Short on/off intervals such as 30 seconds hard and 30 seconds easy are an alternative to long reps. They let you run faster than VO2max pace while the easy part keeps oxygen uptake elevated.
Common formats: 30/30, 40/20 or 15/15, usually in sets of 8-12 reps, sometimes repeated in two or three sets
The “on” part is often around 3K pace or slightly faster; the “off” part is a float or easy jog, not standing still
Because each rep is short, many people find them mentally easier and the running mechanics stay better
Research suggests both short and long formats can improve VO2max; neither is clearly superior for everyone
A simple progression: start with 2 sets of 8×30/30 with 3 minutes easy between sets. Over a few weeks move to 2×10, then 3×8. Keep the pace of the fast part constant; adding reps is the progression, not pushing the pace.