Let me make one point before I continue. If distant running is one's sport, one's passion, than by all means, continue the journey. Longer, steady-state cardio will bring health benefits too. However, in the quest for low body fat, while preserving muscle mass, interval training is your ticket.
Shorter Interval Cardio
- fat and glucose provide the initial sources of fuel though glucose is a much larger contributor
- interval training never allows the body to adapt
- a body that cannot adapt is inefficient at fuel utilization, so it uses more of it, which is what we want, right
- higher caloric output in a short period
- the heart and lungs are forced to keep up with the continual fluctuations, thus improving cardiovascular function
- interval training creates a massive post-exercise metabolic disturbance, which equates to a significant energy expenditure during recovery (= fat on its way out)
Slower Steady-State Cardio
- fat and glucose provide the initial sources of fuel
- fat eventually become the primary source of fuel due to its aerobic nature (presence of oxygen)
- the body eventually adapts to steady-state cardio and becomes more efficient at fuel utilization, i.e., slows down the burning of fat as a fuel source
- lower caloric output
- heart and lung cardiovascular function remains mild in exertion
- the body returns to normal resting metabolism much sooner after completion
All you need to do is contrast a track athlete with an endurance athlete to know which protocol produces the better physique.
Make it a great day!