Southampton players admit their first day of preseason under new manager Ronald Koeman was tough.
"It was difficult," Ward-Prowse told the club's website.
"Obviously VO2 max means you run to your maximum and you can't run anymore, so it's difficult. It stands us in good stead to go and tackle the rest of pre-season and the season beyond.
"In midfield you've got to be able to do a bit of both. You've got to get in the box to score goals and get back to defend. It's a very physical, demanding position but that's why I enjoy it."
Jack Cork added: "It was hard. We do it nearly every season and I thought with the new gaffer coming in we might dodge it this year and get away with not having to do it!
"It's one thing that keeps me motivated in pre-season to try and do some work because I know the first thing I'm going to do is have something like that to test me straight away. It's hard but it helps us with all the data."
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