Weakness is decreased strength in one or more muscles. Weakness may be total body or local to a specific body part or muscle. You may feel weak with having mono or the flu. Weakness may also be due to metabolic reasons (low sodium/potassium, hypothyroidism), neurologic (stroke, bells palsy, cerebral palsy, multiple sclerosis), toxic (botulism, shellfish poisoning), and primary musculature diseases (muscular dystrophy). After a thorough evaluation, physical therapy may include instruction in exercises to help strengthen weak areas, education in posture to decrease stress to joints and muscles and manual therapy if needed for alignment and alleviate tight muscles.