Standard CPR is performed with the person in supine position. Prone CPR or reverse CPR is CPR performed on a person lying on their chest, by turning the head to the side and compressing the back.
Non-spinal structural causes of weak legs may include sacroiliac joint pain syndromes and piriformis syndrome. Non-sciatica related sources of weakness in the legs may include diabetes, peripheral neuropathy and various circulatory and neurological conditions.
Weakness in the legs usually means one is tired or ill, according to Healthgrades. Sudden weakness in the leg can signal a much more serious condition, such as sciatica, which occurs due to pinching of the nerves in the spinal cord.