The real influencers on fat-loss and muscle synthesis comes from the coveted anabolic hormones Testosterone, Growth Hormone, and IGF-1. As testosterone increases, estrogen decreases. As growth hormone elevates, cortisol is suppressed. As Insulin-like Growth Factor 1 rises, catabolism is reduced. It's a beautiful thing - just ask the Russian Olympic Team.
These hormones are naturally occurring within your body, but the overall amount varies from person-to-person.
Your workout should be designed to increase anabolism, which contributes in the reduction of body fat and the preservation of lean muscle.
Workouts that follow High Intensity Interval Training methods, such as CrossFit, Boxing, and Treadmill Pushes, and Time Under Tension methods, such as Weight Training and Calisthenics, are extremely effective for the anabolic effect.