The shoulder complex is (as the phrase suggests) a complex set of joints where the clavicles (collar-bones), humerus (upper arm bone), and scapula (shoulder blades) intersect. This area is prone to injury if you go too heavy too soon, so focus more on strict form and lighter weights, and hit all the angles to ensure fully rounded development.
See above for a great workout video by IFBB bodybuilder and online personal trainer Jake Alvarez. He starts with the shoulder press, and explains the safest way to get the dumbbells into position. When you perform this movement, do a warm-up set with light weights first. The rest of the workout focuses on the rear (posterior) delts, often neglected by gym-goers. Jake demonstrates the rear delt flyes in a seated position (which gives him more control than the standing position). Then he moves on to the face-pulls at the cable-crossover machine using the rope attachment, but performs it lying on his back (face-up) to isolate the rear delts and prevent other muscles assisting the movement. Note how he squeezes at maximum contraction for a couple of seconds each rep. Finally he performs the reverse pec dec rear delt exercise. Not every gym has this machine, most of the gyms in London don't have it, but some high-end bodybuilding gyms like Equinox Gym in Kensington High Street have this machine.
The all-time master of bodybuilding Arnold Schwarzenegger was a firm believer that the shoulder muscles respond best to heavy weights. Be wary of this advice though, as the shoulders are a complex joint and prone to injury if you don't establish a solid base of strength and flexibility before you start with heavy shoulder training. Arnie was aiming this tip at established bodybuilders who wanted to reach the next level.
"Right from the beginning I recommend you do movements like the clean and press...this will build up shoulder mass and strength." (Arnold Schwarzenegger)
Don't get into the bad habit of just doing one favourite shoulder exercise. Your shoulders will look their best once you achieve good muscular development from all angles.
The shoulder muscles - the deltoids - are made up of 3 portions: anterior (front delts), lateral (side or mid delts), and posterior (rear delts). Make sure you develop all 3 portions for a fully balanced pair of shoulder muscles. Make sure you exercise your delts with correct technique, to avoid shoulder injury. Don't go too heavy too soon! And make sure you stretch your shoulder muscles thoroughly after your workout, to avoid tight shoulders.
This is what Arnold Schwarzenegger's Encyclopedia of Bodybuilding says on the subject of well-balanced shoulder development:
"Width - the development of the side head of the deltoid - is only one aspect of the total development of the deltoid muscles. Shoulders also need to be thick, to show development in the front and the rear."
All three portions of the deltoids insert into the upper arm (to be precise, at the deltoid tuberosity half way down the lateral surface of the humerus, the bone of the upper arm). All your shoulder joint muscles move the humerus (the bone of the upper arm) in a range of directions, whether its forwards/backwards/out to the side.
Where are the points of origin of the delts? The anterior portion originates at the lateral third of the clavicle (collar bone). The mid portion originates at the knobbly bone at the top of your arm known as the acromion process of the scapula (shoulder blade). And the rear portion originates at the upper rear portion of the scapula. The shoulder girdle refers to muscles that move the scapular.
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Make sure you warm up your shoulder muscles with light weights before training with heavier weights. The shoulders are a complex part of the body and are easily injured (particularly the rotator cuff muscles, see below), so it's well worth taking extra care to warm up thoroughly. Never use heavy weights for your shoulder workout, without having built up to that weight gradually and incrementally over time.
Anterior Delts (front delts)
Here are the best exercises for the front delts are:
Dumbbell alternate front raise
Barbell front raise - make sure your legs are slightly bent at the knees, to cushion the lower back and prevent injury.
The side delts are best stimulated with these exercises:
Dumbbell lateral side raise (light weights performed slowly are very effective. Too heavy weights are counterproductive, as the trapezius muscles take over)
Seated dumbbell press above head (known as 'military press', make sure you don't squirm around or arch your back to squeeze out the last rep, or you'll injure yourself. Also keep your neck and face relaxed throughout the movement. And avoid the temptation to wriggle around as you try to squeeze out that last rep. This endangers your spine. Keep your mid-section firm and still as your perform this exercise. And don't arch your back, keep it pushed against the vertical back of the bench. Make sure you have good core strength (including spinal erector muscles) before attempting heavy weights, or you'll risk spinal compression injuries.
Smith machine press (don't rely exculsively on machines for shoulder exercises, use dumbbells primarily, and machines occasionally)
Standing barbell row - this also activates your trapezius (the diamond shaped muscle that runs from the neck then spans out to your shoulders, then tapers down to your lower-mid back)
Lateral raise with cables machine
All lateral raises are initiated by one of the rotator cuff muscles, the supraspinatus, which is easily damaged if you attempt this movement with excessive weights.
The best exercises are:
Bent-over dumbbell lateral raise (make sure you use light weights and perform slowly) - Bend over and stick your bum out. Keep your weight on your heels. Don't shrug but rather aim to squeeze your shoulder blades together at the top of the movment.
Reverse Flye - lie face down on a bench, and lift a pair of light dumbbells out to the side, with your arms almost straight but very slightly bent at the elbows. You can vary the angle of the bench up to 45 degrees and all the angles in between, for a more rounded development of the rear delts.
Your rotator cuff muscles are a set of 4 smaller muscles which stabilise the head of your upper arm bone (the humerus) in the glenoid cavity of your shoulder blade (scapular). The tendons of these 4 muscles form a circle around this joint. They not only prevent dislocation of this joint under load, but also ensure sufficient distance between the bones to avoid impingement. In other words, these muscles ensure flexibility and stability throughout your shoulder joint's full range of movement.
The rotator cuff muscles are: supraspinatis, subscapularis, infraspinatus, and teres minor. Without a regular regime of exercising and stretching, these muscles are vulnerable to injury. Most people make the mistake of neglecting these muscles altogether. If you sit at your computer for much of the day, you've probably got internally rotated shoulders, as a result of tight rotator cuff muscles.
Best exercises: internal and external rotation with a light dumbbell.
There is no end to the variety of combinations you can use to stimulate the shoulder muscles. A few sessions with a personal trainer will give you some fresh ideas to give your shoulder workout a turbo boost, and help you squeeze out the crucial last few reps to failure in each set. If you can't afford a personal trainer, find a gym buddy whose goals are similar to yours, so you can train together and motivate each other.
If you have narrow shoulders, and want to develop broad shoulders, you need to address your posture, particularly the position of your scapular (shoulder blades) which affects the position of your shoulders. You can improve the posture of your scapula over time by a combination of exercises and stretching, and this is best achieved with the guidance of a personal trainer or physiotherapist.
One muscle (among several) which affects your scapula position is the serratus anterior, a much neglected muscle, which if developed properly will address the problem of scapula-winging, where the shoulder blades stick out and cause the shoulders to hunch forward and appear narrow.
You can immediately improve your posture by retracting your shoulders back, and puffing your chest out, and sitting up straight rather than slouching. If you work at a desk all day, it's important to get up and stretch every 15 minutes, and make sure you don't slouch at your desk. Likewise when you're relaxing on the couch in front of the TV, get up every 15 minutes and stretch.