand each other even just looking at each other.

"All those kinds of things, we will need a bit of time. We are using this part of 2020 and also the winter of next year to build the momentum."

Alonso's return to the track came just two days after Renault returned to the podium for the first time in a decade at the Eifel Grand Prix, this after Daniel Ricciardo finished third at the Nurburgring.

That results came as the Enstone-based outfit has been making strong gains in recent races, putting them back in the fight for third in the Constructors' Championship.

And when it comes to adding Alonso back into the mix, team boss Cyril Abiteboul admits that is a level which must be sustained.

“We know from Fernando that he doesn’t make any mistakes,” he told Auto Motor und Sport. “We have no excuses. We have to improve on the execution on the track.”