Described is a new method of treating chronic compartment syndrome in a muscle of a mammal, particularly exertional compartment syndrome. The method includes introducing an effective amount of a nerve-blocking toxin, such as human botulinum toxin into the muscle. Further in addition to treating chronic or exertional compartment syndrome, a method is included and described in the disclosure of confirming diagnosis of exertional compartment syndrome in a muscle of a mammal. In the method, venous compression and/or expansion in a mammal in an area of a muscle having a symptom associated with exertional compartment syndrome is evaluated by comparing venous flow at rest and after stress on the muscle. An anaesthetic is used to block a nerve supplying motor function to the muscle causing compression of a blood vessel. The mammal is evaluated after the block of the nerve to determine if the symptom associated with exertional compartment syndrome is alleviated.