Whether for pre-operative knee osteoarthritis patients or after knee replacement, exercising quadriceps muscle strength and enhancing knee extension devices can have irreplaceable benefits for post-operative rehabilitation or protection of the knee joint. So how to exercise quadriceps muscle strength effectively? For those who have particularly weak quadriceps muscle strength and have difficulty raising the straight leg, you can start by flexing and extending the ankle joint in bed (see below) for 30 seconds each time, one set in the morning and one set in the evening, 20 to 30 times each. In addition, although you cannot lift your leg, you should also consciously practice straight leg raising to initially increase quadriceps muscle strength. For those who have weak quadriceps but can lift their legs straight off the bed, they can perform the muscle strength exercise of straight leg raise and dorsal extension of the ankle joint (see the figure below). Straight leg back extension ankle while lifting the leg, for 20 seconds (about the equivalent of a silent count of 20 in the mind), then lower the leg and plantar flexion ankle, also for 20 seconds, which is once; then repeat 20 to 30 times. Every day in the morning and evening each group. The key to the exercise of quadriceps muscle strength is to be persistent, and it is important to persist in order to receive results.