Hi - thanks for that!
Physiologically, the more effort you put into exercise, the more fat you will use. Steady state is advocated because compliance is better compared with a harder programme (as you allude to above).
Too many people get caught up on the fact that you burn a higher % of fat at lower heart rate levels - however 50% of 100Cal is still 50Cal but 20% of 1000Cal is 200Cal!!
Simply put, the harder you work and the longer you can do it, the better the results will be. The hard thing is identifying exactly what the client wants and then what lengths they will go to achieve it.
I recently started training with a client who is a woman. I needed a spotter for my weights and she could do with the advice. I am pushing her harder than she has ever gone before in her weights and she is feeling the benefits. I do it safely of course but so many of our patients simply say they don't know how hard to go so they go easily because it is safer.
I have to spend a lot of time re-educating my clients who have been brain-washed by myths floating around out there...
Thanks!