At the gym, I have been using the tank more.
https://www.torquefitness.com/collec...SAAEgJmd_D_BwE
I can push it for 35 seconds along the length of the gym and then back. One of the racers in my track training group uses the tank as well. He goes for 3 minutes non stop. It is hard to push the tank and there are some explosive moves that can be done as well as just pushing. Very hard on the legs.