The German coach has been running pressing and counterattacking drills with his team in pre-season 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 counter-attack following the summer break, with pre-season 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 his side are showing excellent effort in training.
"The boys do their [pre-season 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 open their new Bundesliga campaign on August 10 against Augsburg.