Isometric exercises involve the static conditioning of muscles, meaning the muscle is not lengthened. Doing isometrics at submaximal effort means not performing the isometric exercises at full effort.
Submaximal vs. Maximal
One example of a submaximal exercise is to hold a weight in your hand and do a lateral raise, bringing the weight just to shoulder level, and stopping and holding. In a maximal exercise, more effort is exerted such as when pushing against a heavy object.
This mild strengthening exercise is ideal for injury rehabilitation because of how gentle it is on the joints and because it does not lengthen the muscle. You can choose a comfortable weight and lift it to achieve strength benefits without causing further harm to your shoulder.
Submaximal Exercises to Aid in Shoulder Recovery
There are several standard strengthening exercises that can be performed at submaximal effort, according to Your Orthopaedic Connection. You can do a shoulder external rotation by lying on your side, holding a light weight with your elbow bent at a 90-degree angle and lifting it up and away from your stomach to the point where it feels comfortable, yet challenging.
Warm Up and Cool Down
It is always good to warm up with a good walk and light stretching before performing any exercises. Even though you are working at submaximal effort, you still need to prepare your muscles and stretch once you have finished.