Backbends are generally considered invigorating and energizing. The exception to this would be passive backbends that involve laying over a block or bolster, which tend to have a more calming effect. Depending on the orientation of the pose, backbends can be effective for building strength in the spinal erectors (as in locust pose), the shoulders (as in wheel pose) or the quadriceps (as in camel pose). They can also be effective for increasing flexibility in the shoulders (camel pose), abs (wheel pose) or quads (via PNF in bow pose and/or camel pose). Many backbends are often safe for various shoulder, wrist, elbow, ankle and/or knee injuries. Gentle backbends can sometimes even be helpful in relieving lower back injuries. As always, you should use your discernment and move slowly to determine whether or not a given posture is going to be beneficial for a given injury.