Move your arms out so that they are out of the path of the knee for the same reason.
If the knee is still at the 90-degree angle, then you’re likely creating injury at this point. Shoulder Stabilizing Your shoulders can come to full extension without your arms. If your shoulder is still at the 90-degree angle, you’ll have some internal rotation and then the problem is often shoulder pain, especially into the upper back. What to do about it If your shoulder is in neutral, you should feel the top of your shoulder blade through the palm of your hand. Breathe through your nose to feel the stretch throughout your muscles, especially in your back. Lie on your back, and try to extend your right shoulder until it releases in your hands. If it doesn’t, then you’re not getting enough air into your back. Breathing through your nose increases the pressure of your diaphragm against your spine and chest.
Slowly lower your shoulder until it releases at the point on your body where your shoulder blade should be. Repeat this process on the other side. Shoulder mobility To help improve mobility for your shoulder, perform this mobility exercise. For this exercise, you’ll need to lie on your back with your arms out to the side. Raise your chin onto your chest until your shoulder blades are parallel to each other, and then lift your arms as high as possible. Make sure to maintain a tension in your hands and arms so that your hands don’t come together, and don’t let your shoulders drop down.
Repeat on both sides for a total of three sets of 30 repetitions each. Once you feel comfortable with the movement, add in some gluteal movement for added challenge. Shoulder Pressing In this exercise, you’re going to be holding your dumbbells in a flat-squat position, and at the top position of that movement, you’ll want to press the dumbbells directly overhead with your shoulder toward the sky. The weight should feel a little heavy at this point. Breathe into your hands and arms while focusing on the weight in your hands. To make it more challenging, slowly inhale and exhale with the weight in your hands. On the next rep, you’re going to go with a slightly bigger weight.