Lock George Kruis says Eddie Jones' rigorous training program has helped improve the fitness of England's squad for the Six Nations.
Jones has watched his side claim two wins out of two in the opening fortnight of the tournament, leaving them top of the table ahead of their first home match against Ireland.
Second-half dominance has been a characteristic of England's performances so far, particularly in Rome when they scored four unanswered tries as they beat Italy 40-9.
Kruis told the Rugby Football Union website: "Against Italy we ran a lot, there was quite a lot of ball in play so it was interesting and I felt like I had to puff hard but it was worth it.
"The way it [training] is structured there's no breaks in the session.
"They've got the ultimate resources, you can move from one thing to another easily and everything is very detailed and planned out so I think that's the difference, the intensity at training is higher."
England host Ireland at Twickenham on February 27.