Low intensity steady state cardio or LISS can be defined as cardiovascular exercise such as jogging, walking, etc done for 30-60 minutes at a rate of 60% of the maximal heart rate. High intensity interval training or HIIT (not to be confused with HIT bodybuilding training) is doing an exercise (burpees or sprints) at a very intense level (85-95% of your maximum heart rate) for 30s to a few minutes then resting and repeating. Usually its kept to a max of 30 minutes but can be as short as 5 minutes. For example, you could do a max set of burpees for 1 minute rest for 30s then repeat for 5-6 rounds. Or sprint 200m walk for 60s sprint 200m until a mile (1600m) is reached.
According to one study where one group did HIIT cardio and another endurance training. The HIIT group lost over 3x as much fat despite only expending half the calories.
Combining both strategies (ie some days of HIIT and other days of LISS) may increase the amount of fat loss than doing either alone.
Larger losses of bodyweight can affect VO2Max by up to a 40% amount.
VO2max is the maximum amount of oxygen your body can take in, deliver and use in one minute. It’s commonly used to access cardiovascular fitness. You can test your VO2max at home doing the beep test, or 12 minute run (Cooper test).
A study researched the effect of doing 4 rounds of 4 minute HIIT intervals, 10 rounds of 1 minute HIIT intervals and 45 minutes of steady state cardio on VO2 max. The group doing 4 rounds of 4 minute intervals increased VO2 max by 10%, the other HIIT group by 3.3% and the other group by 3.1%.
If you want to run ultramarathons or are a long distance runner HIIT may be less necessary for you to train. If you are new to exercise you should adapt to cardiovascular training for 6 weeks prior to engaging in it. If you are primarily focused on bodybuilding if you find cardio dull you could do HIIT instead to maintain cardiovascular health and for fat loss. However, I think some individuals who require a high level of physical fitness in their career or sport should mix up short intense cardio with longer slower cardio. And I cannot see why someone shouldn’t try to reap the benefits of both. However the studies lean towards HIIT more than LISS in my opinion in terms of VO2 max training and fat loss.
With HIIT you can also do it without a track or treadmill at home. And since it doesn’t take a long time people have no excuse not to ignore cardio especially since it seems superior for boosting VO2max and fat loss.