You Aren't Doing the Right Workout to Build Muscle

Workouts like barre [5], Pilates [6], as well as long runs all have their place and benefits, but if it's muscle you're after, weightlifting is your best bet. Instead of randomly selecting exercises with sets and reps schemes that don't make sense, you've got to design a proper workout plan.

Before you pick up a weight make sure your program focuses on muscle hypertrophy (maximal muscle growth), doing three to five sets of 12 to 15 reps per exercise, Rondel said. You'll also want to lift heavy (here's a guide to determining your weights [7]) and incorporate compound exercises [8] — multijoint movements that work large groups of muscle — into your workouts. On the days that you lift heavier, you should do eight or fewer reps, lifting a minimum of 80 percent of your one-rep max to help your muscles grow.

Don't forget to do your recovery work after training [9], and make sure you getting enough rest each night to help improve recovery and muscle growth.

You Aren't Doing Enough Strength Training Sessions Per Week to Build Muscle

If you're trying to build muscle, strength training one time a week won't benefit you. Instead, Rondel recommended doing a minimum of two to three days of strength training per week. You can design your program so that on one day you're lifting heavy, the next session you're doing more reps and a moderate weight, and then heavy again the following session.

Another option is to train in the hypertrophy phase for two weeks, followed by strength (heavier weights and fewer reps and sets) for two weeks, giving your body a different stimulus as your muscles grow and become stronger, Rondel said. Weight training alone won't be enough to help you build muscle. What you do in the kitchen is equally as important as what you do in the gym.

You Aren't Eating Enough to Build Muscle

"Gaining muscle is a very tough thing to do and you definitely have to factor in the quality of your nutrition, the timing of your nutrition because once again, when you're developing tissue, you always want to be in an anabolic state (when the body is building or repairing tissue) where you have the necessary energy in your body for your system to build tissue," Rondel told POPSUGAR. If you're trying to gain muscle but are constantly hungry, and you're going six and seven hours without eating, it will negatively impact your muscle gaining capacity, Rondel explained. "It will decrease it a whole lot," he said.

Bottom line, building muscle and following low-carb [10] or low-cal diets [11] won't work. "A lot comes down to what you're eating, and supplying your body with the necessary macronutrients [12] so you can then transfer it and turn it into muscle," he explained. Everyone's macronutrient profile (proteins, fats, and carbohydrates) will look different, so definitely consult a registered dietitian or nutrition coach to figure out what works best for you. In a previous interview, Jim White [13] told POPSUGAR your macronutrient profile for building muscle [14] should consist of 55 percent carbohydrates, 25 percent protein, and 20 percent fat.

If you're looking for a weightlifting program to follow, get started with this four-week plan to build muscle [15].