The calves and lower legs can be affected by various medical conditions. Some common ones include:

1. Calf strains: A strain is an injury to a muscle or tendon. Calf strains can cause pain and weakness in the lower legs.

2. Shin splints: Shin splints are a type of pain that occurs along the shin bone (tibia) due to overuse or overloading of the muscle and bone tissue.

3. Stress fractures: Stress fractures are small cracks in the bone that occur due to repetitive stress or overuse. They can occur in the lower legs, including the calves and shins.

4. Compartment syndrome: This is a condition in which the muscles and nerves in a specific compartment of the lower leg become swollen and press against the surrounding fascia (connective tissue). This can cause pain, numbness, and weakness in the lower leg.

5. Varicose veins: Varicose veins are swollen, twisted veins that are often visible under the skin. They can occur in the calves and lower legs and may cause aching, swelling, and a feeling of heaviness.

6. Deep vein thrombosis: This is a condition in which a blood clot forms in a deep vein, typically in the leg. Deep vein thrombosis can cause pain, swelling, and warmth in the affected leg.