Rowing or AB/bike erg workout
Intervals, alt time with partner
1st - 3 min on / 3min off
2nd - 2 min on / 2min off
3rd - 1 min on / 1 min off
try increase speed each round. I would do 80-85 % on first, 85-90% on second and 90% on last 1 min interval.
Your result is total calories.