It's a Common Mistake
When dieting, some people use their lifting workout as their primary fat burning tool. They do so by dramatically increasing training volume and density – either by reducing rest periods or using supersets.
This was popularized by Charles Poliquin with his German Body Composition approach, and has been used by many experts to get rapid fat loss in clients.
I'm not saying that it doesn't work. By doing more volume, you'll need more energy to fuel the muscle contractions, which means a greater caloric expenditure. By using shorter rest intervals, you keep adrenaline higher, which also helps burn more calories, even after the workout is done.
I do use this kind of training with body composition clients, but NOT at the beginning of a fat loss plan.
If you start with this approach, you're painting yourself into a corner. Just like if you cut your calories too much too soon, or use fat burners right away. You're pretty much stuck having to keep up with that strategy for the duration of the plan, even making it more intense if you want to keep progressing.
And while the high volume, high-density approach works well, it comes with some drawbacks that make it less than ideal for longer periods of time... like a dramatic increase in cortisol levels.
When it comes to training, several variables can increase cortisol output:
- Volume: The more volume you do, the more energy you need to mobilize, and the more cortisol you release.
- Intensiveness: This is how hard you're pushing each set.
- Psychological Stress: If something creates a mental stress, like a super heavy weight or knowing in advance that you'll suffer, it increases cortisol more.
- Neurological Demands: The harder the brain needs to work, the more adrenaline you release to speed the brain up, the more you release cortisol to trigger that adrenaline increase.
- Density: The shorter the rest, the more cortisol you release to keep adrenaline high.
A high volume/high-density workout where you use big lifts and go to failure (or close to it) is among the highest cortisol-producing workouts you can do. That's fine for a short period of time.
But if you stick with it for too long you'll start to suffer the consequences like lowered testosterone/estrogen levels and a desensitization of the beta-adrenergic receptors. In that last case, it'll mean a dramatic drop in motivation and resilience, as well as physical and mental performance.
The Better Approach
When you begin your fat loss efforts, your training program should be lower in volume and focus more on heavy lifting.
You should also put training efficiency at a premium. For me, that means using a whole-body approach three days per week, using 3-4 big compound movements per session. Then I'll add a fourth workout using isolation exercises to hit the muscles that might've been neglected by the big lifts.
As you progress in the plan, gradually add volume. At the end of the leaning out phase, conclude with one, 3-4 week block where lifting is used as a fat loss tool.