I was going through some old threads on letsrun when I came across this post from Dr. Daniels related to heat training and heart rate. I have head a lot of people talking about how bad their running is in the summer, and have felt the effects myself, so I thought that I would throw this up here as food for thought.
“You are experiencing one of the flaws of getting too dependent on HR. The same VO2, same intensity of effort on the total body as it relates to your running, and blood lactate accumulation will be associated with different HR, which is quite dependent upon the weather, as you have experienced. If you follow HR then you are focusing you interest on HR stress and not on total stress. Heat will slow everyone down in the marathon — some more than others because of how they are affected, individually. So, you don’t have to back down your pace becasue your HR is higher than usual. Keep in mind that the work your heart does is a function of the resistance against which it pumps and the force of each stroke. When blood volume goes down, so usually does blood pressure and so does stroke volume. So even though you may have a faster HR the heart muscle may not be working any harder — faster per beat, but less work per beat. As long as you are healthy, and it would seem you are, then go more by feel than HR. What heart-rate monitors are good at is they tell you how fast your heart is beating; pretty simple”
And here is another post from a different thread:
Some things to note about the heat and humidity?
The first thing is dehydration. You lose water and you body can’t function correctly. Ph values get out of whack and heart rate increases do to lower stroke volume.
The second is that your body cannot cool itself in humid conditions because the air is already saturated. The desired effect of sweating is for the sweat to evaporate and cool you upon the phase change to a gas. That doesn’t happen in humid conditions.
Your body reacts to heat training by increasing blood plasma volume to have more stored water for cooling.
Training in the heat helps you train better in the heat but not necessarily run faster.
Heat will limit both the duration and intensity of any given aerobic run.
A third big variable that people over look is that training in the heat is that it is basically the same as training at altitude. There is less oxygen in the air on a hot day. There is even less air on a hot, humid day. This is a fact. Airplanes need more runway to take off on hot days, and golf balls driven further from the tee because there is simply less air.
At first glance you might say aha! Altitude training that’s great!
But altitude effects are due to a constant stimulus. Much like gravity is a 24 hours stimulus?the same is true for altitude. So in true altitude you are literally training in your sleep. But in the heat the stimulus disappears the minute you step into air conditioning. So in the heat you get the worst effects of altitude and none of the benefits.
I?ve run the numbers before and figured that a hot humid day (sea level, 85F, 90% humidity) is about the same as a cool morning in Denver (5200 ft, 35F,90% humidity) as far as oxygen content is concerned.
Figuring the heat part is easy. Oxygen content is an inverse linear relation the temperature. Higher Temp = Lower Oxygen.
For the humidity you need to consult the non linear psychrometric charts to determine thermodynamic properties of moist air. This is necessary to assess the humidity ratio as a function of temperature. Humidity ratio is simply an absolute measure of how much water vapor is taking up space in the air. It is not the same a relative humidity. Changes in relative humidity mean very little in cool temperatures because the air cannot hold water. But on warm days, relative humidity means everything because vapor is able to HOG up space in the air much more. So it is easy to feel the difference between 90% and 50% humidity on a warm day. But on a cool day it is not as easy to detect. The bottom line is that on warm days high relative humidity means far less oxygen.
Driving pressure makes a difference. Oxygen content has a direct linear relation to pressure. Higher pressure = Higher Oxygen. Higher barometric pressure can drive more oxygen into your lungs. High pressure occurs after a cold front passes through. Low pressure occurs during rain?or at altitude. As you go higher there is less pressure. This is why the captain pressurizes the cabin in an airplane. It is also the dominating effect on oxygen at altitude.
So we are really looking at 3 critical variables for oxygen content: Temperature, Humidity, and Pressure.
An optimal day would be cool and crisp at sea level with high barometric pressure aloft (cold front).
The worst day would be hot humid with at altitude with low barometric pressure aloft (storm system etc.).
A fourth issue to be concerned about is the actual sun?s rays hitting you body. This allows you body to ?cook?. Similar to a green house?the sun?s energy hits your skin as radiation and then it converted to heat…but your body can?t dissipate it because your sweat can?t evaporate. So your core temperature rises dramatically. A warm 85F in the sun is not the same as 85F in the shade or low intensity rays. So seek shade whenever possible. Don?t use oil sun screen either or you will really cook. One way to increase cooling/evaporation ability is to run where there is a breeze. But in the summer this can be tough to find.
Gases such as oxygen are not able to be absorbed/soluble as higher temperatures. This could affect the diffusion and transport process of oxygen through the lungs to red blood cells?or other areas in demand if you are over heated.
The bottom line is that if you are training for volume then heat is not optimal. The other issued is velocity. In any quality effort beyond 5 minutes length you really cannot take the time seriously in the heat. It means nothing. So you must train more by “feel” in the heat on quality days. Eventually that becomes a problem because especially near race time, hitting correct velocities is critical from a neuromuscular standpoint.
You must also train slower in the heat even on easy runs so your average velocity drops too. That’s not good either. Perceivably if you try and hold to the same faster paces you could you on cool days, then you could slow up recovery too. I’ve seen people use heart monitors in the heat with some success to keep easy days easy…but the pace sucks.
Repetition and short speed sessions work out just fine in the heat. Just stay hydrated.
So people in cool climates are able to train more volume, at a higher average velocity and recover better. Sounds like a good deal doesn’t it?
Bottom line for best performance…move to San Diego. Or Bolder or Flagstaff. But probably San Diego.