Bad form on shoulder day is a fairly common occurrence. If you're lucky, you'll find yourself the object of a gym-fail video on YouTube. If you're unlucky, you'll find yourself with a rotator-cuff injury.

We all make mistakes, but we can and should learn from them, I've identified nine of the most common blunders I see people commit on shoulder day, and provided ways for you to correct them.

The overhead press may be your go-to multijoint movement for shoulders, but that doesn't mean all its variations work your deltoid musculature the same. Not even close! That's why you should understand how each variation works a bit differently so you can pick the right tool for the job.

For example, lowering a barbell in front of or behind your head actually changes the emphasis on your deltoids, as does your elbow position relative to your torso. When you press overhead with dumbbells, your upper arms go straight out to your sides; that's your cue that your middle delt is positioned to undergo maximal contraction.

When you do Arnold presses or barbell presses in which the bar is in front of your head, notice how your elbows pull forward—they're no longer directly out to your sides. That slight shift recruits the front delts and relieves some of the tension from the middle delts. While that doesn't discount the effectiveness of these kinds of presses as great shoulder movements, they're not the best at emphasizing the middle delts.

Dumbbell and barbell presses in which you take the bar behind your head will better target the middle delt region. Machine overhead presses differ by manufacturer, but if you keep an eye on the direction of your upper arm, you can easily pick out whether you're getting much contribution from the front delt.

If you want more tension on your front delts when doing overhead presses, by all means choose the front barbell version, or consider Arnold presses.

All kinds of things can go wrong with too much weight on the bar, especially when you press that weight over your head. In the all-too-common scenario where you bend backwards to press more weight, your body searches for a way to gain better leverage. This can quickly turn an overhead press into a steep incline press, which recruits the chest musculature to a greater degree puts your lower back at risk.

Note that this overexaggeration of the spine comes with a steep price, and I'm not just talking about the reduced stimulus for your delts. To press safely, you want your spine in a neutral or slightly arched position with your core muscles—both on the front (abs) and back (low back)—braced and contracted. But that's not what's going on here. The hyperextended position of the thoracic and lumbar vertebrae combined with heavy weight can contribute to a herniated disc.

When doing seated overhead shoulder presses, keep your back pressed fully against the bench. When doing them standing, be aware of overaggressive arching. You'll certainly want a degree of arch in your back, but don't turn the exercise into a dangerous standing incline.

While some lifters slip into a 3-sets-of-10 mentality for the bulk of their training career, many others cycle heavy and lighter training periods. While doing low-rep training with heavy weights can help build stronger delts, it might be a mistake when you're loading extra plates on the bar and repping it behind your head.

When doing a behind-the-neck barbell presses, the shoulder muscles are in their weakest anatomical position at the bottom of the move. Using too much weight on this movement can increase the risk of a tear, according to Guillermo Escalante, DSc, CSCS.

Escalante recommends going in front of the head if you're going to use very heavy weight, although doing the behind-neck overhead presses with moderate weight is a safe way to target the meat of your delts.

To work your middle delts maximally, you want your upper arms moving directly out to your sides. That happens by taking a moderate grip on a bar when doing upright rows, not an extremely close grip.

If you take a close grip on the bar, watch where your elbows go. They move forward and out to your sides, not directly out. Using a close grip causes internal shoulder rotation, which isn't always healthy for your joints. This not only put less emphasis on the middle delts, but also increases the likelihood that you could have long-term shoulder damage.

Push your grip wider on the bar to allow your elbows to kick directly out to your sides, which is perfect for building up your middle delts.

Many trainers terminate single-joint movements like lateral raises and front raises when they hit roughly shoulder height, but the middle and anterior delts haven't reached the ends of their range of motion. In fact, you can take these movements even higher, as the muscles are still contracting. Some experts suggest you can go as far as 45 degrees past the horizontal plane.

The longer range of motion makes these movements harder, so you may sacrifice a bit of weight, but the extra range and time under tension makes these moves worth adding to your workout every so often in conjunction with heavier single-joint exercises taken to about shoulder height.

I'd like to say this is a mistake only beginners make, but it's commonly done wrong among intermediate lifters, as well. I've preached over and over again about the importance of keeping your arms locked in a slightly bent position when doing single-joint exercises like lateral raises, front raises, and bent-over lateral raises, regardless of the type of equipment you're using.

Once you start closing and opening up at the elbows, the triceps become part of the equation, reducing the effectiveness of the isolation you're trying to achieve with single-joint delt exercises. On movements like lateral raises and reverse standing cable flyes, many lifters mistakenly completely extend their elbows to 180 degrees at the end of the movement, then close them to about 90 degrees as they lower the weights. Using a weight that's too heavy is oftentimes the culprit.

If you're extending your elbows on shoulder exercises, congratulations: You now have a terrific triceps move. Too bad it's shoulder day!

While we're focusing on elbow extension here, it's worth noting that you don't want to fully lock out your elbow joints as you complete the move from start to finish, which puts pressure on the joint itself. Lock a very slight bend in your elbows that you hold throughout the range of motion.

Your delts comprise three heads: the front, middle, and posterior. Some guys actually train them in that order because that's what they see looking back at them in the mirror, and that's usually a big mistake.

Guys who focus on building a big chest may have well-developed anterior deltoids (which contribute in all chest-pressing motions), but they could be lacking strong overall development.

If you've neglected back training, your rear delts are probably small in comparison to your front and middle delts, which sets you up for possible rotator-cuff complications down the road. It may also cause your shoulders to pull noticeably forward, giving you a slouched appearance.

If you've got a lagging area—which for most lifters is the rear delts—more often than not, do single-joint moves for that area first (after your presses) when your energy levels are highest, or consider doing a second single-joint movement for that area.

If your delts are fairly evenly developed, you can rotate the order in which you train them from one workout to the next, to ensure balanced development. If you always do one area last in your workout, however, it will begin to lag behind the others over time.

Training is exhausting, let alone spending extra time on muscles you can't see and stretches that don't pack on size. That's why rotator-cuff training is at the bottom of everyone's list. But the rotators—a group of four strap muscles that work in coordination with the delts—help stabilize the shoulder joint.

When you train your delts—and chest, for that matter—but skip your rotators, the ratio of the strength between the two muscle groups can become imbalanced, and that increases your risk of a rotator-cuff injury. Any longtime lifter will tell you the importance of healthy rotator cuffs.

The shoulders, especially the anterior delts, are commonly recruited in chest movements, and your triceps assist in overhead pressing motions, so how you arrange your training split is important.

If you train chest and/or triceps the same day as delts, you're fine. If not, it's wise to insert at least two days before or after your chest day to ensure you don't overuse your delts. For example, don't train chest on Mondays, shoulders on Tuesdays, and triceps on Wednesdays. Insert pull-day workouts (back or biceps), legs, or rest days to allow ample recovery time for muscle recovery.

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