If you don’t recognize heat-related illnesses before they sneak up on you, they could ruin your hunt
One of the common myths about heat-related dangers is that they are a concern only in extremely hot weather. Not true. Heat-caused illness, including fatal heat stroke, can occur in ambient air temperatures as low as 70 degrees Fahrenheit. Another mistaken notion is that heat exhaustion and stroke afflict mainly the elderly and the infirm and those in poor physical condition. Also not true. Heat exhaustion and exertional heatstroke (EHS) can overwhelm anyone, including Olympic athletes in peak condition.
Heat stress can cause an array of disorders, including temporary (but often excruciating) muscle cramps; mild to severe dehydration; fatigue and/or general weakness; mental confusion and physical clumsiness; anxiety; hyperventilation; fast heartbeat; fainting; heat exhaustion, and, most dangerous of all, heatstroke, a life-threatening condition.
All of these problems can be thought of as existing on a continuum of heat-stress effects on the human body, from the comparatively minor to the severe and deadly. If you understand how heat strain works and then take the appropriate steps to minimize or prevent it, you can avoid serious illness. As a side benefit, you’ll also be able to hunt more comfortably and effectively, even in fairly extreme conditions that have less heat-savvy companions wilting.
Like most mammals, humans have a fairly narrow range of acceptable internal temperature. When our core temperature rises even a degree or two above that norm, the body responds by initiating defenses against the threat of hyperthermia, or overheating.
First adrenaline is released to stimulate blood flow and dilation of the near-surface or “shell” blood vessels. Adrenaline also triggers sweating. More than three million glands (most densely concentrated on the chest, back, face, scalp, palms of the hands and soles of the feet) release sweat on the surface of the skin. Myriad vessels carry core-heated blood near the skin’s surface, helping to vaporize the sweat.
Evaporating sweat absorbs heat from the skin and carries it away, into the air. Veins then direct the cooled blood back to the core organs, and the heat-dissipation cycle continues until core temperature returns to normal. A neat system. As physiologists say, the skin is “the main organ of thermoregulation in humans” (yes, the skin is an organ; the body’s largest), and evaporative cooling of sweat is our main defense against overheating in a stressfully hot environment.
What makes an environment “stressfully hot?” Many people think of heat mainly in terms of a high ambient air temperature, but the reality is more complex, involving a combination of influencing factors. Ambient temperature is the most obvious. Mother, as most of us realize, is relative humidity. Sweat is only cooling when it vaporizes into the surrounding air, but the damper the air, the slower the rate of evaporation. The well-known “heat index” adjusts for temperature combined with humidity. For instance, a 90-degree F ambient temperature combined with 90 percent relative humidity creates a stifling “apparent” or felt the temperature of 122 degrees. Yet even this adjusted figure can be less than frilly accurate.
An important but often neglected heat factor is the level and intensity of solar radiation, or “solar load.” The solar load can be a significant source of heat gain, especially in tropical, subtropical, desert, and high-altitude environments. Depending on intensity; direct sun rays can add as much as 15 degrees F to the heat index calculation. Think of a bright, 80-degree day with 70 percent humidity–a heat-index of 85 degrees, which doesn’t sound too bad. Now add 10 degrees of solar load. That brings the actual heat burden up to 95 degrees, clearly in the potential-for-danger range.
Another significant external influence on apparent heat is the amount of air movement around the skin. The more wind or breeze, the faster the rate of sweat evaporation and the greater the cooling effect. Conversely, the calmer the air, the harder it is to cool off, and the risk of overheating increases. In very humid, still air, sweat might merely pool and drip from the skin, burning up the body’s water supply but providing no relief from the heat.
(Tip: periodically towel off collected or dripping sweat to clear the skin’s surface for better evaporative cooling.)
Water loss through copious sweating–dehydration–is one of the major causes of heat illness. Studies have shown that people exerting themselves in a hot environment “never voluntarily drink as much water as they lose even when initially thirsty, and they usually replace only two-thirds of the net water loss.” Physicians call this tendency “voluntary dehydration,” and warn that its negative effects are cumulative, often building over a period of days, paving the way for a sudden-seeming, disabling heat illness. To prevent this danger, simply stay conscious of your body’s need for lots of water.
