Sprints, rows, or jump squats — go all out, then rest.
A well-known McMaster trial found that three weekly sessions of just one minute of hard sprinting (split into three 20-second efforts) produced cardiometabolic improvements, including markers tied to heart and metabolic health, comparable to 50 minutes of continuous moderate cardio. More recent work using RNA sequencing and proteomics has shown sprint-style efforts switch on stress-response and mitochondrial quality-control pathways in muscle cells in a way continuous cardio doesn't, reshaping how those cells function at a molecular level.