Steady-state cardioContinuous training
Continuous exercise held at a constant, moderate intensity.
Steady state cardio is continuous exercise held at a roughly constant, submaximal intensity: a run, ride, row or brisk walk at an effort you could sustain for a long time rather than one broken into hard efforts and recoveries.
Its value is that it accumulates aerobic work cheaply. Large volumes of comfortable training build mitochondrial density, capillary networks and blood volume, and it costs little in recovery, which means it can be repeated often and stacked alongside strength training without competing for the same recovery budget.
It is the majority of what successful endurance athletes actually do. Descriptive studies of their training consistently show most time spent well below threshold, with a smaller portion at high intensity, which is the observation behind polarised training models.
Compared with intervals, it is less time efficient per session and far more repeatable. Intervals produce more adaptation per minute and cost far more to recover from, which is why two or three hard sessions a week alongside easy volume beats making everything hard.
For fat loss it holds no special advantage. The old fat burning zone idea, that lower intensities burn a higher proportion of fat and therefore more fat overall, confuses proportion with total; energy balance across the week decides the outcome.
The common failure is drift. Easy sessions creep up into a moderate middle that is too hard to recover from and too easy to drive adaptation, which is the rut most self coached runners end up in.
In practice, keep most of your aerobic time at an effort where you can hold a conversation, and use our heart rate zone calculator to make sure easy really is easy.