1. You're Not Overtraining, You're Under-Recovering
Consider what weight training does to your body. By lifting weights, you are tearing down your muscles, so you don't gain muscle simply by lifting weights. You see gains only when you help your muscles recover from the work you do in the gym.
2. You're Focused On Testing Rather Than Building
Leave your ego at the gym door because it is holding you back from packing on muscle. A lot of people feel that they have to lift as much weight as they can. They want to test how strong they are today, rather than working on building their strength. They put more weight on the bar than they can handle and end up missing a lot of reps and failing their set. If you treat every workout like a competition, you are headed down a dead-end street. If you treat your workouts like building blocks that work together to achieve a greater goal, you will add muscle and get stronger.
3. You're Emphasizing Isolation And Machine Exercises Over Compound Lifts
There is definitely a time and place for isolation exercises. Everyone loves doing push-downs, bar curls, and lat pull-downs, and I'm no different. It's also true that a large portion of the gym population focuses heavily on isolation movements while neglecting the compound lifts. If your goal is to add muscle, think of your workout as a three-course meal. Your appetizer is the warm-up, your main course is the compound lifts, and dessert is the isolation exercises.
4. You Don't Have Enough Variety In Your Routine
Exercise variety is a key factor in building muscle. Remember when you first started working out and felt really sore the next day? Your muscles weren't used to performing the new exercises and were adapting to them. Whether you are an experienced trainer or a beginner, your muscles respond to new movements.