Solskjaer is putting his squad through a tough fitness program.
"It's about pre-season and that's what it is," said Solskjaer. “They should feel tired, they should feel that they're gaining something from it.
“We're building fitness, robustness, mental robustness and it's been very encouraging. They have been great.
“Of course, we have also worked on a couple of new tactical approaches and ways that we think can benefit us this year."
Meanwhile, Diogo Dalot believes the intensity of the sessions will benefit the Reds during the upcoming Premier League campaign.
“Yeah, of course [it has been hard work]," he said.
“That is why pre-season is hard, because this is the time when we need to push hard and work hard, because it is going to be the first step of the season. Double sessions [or] only one session, we need to go hard in every session."