If you're like most gym-goers, you send your body mixed messages. You walk into the gym thinking "grow!" but the life you lead, and the mistakes you make, too often say "whoa!"
When I say "mistakes," I'm not talking about using the wrong grip on lat pull-downs or pointing your toes out too far on calf raises. Honestly, muscle growth isn't as precise as that. No, it happens on a much bigger level, including a big growth stimulus provided by heavy lifts, large amounts of food, and an overall lifestyle commitment. If that last one made you squirm in your seat, then you definitely need to keep reading.
Here are six mistakes that could kill your gains. They're all easy to fix right now, so be honest and ask yourself: Which one is holding you back from your potential?

MISTAKE 1: NOT LISTENING TO YOUR BODY

YOU NEED TO LISTEN TO YOUR BODY AND WHAT IT'S ASKING—OR SCREAMING AT YOU.
You're scheduled to hit the gym for a big chest day today, but your triceps and front delts still ache from your last shoulder workout. You had mediocre sleep last night that left you feeling far less than energized. What do you do?
Many dedicated gym-goers will hit the gym anyway. They say there are some days you just have to push through. Which is true—to a point. There comes a time, though, when you're only stacking abuse on top of abuse.
You need to listen to your body and what it's asking—or screaming at you. Maybe it's saying that a day or two of straight-up, no-strings-attached rest is necessary.
Or perhaps it's telling you that knocking against the ceiling of your abilities every day isn't the way to go, and that a program with more built-in periodization is a better fit for your abilities and lifestyle.
Athletes learn and improve. You know who doesn't? Injured athletes. Muscle tears, strains, and systemic overtraining will all cost you time and muscle mass. Don't give up performance in the name of ego!

MISTAKE 2: MISSING OUT ON THE BIG LIFTS

Too often, we quantify our weaknesses purely in terms of size. "I'd like to add an inch to my arms," for instance, or "I wish my calves were bigger." So we approach the problem the same way we'd approach a bike with a flat tire: by pumping it up, in this case with isolation movements like preacher curls or calf raises.
Logical, right? But you build more overall muscle—and a surprising amount of site-specific muscle—by addressing big W: weakness. You should train to get stronger! 
Weighted pull-ups will do plenty for your arms, in addition to your back, abs, and overall strength. 
Heavy deadlifts hit your arms, calves, and pretty much everything else, while producing a rush of beneficial anabolic hormones and burning more calories than you probably realize.
Sure, curls and calf raises are great exercises, but if you want serious gains, you simply must hit heavy, basic compound movements. When I say heavy, I'm talking enough weight that you're fully fatigued after 8-10 reps. Keep your form strict and control the weight.
A good balance between compound exercises and isolation is crucial to the success in any mass-building program. Conversely, you could also plan out your year and focus solely on improving on the big movements for a phase, followed by a phase of more traditional bodybuilding work. How you choose to incorporate strength work is up to you. Just make it happen!

MISTAKE 3: NOT MASTERING MIND-MUSCLE CONTROL

Maybe because of all the intense faces that people make in the weight room, it can be easy to overlook how fun training is. It's like a playground for adults, with every station offering a different experience and potential for improvement.
With all these tools at our disposal, it can be tempting to simply move from station A to B, push weights from points A to B, and trust that it's working. If you've accomplished everything the little piece of paper said to do, the workout was a success, right?
IF YOU REALLY THINK ABOUT EACH MUSCLE FIBER SQUEEZING AND CONTRACTING AS YOU MOVE THE WEIGHT UPWARD, YOU'LL DIAL IN AND WORK THE MUSCLES YOU AIM TO.
Yes and no. In reality, half the battle is the process. If you really think about each muscle fiber squeezing and contracting as you move the weight upward, you'll dial in and work the muscles you aim to. You'll maximize the time under tension (TUT), which is a proven way to grow. Allowing stronger muscle groups to take over a movement pattern is the fastest way to miss out on gains in the muscle you target. Your front delts are all too willing to take over a shoddy bench press, for example.
Learn how to really focus in on a muscle, and you'll see an instant boost in how your workouts feel and your body grows. You also might find yourself making some of those intense faces I mentioned earlier—and that's a good thing!

