Larry Benson is treating compartment syndrome of the lower leg.
A muscle in the compartment of your leg can become engorged with blood during exercise. This squeezes the nerve and can choke off the flow of blood coming to and leaving the compartment.
Symptoms include tightness of the lower leg, pain, swelling and weakness it gets worse after exercise.
Treatment includes ice, relative rest and compartment testing are helpful. At its worst, surgery may be necessary.