By Dr Paul Batman, PhD.
The deltoid is a large hooded multipennate muscle on the lateral aspect of the shoulder giving it a rounded appearance. It consists of three parts, an anterior, middle and a posterior.
Lateral one third clavicle, acromion process and the spine of the scapula.
The deltoid belongs to the following muscle groups:
Shoulder joint flexors, shoulder joint extensors, shoulder joint abductors, shoulder joint horizontal abductors, shoulder joint horizontal adductors, shoulder joint diagonal abductors, shoulder joint medial rotators and lateral rotators.
Front arm raises (flexors), one arm dumbbell row (extensors), shoulder press (abductors), bench press (horizontal adductors), bent over row (horizontal abductors), cable rotates (medial and lateral rotators), dumbbell lateral raise, upright row (abductors)
CASE STUDY STRENGTH EXERCISE: UPRIGHT ROW
1. Stand in upright position with your back flat
2. Hold a barbell with a pronated grip and hands a “two thumb” distance apart
3. Slightly bend your knees with the barbell resting on your thighs
4. Contract your abdominals to protect your lower back
5. Begin the exercise by bending your elbows and lifting them as high as possible to the side of the body
6. Keep the bar close to the chest on the way up
7. At the end of the movement the bar should be directly beneath your lower jaw
8. Pause and then lower the barbell down slowly to the starting position
9. Your elbows should be almost fully extended at the end of the movement
Lovers combo, double arm chest stretch, leaning shoulder stretch (extension), shoulder abductor stretch.
CASE STUDY STRETCHING EXERCISE: SHOULDER ABDUCTOR STRETCH
1. Stand in an upright position with your arms by the side of your body
2. Gently move your straight right arm across and behind your body
3. Grip your right wrist with your left hand and gently continue to pull your straight right arm behind your body until you feel a comfortable stretch on the side of your shoulder
4. Hold the stretch for approximately 20 seconds and then return your right arm back to the starting position
5. Repeat the stretch on your left arm
Place your hand over your lateral shoulder just below the tip. Abduct your shoulder against resistance.
- Although the deltoid comprises three areas, they are all active to some degree in all shoulder joint movements.
- The anterior fibres are more active in shoulder joint flexion, shoulder joint horizontal adduction and medial rotation. The middle fibres are more active in shoulder joint abduction and horizontal abduction. The posterior fibres are more active in shoulder joint horizontal abduction, shoulder joint extension and lateral rotation.
- The middle portion of the deltoid is a powerful abductor of the humerus. Its greatest activity is between 90-110 degrees of abduction. The deltoid is the primary muscle that allows the arm to be raised above the chest for extended periods of time.
- The contraction of the deltoid assists in shoulder joint stabilization by pulling the humeral head up into the glenoid cavity. Its multipennate form gives it a strong stabilizing force.
- The position of the shoulder joint prior to abduction can have a dramatic effect on the fibre recruitment and shoulder girdle involvement
Abduction – Medial Rotation (upright row) involves more posterior deltoid and requires the shoulder girdle to move earlier.
Abduction – Neutral (Anatomical Position) (dumbbell lateral raise) involves more middle deltoid.
Abduction – Lateral Rotation (shoulder press)involves the anterior and middle fibres. This movement disengages the greater tubercle behind the acromion and causes shoulder girdle movements to occur later. This requires greater stabilization of the scapula.