runnermtl saidHi Guys, I wonder if anyone else is training in "extreme" temperatures? I went for a run today (-12C / 10F) and noticed, as usual, that my heart rate seemed very high for the effort I was putting into it (speed+incline) compared to track running indoors or our mild summer. Does temperature affect heart rate and if so, does it affect the effectiveness of your training overall?
So here's the 'technical answer':
This is analogous to something called the cold pressor test (http://en.wikipedia.org/wiki/Cold_pressor_test), which involves how your body reacts to cold. When exposed to cold, your vasculature begins to vasoconstrict in the periphery, which is a fancy way of saying that it redirects blood to your core to preserve body heat. As a result of this, your body will have an increased afterload (the pressure in the aorta that the heart has to pump against) and an increased pulse pressure (the difference between the two #'s when you get a blood pressure taken). This is just from the regular cold.
Now we add in exercise to this cold weather. Like all other exercise, you're body is trying to increase cardiac output (the total amount of blood pumped by the heart in a min). There are only 2 ways to do this. One is to increase the amount of blood per pump, which is hard for the heart to do since the afterload is already high (you're pumping against a higher pressure). Two, what the body does do, is to increase the heart rate. This helps the body increase cardiac output.
The reason that HR doesn't go as high (usually) during normal temperature exercise is that the body can dilate venous lakes in the skin, allowing more blood flow to the skin and more heat to be lost. When this happens, the size of the whole blood vessel system in aggregate increases and the vasculature can operate at a lower level of pressure. Because the pressure is lower, the afterload is lower, and now the body can compensate by increasing the amount of blood per pump and the heart rate, instead of only being able to change the heart rate.