In modern police training, the primary targets are large nerve clusters, such as the common peroneal nerve in the mid-thigh and large, easily targetable muscle groups, such as the quadriceps and biceps. The baton is swung in fast, "snapping" strikes to these areas, sometimes only making contact with the tip. Taken together, these are intended to impair the subject's ability to continue advancing (by striking the leg) or attack (by striking the arm) by causing transitory neurapraxia (temporary muscle pain, spasm and paralysis due to nerve injury). Modern systems strictly prohibit hitting the skull, sternum, spine, or groin unless such an attack is conducted in defense of life, with many jurisdictions considering this deadly force.