MISTAKE 4: NOT STAYING ACCOUNTABLE DURING THE WEEKEND

For many serious trainees, staying accountable during the week isn't a problem. Their schedule is relatively constant, they can control when and what they eat, and they're able to avoid major dietary pitfalls.
Then the weekend hits, and all bets are off. Even if you just go out and "let loose" one evening each week, you can seriously set back your physique goals—especially if alcohol is involved.
A drink or two is one thing, but let's be honest: Getting straight-up drunk on a regular basis has no place in a serious athlete's life. Compromise is inevitable in fitness and in life, but it's still up to you to decide what's most important to you.
Are you willing to sacrifice maximum gains in order to have a few drinks? Or, is making the absolute most progress possible a top priority? If it is, then you'll want to stick to soda water with lemon or lime instead.

MISTAKE 5: OVERDOING CARDIO TO STAY LEAN

A lot of people these days like to say you don't need cardio at all, and that simply setting foot on a treadmill or trail is going to cost you gains and leave you skinny-fat. I'm not of those people. Cardio can have a place in most programs, but it's definitely possible to overdo it, particularly if you do hours of it every week in order to "stay lean" while trying to bulk. That's a big no-no if you're trying to add muscle.
First, overdoing cardio training can dramatically decrease your total force generation capacity, which may mean you don't have the energy to produce the growth stimulus you need during your lifting session. Remember, it's TUT that really pushes muscles to grow, and you need energy to produce it. And if you're eating to build muscle, you especially need to maximize your strength training. Otherwise, you set yourself up to add fat where muscle should be.
Second, too much cardio stacked on top of weight training can also cause your testosterone levels to drop. Men who have low testosterone levels tend to maintain higher body fat levels and lower levels of total lean mass. Those are two strikes against overdoing cardio.
OVERDOING CARDIO TRAINING CAN DRAMATICALLY DECREASE YOUR TOTAL FORCE GENERATION CAPACITY, WHICH MAY MEAN YOU DON'T HAVE THE ENERGY TO PRODUCE THE GROWTH STIMULUS YOU NEED DURING YOUR LIFTING SESSION.
Finally, low-intensity endurance work teaches your body to be more efficient. Cardio trains you to make a little bit of fuel last for lengthy periods of time. This is exactly opposite of what you want when trying to stay lean. You want to burn calories in a raging, inefficient inferno, while you keep throwing fuel on the fire in the form of food.
The answer: While trying to add muscle, stick to high-intensity interval training for cardio—provided that it doesn't interfere with your recovery. Save the low-intensity cardio for other training cycles throughout the year.

MISTAKE 6: UNDEREMPHASIZING CALORIES AND OVEREMPHASIZING PROTEIN

When someone tells their trainer that they're struggling to add muscle, the immediate reply is to consume more total calories—a great suggestion. But in the quest to both stay lean and add mass, trainees too often try to perform an elaborate macronutrient dance where they shoot protein intake through the roof while cutting carbs and sometimes fat. Bad idea, says Reid.
"Too many people go to the gym and train hard but don't eat enough calories to support gaining muscle mass and size. I have fallen victim of this in the past while trying to keep my body fat low and abs showing," he explains. "I would cut carbs down very low for long periods of time. All this did was kill all the gains I made over the previous few months."
SO WHEN AIMING TO BUILD MUSCLE, EAT MORE OF EVERYTHING, NOT JUST MORE PROTEIN.
There's no denying the importance of protein in any mass-building diet, and sure, you'll need more of this crucial macronutrient than someone who's sedentary. However, also remember that carbohydrates are what the body uses as fuel while it works to assemble protein into new muscle tissues.
If you don't have enough carbs, the protein you eat won't be put to good use. Likewise, fats are required for optimal hormonal levels, and your hormones are the foreman of your body's muscle construction crew.
So when aiming to build muscle, eat more of everything, not just more protein. Once you reach 1-1.25 grams of protein per pound, step back and make sure you do not neglect another macronutrient.