Heat exhaustion and heat stroke unfortunately are not uncommon occurrences in athletic training and competition. Every year, several U.S. football players die as a result of heat stroke (6). Endurance events and military training also result in cases of exertional heat injuries (EHI) (5). Numerous organizations, including the American College of Sports Medicine (ACSM) and the National Athletic Trainers' Association (NATA) (1,3), have conducted extensive literature reviews and published recommendations to prevent the occurrence of EHI. They use the Wet-Bulb Globe Temperature Index (WBGTI) to guide athletic participation recommendations in the heat. If the WBGTI is too high, training and competitions are often canceled.
The U.S. military also uses a WBGTI, albeit more liberal, to guide its training and operations. Because of the increased demands of military personnel training and the baseline temperatures in current areas of operation, training and operations cannot be as readily canceled. As a result, additional preventive strategies have been used to allow continued operations in high WBGTI conditions. This includes the United States Marine Corps (USMC) training bases in South Carolina, Virginia, and North Carolina and operational forward bases in Okinawa, Japan. These places are very hot and humid in the summer, but training must continue, so EHI risk remains elevated. Marine Corps EHI-related morbidity and mortality has dramatically declined since the 1990s with employment of the current methodologies to prevent and treat heat casualties. Similar strategies can be applied to other team sporting activities. To provide analogies to team sports, consider the military commanding officer as the head coach, the section commanders as the assistant coaches, the unit commanders as the team captains, and the unit Marines as the players. The intent of this article is to review the preventive and treatment strategies currently used to allow U.S. Marines to train and operate in ACSM black flag conditions.
EHIs comprise a group of illnesses that usually, but not necessarily, occur while exerting in hot, humid environments. These include heat (parade) syncope, heat cramps, heat exhaustion, and exertional heat stroke (EHS). Heat syncope is characterized by fainting or collapse, likely is caused by peripheral pooling of blood, and recovery usually is rapid. Heat cramps or exercise-associated muscle cramps are painful, prolonged spasms of muscles after exercise and may be associated with electrolyte disturbances (sodium often is implicated), dehydration, and/or fatigue. Heat exhaustion is characterized by an inability to continue exercising in the heat without evidence supporting the diagnosis of EHS. Exertional heat stroke occurs when the patient presents with exertion-related hyperthermia (core body temperature > 40°C) and associated central nervous system disturbance or evidence of other end organ system damage. The EHS casualty's skin most often is sweaty and pale in humid environments in contrast to the dry skin of classic heat stroke (1).
Flag conditions based upon WBGTI have been recommended in the literature since at least 1986 in the ACSM Position Stand on Prevention of Thermal Injuries During Distance Running (2) and more recently in the current NATA Position Stand on Exertional Heat Illness (3,4). The USMC also uses a WGBTI-based flag condition system (8-10). The USMC system permits greater activity levels at higher WGBTI values than do the NATA and ACSM systems. Table 1 compares the temperature/flag designations for the ACSM/NATA and USMC; note that the USMC green flag conditions correspond to ACSM black flag conditions.
Training and activity guidelines have been written to coincide with these flag systems (Table 1). The guidelines start at a level generally considered safe for training and competition, which is green, and increase the level of risk until the flag is black. Once in black flag conditions, the ACSM and NATA guidelines recommend canceling a competitive event and canceling or significantly altering the practice depending on the athletes' level of conditioning and acclimatization. The USMC black flag guidelines also recommend stopping nonessential training, with the caveat that essential training can continue at a level commensurate with the Marines' conditioning and acclimatization level and include additional treatment readiness measures (dedicated medical personnel, ice water slurry with soaking towels and sheets, and communication with definitive treatment resources). "Essential training" is considered mission critical, that is, "activities associated with scheduled exercises or other major training evolutions where the disruption would cause undue burden on personnel or resources, be excessively expensive, or significantly reduce a unit's combat readiness" (9).
The Navy-Marine Corps Team has developed an effective process to prevent and treat EHI through the synergistic interaction of awareness training, EHI recognition, a buddy system, risk assessment, training modification, rest, refueling, and effective supervisory controls at all levels within the chain of command. The direction begins at the highest levels of the organization and, accordingly, EHI prevention is a leadership issue. The medical team augments the preexisting safety and risk management programs targeting all service members and designed to minimize mishaps both on and off duty that ultimately will affect operational readiness.
All service members are required to attend training annually, titled "The Critical Days of Summer Safety Campaign," addressing numerous topics to include EHI. Written orders and guidance governing EHI management are distributed widely and frequently reevaluated and updated. The annual EHI training presented to all Marines and supporting Navy personnel reviews the orders describing how to administer the EHI prevention and treatment process (8,9). These orders contain everything in the EHI continuum to include WGBTI determination, display of flag conditions, frequency of flag condition updates, and unique training requirements for all individuals. The senior nonmedical officers receive the same training, with special emphasis on risk management and leadership responsibilities. Primary care sports medicine physicians and the sports medicine staff provide additional EHI training to the medical staff at the hospitals, clinics, aid stations, and to the field corpsmen. The training provided to the physicians is aimed at understanding all aspects of EHI to include definitions, risk factors, clinical presentation, initial field treatment, definitive care, and return-to-duty criteria. "Train the trainer" sessions are then held with the corpsmen responsible for the individual Marine Corps units, providing them with an intense review of EHI prevention, EHI risk factors, risk factor recognition and elimination, signs and symptoms of EHI, and initial management algorithms (1,3,8,9). These corpsmen then provide every Marine in their small units with a review of EHI and develop a unit-specific prevention and management plan.
