The 18 year-old will join Spurs this summer.
He told Expressen: "There has been an awful lot of gym training. Lots of weights above all, back and front. Everything is possible.
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"I have become more physical in general, I get into more duels and cover the ball better.
"I have always run a lot and have put on many kilos and it feels like I have become even stronger this season.
"It's incredibly fun and a good proof that what you do is working."