Training with resistance is a fantastic way to accelerate your metabolism. Resistance can come in the form of dumbbells, bands, body weight, or machines. All of these modalities raise your metabolic rate while you workout and also during recovery. Also, the muscle that you gain is metabolically active meaning that it burns calories even when you are at rest. Furthermore, you don't need to gain a ton of muscle to dramatically change your metabolism.
Studies have shown that any number of repetitions (within reason...let's say 30 or fewer) builds muscle. Sets of 8-12 repetitions generally build the most muscle while heavier weight with fewer repetitions develop more power. Performing a high number of repetitions typically produces greater gains in muscular endurance.
HOWEVER, our bodies are amazing adaptation machines! For that reason, after we have spent several weeks training in a particular repetition range our body adapts to that way of training. As that form of training becomes less stressful adaptation slows and sometimes even stalls. In the real world, we find exceptions to the rules set by the studies in large part because the studies are usually conducted over relatively short periods. If you've been working in the 8-12 rep range for many weeks chances are you'll build more muscle and see a greater boost to your metabolism by switching to a repetition range that would otherwise be considered best for power or muscular endurance. So to answer the initial question, the repetition range that will build the most muscle for you now is the one that will burn the most body fat.
About the author:
Brian Day is an Exercise Physiologist and NSCA Certified Personal Trainer and Strength and Conditioning Specialist based in Missouri City, Texas. He works with clients at his private personal training studio in Sienna, at client's homes in and around Missouri City, and everywhere online. Learn more at www.FitnessByDay.com or by calling or texting (617)794-6796.