It can be disappointing when you're working hard to lift weights and train your body, but you're just not seeing the results that you want. Your muscles may still look puny compared to the others in the gym or perhaps your arms have extra flab that you figured should be gone by now. If this is you, you may be making one of these mistakes:

Mistake #1: Resting Too Much

We all need to rest between sets, but resting too long can lower your heart rate and stop your body from refueling your muscles. It's recommended that you rest for 30 to 90 seconds between sets. However, that can be too long if you're training more than one muscle group at a time. Focus on one muscle at a time, and give it no more than a 30 second rest between each set to see better gains.

Mistake #2: Using Only Free Weights

While I'm a proponent of using free weights, the truth is that often it's better to use cable and cam machines as well as free weights. For example, one of the best exercises for your lats is the wide-grip pull down, which demands a machine. Stick with the free weights for compound exercises, and be willing to mix it up with the various machines and free weights in order to get the best muscle activation for each exercise.

Mistake #3: Consistency

Consistency is a good thing in training, but never changing anything with your workout can lead to stagnation and fitness plateaus. If you want to really kick things into high gear, switch things up often. Your body gets accustomed to a workout after four to six weeks, so change your rep range to keep your muscles guessing.

Mistake #4: Not Enough Sets

Depending on the rep range you're working, each muscle and muscle group requires a different number of sets.

Your quads, chest and back need the most, while your abs, forearms, and calves need the fewest. Your triceps demand more attention than your biceps, and your lower back should be worked harder than your sides.

Your goal should be eight to 10 sets per muscle per workout, and two or three days between workouts. This will give your muscles the push they need, but still enable you to recover.

Mistake #5: Too Much Cardio

While cardio is great for burning fat, it's not as effective for muscle-building. Not only does it use up the glucose your muscles need for energy, but it can actually degrade the metabolism of the muscle tissue as well. A bit of cardio is important, but if muscle building is your ultimate goal, you should limit the amount of cardio you do.

Stick with three or four steady-state, low-intensity workouts per week, or two or three high-intensity workouts.

Mistake #6: Not Eating Enough

This is a mistake made by many lifters, despite the fact that they're eating more than normal. The purpose of increasing food intake is to increase the amount of energy available during your workout, but that doesn't mean you should eat more all day long--or whatever you want.

You should be eating more protein and healthy fats, and keeping your carbs at a normal level. Carbs aren't going to give you long-term energy for your muscle-building, so only increase your intake of protein and fats.