Whether you run for exercise or for sport, there are few other natural body motions that can compete with the overall caloric burn of running in general. Occasionally, running can lead to muscle problems severe enough to require surgery and months of rehabilitation. If you've recently been running and heard a loud pop in your calf muscle, this may be a sign your running days have been temporarily put on hold.
A popping sound in the calf muscle can be a sign of a sprained calf muscle. Muscle sprains are three grades: a grade one sprain will result in no more than slight stiffness and a mild ache, and should heal on its own inside of a week; a grade two sprain results in mild swelling, pain when you walk and may require immobilization for several weeks; a grade three sprain means you tore 90 percent or more of the muscle. You will likely have a considerable amount of bruising and swelling, intense pain and little to no control over the muscle itself.
If you are experiencing no symptoms after the popping sound, it's possible the pop itself came from your knee or ankle joints. Much like when you "pop your knuckles," joints can make popping sounds when they are used extensively. The reason for this is the presence of synovial fluid in your joints, which is essentially a lubricant to keep your joints moving friction free. This fluid contains multiple gases like oxygen and nitrogen. Occasionally, when a joint moves in a particular direction, these gases escape and make a popping noise.
Whether you're symptom free, or you can barely walk, it's important that you seek medical attention following your run. A small muscle strain or pull can be just a simple injury that heals on its own in just a few days; however, without rest and proper treatment, even relatively minor injuries can lead to much more severe injuries. If a muscle has been strained and you continue to run on it, the weakened muscle fibers may begin tearing due to overuse. You may also compensate for an injured calf on one side by using your other side more, thus increasing your chance of injuring other smaller muscles that aren't use to so much stress.
To reduce swelling, the American Academy of Orthopaedic Surgeons recommends icing the R.I.C.E. treatment --- rest, ice, compression and elevation. Stay off your calf muscle until you can have it properly diagnosed by a medical professional. Ice the muscle for 15 to 20 minutes every two hours for the first 48 hours. Wrap your calf with an elastic bandage for additional support. Keep your calf elevated, as too much blood rushing to the calf immediately post-injury can lead to extensive tissue damage.