And with double training sessions each day sharpening their fitness, Jackson says the players are in good shape with the season fast approaching.
The preparations intensify further this week with a friendly game at local rivals Preston on Wednesday followed by a visit to Macclesfield on Saturday.
Jackson told the Evening Post: "It was a great trip to Denmark and good for
the lads to spend five days together.
"The training facilities and pitch were excellent, right on the edge of the Baltic, and we got plenty of hard work done.
"We played two games which were fairly low-key but we used them as part of our training schedule.
"That's the best way at this time, although it was still pleasing to win them both 5-0 which shows we're heading in the right direction.
"The new lads were with us so the time away helped them integrate, and they all seemed to enjoy it.
"Perhaps the only downside of the trip was John Filan's gloating following after the first day of the Ashes series on Thursday!
"On a personal level, I played the whole of the first game and half the second, and the legs are feeling really good.
"We're back at work in Wigan today and are now looking forward to getting out on the pitch again at Preston on Wednesday night."
One of the new faces on the trip was former Liverpool and Blackburn centre-half Stephane Henchoz.
He spent a couple of days training with the squad in a bid to prove his fitness and earn himself a longer stay with Latics.
It's expected the former Switzerland international will train again with the club this week while negotiations over a contract take place.
Jackson said: "Stephane was only with us for a day-and-a-half but he played part of the first game and has a decent pedigree.
"I think he's coming back with us this week."
Jewell is keen to add a centre-half to the squad and Henchoz's experience in the top flight would be a bonus.
He has no doubts about the 30-year-old's ability but wanted to see him train to assess his fitness levels – he started only a handful of games for Liverpool, Celtic and Switzerland last season.
With Latics now back on home soil, transfer activity is expected to hot up.
They continue to be linked with Spurs midfielder Michael Brown and Wolves striker Carl Cort.
If Jewell was to land those targets, together with Henchoz, that would leave another central defender and a right winger on his wish list.
However, Jewell has dismissed reports that he is interested in Manchester City's troubled midfiedler Joey Barton.
Jewell said: "Barton is obviously a good player.
"I don't know what's gone on over there. He is a good player but not one I've thought of at the moment."