Lewis Hamilton said that racing in Spain in mid-August was hard work, and very different from his previous visits to the Circuit de Barcelona-Catalunya.
Formula 1 completes thousands of laps here every year with pre-season testing and the Grand Prix itself which is normally held in mid-May.
This is the first time F1 has been at the venue at the height of summer, and Hamilton said it had made a huge difference to the challenge they face this weekend.
"It's summer, this is the first time I've definitely been here in Barcelona when it's this hot," he told Sky Sports F1's Johnny Herbert after the end of the session.
"Physically it's tough," he said after claiming his fifth Spanish GP pole on Saturday with a final pole position time of 1:15.584s. "It's so fast here. It's the fastest we've ever been round here. The foces on the body are intense.
"The problems are all physical. The amount you're able to brake now is even heavier than before so there's a lot of stress though your core. You're flat out through three and through nine so there's a lot of stress on your neck. Your whole body just wants to move to the side of the car.
"As it's so hot you have to be even more careful on the throttle not to overheat the rear tyres," he added. "The tyres are what we're really struggling with.
"You see us pulling around on the out lap, that's just to keep the temperature out of the tyres, but even with those slow laps you still have the temperatures rising. That's what we're trying to manage on those laps.
"Balance wise, I think it's quite windy if you look at the flags. You've got a head wind into turn 1, so it's pretty good going into turn 1 but then into turn 4 it's a tail wind, turn 9 you have a tail wind, turn 10 you have a tail wind.
"There's corners where you know you can push and some where you can't, and you're still trying to find that limit. And that's when the car snaps away.
"But it's what we all do, and I have a huge amount of respect for all the guys here who are battling the same if not similar issues as myself."
Hamilton's pole time was set on his first run of Q3. His team mate Valtteri bottas improved on his second run but was just short of pipping Hamilton to pole, despite the Briton failing to improve.
"I couldn't go quicker on my second lap," he said. "I thought I could, but it just wasn't a great lap. But the first one was decent I guess, which did the job thankfully.
"These guys do such a tremendous job. We're constantly learning. I was here with the guys until ten o'clock last night looking at all the areas we could improve.
Bottas admitted that it was frustrating to miss out on pole to his team mate by just 0.059s.
"I knew it was going to be close with Lewis the whole way," he admitted afterwards. "In the end the first run he did was nice and clean, especially sector three.
"All day today I've been struggling a bit in sector three, he pointed out. "It was getting better and better but still not quite good enough.
"Of course it's annoying, but we did a good job. And as a team again [we got] front row!"
The result of qualifying sets up another tense head-to-hear duel between the Mercedes pair at the start of tomorrow' race, with Bottas keenly aware that he will have to apply pressure on Hamilton into the first corner.
"I think the start will be the best opportunity for me," he said. "On Friday my long runs were competitive, so I will have the pace but whoever gets [into turn 1] first will have the best chance.
"I will try to get there first. Trust me!"
Hamilton is keenly aware of the dangers he faces as polesitter for tomorrow's race, not only from his team mate alongside him but also Red Bull's Max Verstappen and Racing Point's Sergio Perez on row 2.
"It's such a long way here down to turn 1," he said. "The job is not done, that's for sure. It's very hard to follow here.
"Positioning is good, but it will be hard to hold position but that's what I've got to work on and try and get the best start I can."
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