From this, a vicious cycle of spasm, congestion, and pain can evolve. Even though applying heat may feel good at the moment, it actually exacerbates the problem because the heat brings even more blood to the congested area and over stimulates the nerves supplying those muscles. When the heat is removed, the body cools off the area to return it to a normal temperature. The chilled muscles and the over stimulated nerves will often cause the muscles to continue to spasm.

If you apply ice for 20 minutes, it will numb the area and break the cycle of spasm. The cold sedates the nerves and causes the vessels to constrict, sending fluid and toxins away from the area. When the ice is removed, your body wants to bring the temperature back to normal and so flushes the area with fresh blood, bringing oxygen and nutrients to aid the healing process. The injured muscles are less likely to continue to spasm in this changed chemical environment.