Tìm vị trí điểm đau. Mát xa bằng cách chà ngón tay dọc theo điểm đau. Sử dụng quả bóng quần vợt. Sử dụng con lăn xốp. Kéo dài tầm với.

Given the above summary, write a detailed text in English for it.
Most knots occur in your upper back and shoulder area. They tend to feel tighter and denser than the surrounding muscles, much like a knot in a rope (hence the name). Although knots can feel tight and denser, there are times that the most painful knots don't feel tight at all. Focus more on the fact that pressing into a knot produces pain, rather than looking for a "tight" muscle. If you press on a knot, it may cause pain to radiate outward. This suggests that it is a trigger point. “Tender spots” do not usually cause pain in other areas of your body. Gently rub the knot in a circular motion using your fingertips. Apply light pressure, but not so much that it hurts. This may help release tense muscle fibers.  You may also find that simply pressing on the knot helps relieve the pain. Apply firm pressure to the knot and hold it for about a minute.  If it is difficult or impossible for you to massage the knot yourself, ask a friend to help you. You can do this either leaning against the wall or lying down. Either way, put the tennis ball between you and the hard surface. Line it up on top of the point where you feel the most pressure. You may feel discomfort at first, but it should subside as you continue to apply pressure.  Pin the tennis ball between the knot and the hard surface until the pain ceases. Take breaks as necessary. At the beginning, you may find that you can only hold it there for a few seconds. As you continue this exercise, that time will increase. You can use other types of balls, but firmer balls such as racquetballs may apply too much pressure, at least at first. Foam rollers operate on the same principle as the tennis ball across a wider area. They can help release tense and tight muscles. They’re usually a couple of feet long and look like thick pool noodles.  Go slowly at first. Spending too much time on a sore spot can actually cause increased damage to your muscles, especially if you’re unfamiliar with foam rolling techniques. Spend 15–30 seconds on a knot before moving on.  Place the...