“Pre-hydrate” by drinking a pint or more of water before you begin any kind of exertion in the heat; then maintain hydration by drinking regularly throughout the day, even when you don’t feel thirsty. Maintenance amounts vary according to how much you’re exerting and sweating but generally require somewhere between a pint and a quart of water per hour of strenuous physical effort with heavy perspiring. In extreme heat stress situations, however, it’s possible to need as much as two liters (approximately a half-gallon) per hour. The general rule is to err on the safe side of more water rather than less.
Also, remember that alcohol and caffeine are dehydrating; if you consume either during nonhunting hours, compensate by increasing your water intake accordingly. To check your hydration level, monitor the color of your urine, which should be clear to light yellow. Darkening urine is a sign of dehydration and a signal that you need to drink more water throughout the day.
Staying hydrated will not only help prevent heat illness, it will help you function with maximum mental alertness, physical aptitude, and safety. Even a moderate level of dehydration/overheating can affect your judgment, decision-making, coordination, reaction time, attention to detail, and short-term memory. Other early dehydration symptoms can (but don’t always) include general weakness or fatigue; muscle cramps (especially in the legs and/or abdomen); nausea; a headache; confusion, and fainting (“heat syncope”).
If you experience any of these symptoms, cease all exertion, get to a shaded or cool area, rest and rehydrate by steadily sipping an appropriate liquid. (Gulping it down too fast can induce vomiting.) So-called sports drinks, which contain vitamins and electrolytes such as potassium and sodium, are fine (especially if you are having muscle cramps, which indicates a salt depletion from heavy sweating), but they will not rehydrate you any faster than plain water. Cold liquid, however, empties faster from the stomach than warm liquid and is more palatable as well.
Along with dehydration, and often connected with it, there is another major cause of heat illness: overexertion. When sitting at rest, the body’s metabolic processes generate a certain amount of heat. But walking, climbing, running, lifting, and so on, can increase the inner-generated heat by as much as 20 times the resting level. This can strain or simply overwhelm the body’s ability to cool itself adequately.
Highly motivated individuals, such as athletes, soldiers, and eager hunters, are especially prone to exerting themselves unsafely. Peer pressure (hunting companions) and wanting to please authority (the guide or PH, for instance) are often involved in voluntary overexertion in the heat. This is dangerous behavior because, as noted earlier, even young athletes can suffer potentially fatal exertional heatstroke if they push themselves too hard.
There are two good ways to minimize the risk of overexertion. The first is to acclimate or condition yourself to heat stress, preferably before you venture off to a very warm or hot clime. To do this, you simply need to exercise regularly in a warm-to-hot environment and to a point that stimulates moderate to heavy sweating for a period of thirty minutes to one hour, three or more times a week. Indoors, you can simulate a hot environment by wearing more clothing–a sweatshirt and sweatpants, for example.
Start at a level appropriate to your current physical condition (perhaps with advice from your doctor), stay well hydrated, and train for gradual rather than leapfrog improvement. Even two or three weeks of this acclimatizing can be very helpful. What you’re really doing, from a physiological standpoint, is training your body to sweat efficiently. Your sweat response to heat will be quicker and more effective, and your sweat will contain lower amounts of sodium chloride (salt) and potassium. Not only will this help protect your vital electrolyte balance and minimize the likelihood of cramping, it also speeds up evaporative cooling, since low-salt sweat vaporizes faster.
If you are unable to heat-train prior to a hot hunt, you can still acclimate to a degree by pacing your activities and exertion level wisely once you arrive at your destination. Begin with comparatively brief, low-to-moderate exertion-level exposures to hot, bright-sun conditions, resting often (preferably in cooling shade), while also drinking ample water to maintain hydration. Moderately lengthen heat exposure and increase your exertion level each day, unless or until you feel any symptoms of heat strain. If you do, back off a little. Save the hardest and longest hunting days for the latter part of the trip. By then you should be better acclimated to the climate and more able to hunt well and safely in the heat.