Doing Two Things at Once

One fundamental problem is that our bodies aren't typically good at doing two things at once, especially when those things are at odds with one another, or have different fundamental requirements. For example, study after study has shown that combining heavy strength training with heavy endurance training compromises the overall results. Why? Strength training sends the muscle a signal to become bigger and stronger and more efficient at using glucose for fuel; endurance training send a signal to become more energy efficient (which typically means smaller because smaller muscle fibers can get energy more readily) and utilize more fat for fuel. End result is that the body can't do both optimally and you get less than stellar results when you try to do both. How does this apply to losing fat and gaining muscle? In short, they have different (and, in fact, mutually exclusive) requirements. That is, gaining muscle and losing fat require different scenarios in terms of nutrition, hormones, etc. In fact, the specific requirements for gaining muscle are also the reason that you tend to gain fat at the same time. Similarly, the requirements for fat loss are part of the reason (along with your body's adaptations) that you will lose muscle at the same time. Thus, talk to a fitness expert and develop an exercise plan that delivers the results you seek.