The coach has been running pressing and counter-attacking drills with his team in preseason and is hugely impressed with the effort being put in by the squad
The 46-year-old was referring to his side's desire to press and counterattack following the summer break, with preseason in full swing in Germany and the Bundesliga campaign around the corner.
With the DFL-Supercup coming up on Saturday July 27 against treble winners Bayern Munich, Klopp is delighted that his side is showing excellent effort in training.
"The boys do their [preseason training] like hyenas!" he told Bild. "The players have incredible fitness levels - the best we've ever had!"
On the back of a second-placed finish in 2012-13, Dortmund opens its new Bundesliga campaign on August 10 against Augsburg.