Interim Chelsea manager Guus Hiddink said the players "needed a bit more rugby" in their training programme after going soft under former boss Jose Mourinho.
Hiddink has steered Chelsea in the right direction since replacing Mourinho in December, suffering one defeat in 14 matches in all competitions.
The Dutchman arrived at Stamford Bridge with Chelsea languishing in 16th position, just one point above the relegation zone, but the Londoners are now 11th and through to the FA Cup quarter-finals.
Hiddink's appointment has provided renewed aggression in the squad, evident by a training-ground bust-up between Oscar and Diego Costa.
And Hiddink - a former PE teacher - believes Chelsea are benefiting from a wide range of sports on the training ground.
"I make a combination of handball and rugby, for warming up [his players]. Because in rugby - I love to see rugby also - you are entitled, when one has the ball, to grab and make a wrestling move," Hiddink said ahead of Tuesday's Premier League fixture against Norwich City.
"I was brought up as a physical teacher in the academies. I loved to do all the sports and people were brought up to practise those sports. When I was 18, 19, you get your physical education and I did boxing as well [as judo].
"It's a nice sport and if you train for boxing it's one of the toughest for endurance and aggression. Physically it's very tough but I liked it very much."
Hiddink added: "If they are going into a fight - within the rules - in football, then I think you can gain a lot from other sports, including rugby.
"We installed and organised in my time at PSV a kind of wrestling with the youngsters, because on the pitch you have this physical contact and if you do those exercises you get a very good feeling of balance, how you can fight in your duels and so on. That's very important.
"I'm strongly in favour of wrestling [to develop footballers], especially in terms of how you fall. You're not afraid to fall and if you jump, you manage to land like a cat. If you have that experience as a youngster it will benefit you a lot."