NEIL Harris believes the "gruelling schedule" in Portugal will help the squad "refocus" as they prepare for the 2017-18 Championship campaign.
The Lions have been in their overseas training camp since last Thursday, where they are also playing two friendly games.
It's the third summer in a row Millwall have travelled to Portugal as part of their pre-season preparations.
The camp involves three sessions per day – including two on the training pitch and one gym session or video analysis and presentations.
Harris said: "It's a gruelling schedule for them, and for the staff because we are continuously reviewing, preparing. But it's in a lovely climate, a lovely location and it's a fantastic environment to work hard in.
"We've had a couple of weeks [at Calmont Road] but sometimes a change of scenery is key just to take them away for a bit of time to refocus. That week in Portugal over the last two years has really set us up for the season in terms of work and nailing down systems of play."
Harris also explained the difference between League One and the Championship is more mental than physical.
"Fitness levels won't necessary be higher, lads are fit at all levels," he said. "We saw that at Dartford, I thought their fitness levels were excellent.
"It's about athleticism now in terms of pace and power, and probably more than anything speed of thought. I keep reiterating it to the boys and hammering it home – they're probably sick of hearing it from me – but we have to be better, sharper in the mind and that's why we've brought in competitive players.
"The standard of training has certainly gone up from last year, without a shadow of a doubt."
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