Tabata
Twenty seconds on, ten off. Four minutes that feel like forty.
The protocol
Tabata is eight rounds of 20 seconds at all-out effort with 10 seconds of rest between them, four minutes total. It comes from a 1996 study on speed skaters, and the format stuck because it's brutally simple and brutally short.
Where it fits
True Tabata effort is close to maximal, which makes it a hard session in a tiny package or a finisher after strength work. Bike sprints, kettlebell swings, and bodyweight movements like burpees all work. Scaled-down versions at less than all-out effort are still a legitimate workout, just not the original protocol.
20s on, 10s off
Eight rounds at genuinely maximal effort.
4 minutes total
The whole protocol, warmup aside.
Best as a finisher
Short enough to bolt onto the end of another session.