Intense training methods such as cross training and boot camp training also increase the risk of severe muscle injury that can be debilitating or even life threatening. Overzealous cross trainers may develop rhabdomyolysis (rhabdo). Which involves destruction of muscle tissue that results from the release of the muscle cell contents into the bloodstream. Toxic chemicals include myoglobin, creatine kinase, potassium, lactate dehydrogenase, uric acid, calcium, aspartate transaminase, alanine transaminase and phosphorus. The incidence of rhabdo has increased alarmingly with the popularity of high-intensity training programs. Approximately 3 percent of people involved in physical training programs for the military, police and firefighter experience rhabdo. Physicians across the country have reported an increased incidence in ordinary people performing extreme physical training programs in health clubs. The exact percentage is unknown, but experts believe that the incidence is underreported.