Rotator cuff strengthening is vital due to the unique role played by the rotator cuff in shoulder stability. In my own mind I look on undertaking rotator cuff strength exercises as the final part of rotator cuff healing.
You may have had a rotator cuff tear or surgery, had some therapy, done the rehab and now it is time for strengthening. Undertaking exercises to strengthen rotator cuff muscles will actually help to stabilise the whole shoulder joint.
Training muscles to become stronger
As a general rule, a muscle will increase in strength when it is trained close to its current force generating capacity. What does that actually mean in practice? Well, put simply, it means that for any muscle to get stronger it must be worked close to the maximum it is already capable of. An example is that anyone who can already bench press 100lbs is not going to gain strength by bench pressing just 40lbs.
There are two main muscle actions when training and each can be used in rotator cuff strengthening. There is dynamic muscle action, when the muscle length changes, that can be split into concentric action and eccentric action. Then there is also Isometric action when the muscle does not change length but is working.
Dynamic - Concentric action
Dynamic concentric muscle action is when the muscle shortens and joint movement occurs as tension develops. An example is say you holding a weight in your hand, your arm is relaxed and hanging fully extended by your side. You slowly begin to lift the weight using your bicep muscle. This moves the arm from an extended to a flexed elbow position. The bicep muscle has performed a shortening or concentric action whilst moving the arm.
Dynamic - Eccentric muscle action
Dynamic - eccentric muscle action is, pretty much, the opposite of Concentric. It occurs when the external resistance exceeds force a muscle can exert and the muscle lengthens while developing tension. Using the same example as above the muscle works to slowly lower the weight against the force of gravity.
It has clearly established that a combination of concentric and eccentric muscle actions add to the success of any training. This in turn leads to superior muscle strength and increased muscle fibre size. The other notable benefit of combined eccentric and concentric training is that it is much better at consolidating gains.
Isometric muscle action
An isometric muscle action is when a muscle generates force, attempting to shorten, but cannot overcome some form of resistance. This type of action does not actually result in any real "work". Despite this an isometric or static action can generate substantial force. This is despite any noticeable lengthening or shortening of the muscle fibres or joint movement.
You just try pushing against a wall! No matter how much effort you put in that wall is unlikely to fall over. Your muscles will be working hard without any muscle lengthening or contraction. There will be no movement within any of the joints either. Despite this lack of movement you will be tired and have had a workout.