Otisbean and I dialogued about some of the problems regarding injuries. If you are interested, you might want to review our handful of posts beginning at #614 in the
Re: Training Camp Practice Updates thread.
I’ll try to give you somewhat of an overview to what I think should answer some of your other questions.
Humidity is not your friend The rate of sweating is higher in humid conditions but the cooling is less. The reason is that because the air is already very saturated with water, sweat can't evaporate. Sweat that beads up and rolls off doesn't function in the cooling process. However, this what we call "futile sweat" does deplete the body of vital water and salt. As dehydration progresses cooling becomes more difficult. Performance drops and heat injury becomes a real threat. Deaths have occurred when the air temperature was less than 75 degrees F (24 degrees C) but the relative humidity was above 95%.
Adapting to the heat, one tried and true piece of advice is, "Make no new changes on game day". The same applies to environment. Heat acclimatization is a process by which the body makes adjustments to promote better cooling in hot environments. Sweat becomes more dilute. The threshold at which sweating begins is lowered and the sweat rate is increased. These, and other, changes take time to fully complete -- about 10 days of exercise in the heat -- and will only work if you are well hydrated.
Some medications interfere with cooling Certain drugs may cause dehydration or interfere with sweating. Antihistamines and some blood pressure medications decrease sweating. Caffeine and alcohol are diuretics and thus cause your body to lose water. You should avoid their use for several days prior to the practice/game. I will make book with you that many of the players love their alcohol too much to adhere to this simple restriction......and they eventually pay for it.
Hyperhydration just before the start of practice or game becomes important. Drinking approximately 400 - 600 ml (13 - 20 ounces) of cold water or an electrolyte solution can help delay the process of dehydration.
It may seem obvious to drink during the practice/game, but many people underestimate the magnitude of their fluid loss. It is very difficult to avoid dehydration during especially the longer game in the heat because the rate of sweat loss usually exceeds the rate of absorption of ingested fluids. The maximum rate of fluid absorption by the gastrointestinal (GI) tract during exercise is approximately 800 ml per hour (27 fluid ounces/hr). The rate of fluid loss through sweating may average as high as 1.5 - 2 liters per hour (50 - 68 fluid ounces per hour). Thus often, despite the best fluid intake, dehydration will occur. For some people, drinking a lot causes discomfort and a feeling of being "bloated". Thus guzzling a liter once per hour will likely cause problems. Also realize that the more dehydrated you get the harder it is for your GI system to absorb what you drink. Dehydration also causes a variety of GI symptoms (nausea, cramping, and diarrhea).
Type of replacement drink is also important. Carbohydrate content in the range of 4 - 8% is best. Levels above 10% are poorly absorbed and can cause diarrhea. Most sports drinks have a sodium content in the range of 10 - 20 mmol/liter (Gatorade is 23 mmol/liter = 1.3 grams of salt per liter). Higher levels are better for salt replacement, but tend to be less palatable. There doesn't appear to be any advantage gained from adding other electrolytes (e.g.. potassium, magnesium) since the diet is usually adequate to replace these.
Salt replacement is important. Sweat contains between 2.25 to 3.4 grams of sodium chloride per liter. A sweat rate of 1 liter per hour would thus cause a salt loss of 9-12 grams for a 4 hour game. Failing to replace salt during the race can result in hyponatremia (low salt concentration in the blood). It is also advisable to increase salt intake for several days before an actual longer game (as opposed to shorter practice).
Another important principle. The higher the intensity of exercise the greater heat production by the muscles. Overheating causes more sweat production.
Personally, I find it difficult to understand the need to be practicing in extreme heat and humidity, except for the 10 days to two weeks before ONE game that will recreate those conditions , such as the Miami game.
Bottom line is that excessive heat and humidity even with best attempts at compensation are likely to affect changes that will lead to FATIGUE, foggy brain, muscle group strength imbalance and function changes, GI problems.......all of which contribute to neuromuscular discoordination (where the brain interacts with the muscles abnormally)...........and higher incidence of injuries.
I will leave you with this thought from my one of my previous posts:
Not to answer for Otisbean, but when you lose overall body energy (total body fatigue), you lose some neuromusclar COORDINATION. This type of discoordination can lead to all sorts of muscular injuries.........with the muscles yinging when they should be yanging.
[Keep in mind that muscle problems can easily lead to any of the other serious injuries such as ligament and tendon tears/ruptures and fractures.]