The contribution of cardiovascular exercise and NEAT (non-exercise activity thermogenesis) to TEE (Total Energy Expenditure) hits the point of diminishing returns quite swiftly.
Refer to study below:
https://www.ncbi.nlm.nih.gov/pubmed/26832439
"Here we tested a Constrained total energy expenditure model, in which total energy expenditure increases with physical activity at low activity levels but plateaus at higher activity levels as the body adapts to maintain total energy expenditure within a narrow range. We compared total energy expenditure, measured using doubly labeled water, against physical activity, measured using accelerometry, for a large (n = 332) sample of adults living in five populations. After adjusting for body size and composition, total energy expenditure was positively correlated with physical activity, but the relationship was markedly stronger over the lower range of physical activity. For subjects in the upper range of physical activity, total energy expenditure plateaued, supporting a Constrained total energy expenditure model.
Models of energy balance employed in public health should be revised to better reflect the constrained nature of total energy expenditure and the complex effects of physical activity on metabolic physiology.”
What might explain why this happens? Could be due to reduction in non-muscular physiological activities: reproductive activities, somatic maintenance, inflammation, etc.
An argument can be made that past a certain intensity threshold (e.g. Michael Phelps, Lance Armstrong, etc.), constrained total energy expenditure may not apply. However, most people are either not willing or unable to perform at this intensity level for extended periods of time. You should also take into account how this could impact recovery and muscle retention.
With regards to TEE, comparing cardiovascular exercise to total calorie intake is like comparing apples to oranges. They are not interchangeable.
Does constrained total energy expenditure apply to decreasing calorie intake (as opposed to increasing cardiovascular exercise)? In my experience, no.
The takeaway is that—with regards to fat loss—manipulating nutrition is going to be much more effective than increasing cardiovascular exercise.
I generally start clients on a resistance training regimen of 4-5 days/week with cardiovascular exercise set at no more than 30 minutes per day (moderate intensity).