EHI RECOGNITION AND BUDDY SYSTEM
The ability to recognize pending EHI is vital to a successful prevention program. The empowerment of all individuals, up and down the chain of command, to identify EHI risk and bring it to the attention of responsible leaders requires a great deal of trust. A buddy system with a focus on the importance of truly knowing one another's baseline behavior and trusting that any EHI symptoms reported would be taken seriously and lead to early intervention and prevention is central to the process. Marines are taught to recognize evidence of EHI in each other, begin risk factor mitigation, and notify command leadership and medical support assets immediately. This awareness and early adjustment in training or operations minimizes the impact of EHI on the individual and on overall mission accomplishment.
RISK ASSESSMENT AND TRAINING MODIFICATIONS
Numerous factors and potential risks are considered and constantly reevaluated when developing and executing the training plan. Operational risk assessment is performed with every event. The week's weather forecast (estimated WGBTI) and previous day's heat exposure are considered during the development of training plans. The training plan is adjusted if exceptional heat and humidity are expected or experienced. Modifications in training may take the form of increased rest periods, decreased training duration and intensity, event substitution, and change of event location. Uniform and training gear is reduced to the minimum necessary to achieve the training goal. For example, certain training events require Marines to wear the full combat uniform, Individual Body Armor, Kevlar helmet, and fire-resistant gloves. Much of this uniform can be removed after the completion of the training exercise. Similarly, American football tackling drills should be performed in full protective equipment (helmet, shoulder pads, and padded pants), but once the drill has been completed, the pads and helmet can be removed. Acclimatization is accomplished by following one of several suggested schedules (8). These include a 6-wk schedule, a 21-d schedule, and an 8-d schedule specifically designed for rapid acclimatization for deployments (Table 2). Hydration and nutrition breaks are built into the training plan (the Marines have a saying: "Hydration is continuous and chow is continuous"); however, in combat there is no guaranteed lunch break. Tables 3 and 4 describe hydration and workload guides along with the recommendation for active cooling during breaks. Hydration primarily is accomplished with water, and electrolyte replenishment is accomplished by eating meals or snacks throughout the training evolution.
EFFECTIVE SUPERVISORY CONTROLS
The authority of Marine Corps leadership is not unlike that of many athletic organizations. The top of these leadership models has the ultimate responsibility for all functions under their command. Effective leadership in the area of EHI is demonstrated by using all of the previously discussed information and directing subordinates to supervise and control training with a prevention focus. The leader of the team must be alert to risks, personnel wellness, and deviations from a reasonable plan. They should readily adjust and adapt the training to the operational environment in order to prevent undue injury.
Despite the effectiveness of the Navy-Marine Corps preventive efforts, EHI may still occur. While recognizing that cold-water immersion is the gold standard for treating EHS, our training environments require an adaptation to this method. Because of the expansive and diverse geographic areas covered and the around-the-clock nature of operations, a standing tub of ice water is impractical. Instead, first responders within the units are equipped with sheets and towels soaked in ice water slurry and bags of ice. Initial treatment of suspected heat casualties is immediate placement in shade, removal of excessive clothing, and assessment of vital signs to include rectal temperature and mental status. If unable to obtain a rectal temperature, yet clinical suspicion remains high for the diagnosis of EHS or the casualty has a rectal temperature greater than 103°F and mental status changes consistent with EHS, immediate, aggressive cooling is initiated with ice water soaked sheets and towels wrapped around the person's body and head. The sheet and towel are removed and rotated back to the ice water slurry and replaced with a second cold set every minute. This aggressive cooling continues en route to a prepositioned cooling center. Upon arrival at the cooling center, the patient is placed on a mesh stretcher over a rigid pool of ambient temperature water. Staged bags of ice are opened, and the loose ice is placed on and around the groin, axilla, neck, and trunk to augment the cooling provided by ice water sheets and towels. Water from the pool is poured over the ice. This cooling is continued until the rectal temperature is less than 102°F. Cooling rates of up to 0.4°F ·min−1 have been observed (Flynn, S., unpublished data from Parris Island, 1998-1999) with this method, and in a recent study of this cooling method used at the Marine Corps Marathon, cooling rates of 0.24 +/− 0.05°F·min−1 were achieved with 100% survival (7). Final disposition of the patient is determined after a period of observation and further evaluation after the patient is cool. This modification of the gold-standard treatment emphasizes early, aggressive, pretransport cooling of EHS. Additionally, it may be an excellent way for an athletic team medical staff to immediately initiate treatment of EHS without always having a pool of ice water available.
The United States Marine Corps and United States Navy medical team have developed a successful EHI prevention program based upon awareness training, EHI recognition, a buddy system, risk assessment, training modification, rest, refueling and effective supervisory controls. These concepts mesh well with the established guidelines (1,3) and other EHI review articles. The Navy-Marine Corps EHI management plan could be applied to civilian athletics. Coaches and players should know the fundamentals of EHI. Coaches should know their players and trust their players' reports of symptoms. The medical team must be ready to educate, advise, recommend training modifications, and treat symptomatic athletes. As with the Marine Corps, the responsibility for the prevention of EHI lies with organizational leadership.