coolcolj said:doesn't have to be done all out, 70-80% is best , cause 100% effort will wipe out your CNS if your also doing weights as well
can be done on any cardio type machine/movement - ie sprinting, rowing machine, treadmill etc
how can you tell 80% of your effort tho
heart rate?
or if you have an exercise bike I guess you could pedal your heart out at 100% for x time like 15 or 30 seconds whatever your hiit burst will be, and see the speed then keep to 80% of that?