Monday, December 31, 2007

Scientific Evidence Suggests I'm a Wimp

I've written several times about my desire to acclimate to cold weather. I ran across this paper:

Prevention of Cold Injuries during Exercise - American College of Sports Medicine

It provided some interesting background on the physical responses to activity in cold temperatures. Here's what I found most interesting:

  • Cold exposure causes an increase in metabolic heat production (burns more calories), but only through shivering. The reviewed evidence does not show a nonshivering thermogenesis (production of heat) in humans. Meaning, unless you are shivering, exercising in the cold does not consume any additional calories.

  • "Athletes exposed to cold weather may acclimatize but the physiologic adjustments are very modest..." In other words, it does not get PHYSICALLY easier to withstand the cold with exposure. Mental aspects of cold tolerance are not discussed in the paper. But, I suspect that my lack of cold weather tolerance is mostly (if not completely) mental. Confirmed, I'm a sissy when it comes to cold.

  • Table 2 shows hypothermia symptoms begin at a core body temperature of 95*F. This is where maximal shivering occurs. By the time your core temperature reaches 89.6*F you are in a stupor. Despite my discomfort and feelings of being cold, I've never even reached the point of shivering during a ride. So why I may have felt cold - my body has not shown even a minor response. I'm not physically cold.

  • "Exposure to cold air ... may also increase urine flow rate, the so-called cold-induced diuresis (CID). This response is likely caused by a redistribution of body fluids from the periphery to the central circulation as peripheral vascoconstriction occurs." I've observed this, but attributed it to lack of sweating.

  • "Lastly, even healhty persons can experience an increase in respiratory passage secretions and decreased mucociliary clearance when breathing very cold air during exercise." I've certainly noticed this condition!

Summary, I need to focus mind-over-body on the next cold weather training ride! I'm actually looking forward to see how I handle it.