Wing Shane Williams has described Wales' preparations for the World Cup as the toughest of his career.
The Welsh squad's preparations for the tournament in New Zealand have included two 10-day training camps in Spala in Poland.
Warren Gatland's side face England at Twickenham on Saturday in the first of three World Cup warm-up matches.
"It has been one of the toughest couple of weeks I've had to face as a rugby player," said Williams.
"The first week in Poland for me was horrendous. It was really tough.
"Any training you were doing was always tested, always recorded so you could see where you are in comparison with other guys.
"The second week we acclimatised a lit bit more, [getting] a little bit fitter.
"But you can be as fit as you like really. It's all about doing it on the field as well. The boys are in a good place at the moment physically.
"They're looking strong in the gym. Mentally now is the big one and it all starts on Saturday against a very good English squad."
Williams will make his first appearance at any level since suffering a knee injury against Ireland in the Six Nations in March.
The Ospreys player has previously spoken of his intention to retire from international rugby after the World Cup in New Zealand.
He represented Wales at the previous two World Cups, although he very nearly missed out on a place in the 2003 squad.
It was Williams' display in a warm-up win over Romania, a game in which he scored two tries, which secured a World Cup place.
And the 34-year-old says players will doing everything to impress in Wales' three warm-up matches to earn a World Cup spot.
Following Saturday's trip to Twickenham, Wales will host England at the Millennium Stadium on Saturday 13 August before Argentina visit Cardiff on 20 August.
"A lot of guys at the moment, they'll be wanting to be involved in these games and where they are involved, play well," he said.
"The competition for places at the moment is fierce. You can't go into these games half-heartedly.
"One you're going to get injured and two, someone else may take your position and certainly people will be thinking about that.
"World Cup warm-ups [are] all about seeing where you are individually as players and as a team collectively. It's exciting times."
"There are two massive games coming up against England and physically [we're] going to see where we are as a side.
"We need to go out there now and perform to the best of our ability."
"[We've] got a strong squad here at the moment and everyone's putting their hands up in training to be selected.
"You've got to go one hundred percent in these games, give it your all and hopefully come out the other side smiling.
"It's going to be very difficult for us to get a result up there but we've just got to go out and basically throw everything at England.
"They're in the same position as us as well. They'll be wanting to prove a few points. It makes for a good game."
Coach Gatland is due to name his final 30-man squad on 22 August with Wales' opening World Cup game against South Africa on 11 September in Wellington.
Wales: Rhys Priestland (Scarlets); George North (Scarlets), Jonathan Davies (Scarlets), Jamie Roberts (Cardiff Blues), Shane Williams; Stephen Jones (Scarlets), Mike Phillips (Bayonne); Paul James (Ospreys), Huw Bennett (Ospreys), Craig Mitchell (Exeter), Bradley Davies (Blues), Alun Wyn Jones (Ospreys), Danny Lydiate (Newport Gwent Dragons), Toby Faletau (Dragons), Sam Warburton (Blues, capt).
Replacements: Lloyd Burns (Dragons), Ryan Bevington (Ospreys), Luke Charteris (Dragons), Ryan Jones (Ospreys), Tavis Knoyle (Scarlets), Scott Williams (Scarlets), Morgan Stoddart (Scarlets).