Upper Leg

Upper leg injuries are relatively uncommon amongst runners. They are often caused by periods of sudden increased exercise such as sprinting. 

The two main areas are the Hamstring, which extends across two joints from the hip to the knee. A Hamstring Pull is likely a sudden pain, muscle spasm and loss of strength 

Hamstring

Hamstring Pull

The Quadriceps the large muscles at the front of the thigh can frequently be strained there will be a sudden pain, most probably when running downhill, and it is possible for the muscle to rupture completely. There is local tenderness and swelling, possibly from running downhill or a sprint start.

Quadriceps

Quadriceps Strain