Heat slows you down because your body uses your blood supply to cool off, thereby reducing the blood supply for your muscles and other functions. In addition to sweating, when we overheat blood is sent to our skin to act as a heat exchanger. This is why a cold towel on your neck helps cool you off and feels so good when you are overheated. Your neck becomes a heat exchanger and the cool towel increases the efficiency of transferring heat. Water is six times more efficient than air at transferring heat.
Your body will acclimatize to heat over time – but this takes up to two weeks. Your body increases your efficiency by building more red blood cells so you can have a bigger heat exchanger.
When you get hot humping up a steep mountain with your backpack there are suddenly three demands on your blood supply. First, your muscles are screaming to get oxygen, fat and glucose so they can do their job of motion. You are breathing harder and your heart is pumping faster. Your cardio vascular system needs increased oxygen and calories also. Now throw in the cooling effect of blood to your skin to heat exchange and your blood supply becomes overloaded. If you have food in your digestive track, this creates additional demand on your limited blood supply. At times the only answer is slowing down when it gets too hot.
Anything you can do to help your body cool down will reduce the competition for blood supply and help you keep your pace steady.
- Shade from a hat or umbrella.
- Wet your hat down and let the water evaporate.
- Drape a wet towel or kerchief on your neck. It is very effective and feels really good.
- Cool as much of your body as possible in any water supply.
Hiking out of Palm Springs, Mission Creek was our savior on a 90+ degree day. We headed out with full packs and six thousand feet of elevation gain ahead of us. We could not drink enough to stay cool or hydrated. We doused ourselves with creek water every time we got a chance passing near the creek in the exposed desert terrain. It was a saviour. By nightfall we had made it twenty-five miles to higher cooler elevations.
We used half strength gatorade (from powder) and Nuun tablets. We found half strength gatorade was enough to keep our electrolytes up, increase our carbo calorie count and keep us interested in drinking enough water. Nuun has considerable variety in their flavors, and even some with caffeine which has its attributes. The key to hydration is to use the technique and flavors that keep you drinking enough to avoid dehydration. Experiment and figure out what works for you.
Eat plenty of foods with salt and electrolytes. Most energy bars have a good mix. If its super hot and you are burning through liters of liquids and heavily sweating you can also use salt pills as ultra athletes do for endurance events that last all day — similar to an all day hike.