Virgil van Dijk says he had to "step up" his game when he joined Liverpool for £75m in January.
The former Celtic and Southampton centre-back, 26, scored on his debut at Anfield against Everton in the FA Cup.
However, Van Dijk says he has needed time to adapt to Jurgen Klopp's high-tempo, pressing style of play.
"I am getting used to how we play," he told Football Focus. "The intensity of our game is a lot higher than what I was used to."
The Netherlands international added: "Every day here is tough. We work very hard, run a lot and there is a big difference. I needed to step up my game, especially in the beginning. "
Van Dijk joined the Saints from Celtic for £13m in September 2015.
He had been expected to move to Liverpool last summer after he handed in a transfer request but a move fell through when the Anfield club apologised for making an alleged illegal approach and he was forced to train alone by manager Mauricio Pellegrino.
|Southampton 2016-17||Liverpool 2017-18|
|Distance per 90 mins (km)||8.3||9.2|
|Sprints per 90 mins||30.2||34|
A late Van Dijk header settled a Merseyside derby in the FA Cup third round on 5 January.
Speaking about his debut he added: "It was a crazy and busy week, something special that I will never forget. I wasn't even supposed to start the [Everton] game."
Liverpool are third in the Premier League, two points behind Manchester United, and thrashed Porto 5-0 in the first leg of their Champions League last-16 tie.
"I came here to achieve everything possible," said Van Dijk.
"I made the choice to come here base on everything. I love the fans, the atmosphere in the stadium and at away games. The quality we have in our team is unbelievable. I am proud and happy to be here.
"Klopp is very good and an amazing guy as well. A lot of the attributes he has makes us achieve good things in the future."
You can watch the full interview on Football Focus on BBC One on Saturday from 12:00 GMT.