"Never be limited by other people's limited imaginations. If you adopt their attitudes, then the possibility won't exist because you'll have already shut it out." -Mae Jemison, astronaut

Wednesday, January 19, 2011

More on Heat Training

It's definitely a topic coming up often in emails and during runs these days. How do we keep up the training in WA's summertime (alternatively, I know people in western Canada right now trying to manage their training in extreme cold and with ice and snow making terrain treacherous for cars and feet alike).

Since I'm here in WA, I'm certainly more focused on how to train in the extreme heat. Questions arise like:

"How do I motivate myself to get out the door?"
"Is it safe to exert myself much in midday heat?"
"Is it counter-productive in any way to train midday or do I need to be going out at 5 AM?"

There are other questions like "Why?" but they can probably only be answered by philosophers.

Well, I found a couple interesting articles today that have helped my motivation. Both of these are from the Journal of Medicine & Science in Sports & Exercise from 2008. If you're not a stats detail person, cut to the chase highlighted in orange. I'm going to start trying to chill my hydration bladder from now on - I never do!

Cold Drink Ingestion Improves Exercise Endurance Capacity in the Heat
Lee, JK, Shirreffs, SM, & Maughan, RJ.
pp. 1637-1644

Purpose: To investigate the effect of drink temperature on cycling capacity in the heat.
Methods: On two separate trials, eight males cycled at 66 +/- 2% VO2 peak (mean +/- SD) to exhaustion in hot (35.0 +/- 0.2 degrees C) and humid (60 +/- 1%) environments. Participants ingested three 300-mL aliquots of either a cold (4 degrees C) or a warm (37 degrees C) drink during 30 min of seated rest before exercise and 100 mL of the same drink every 10 min during exercise. Rectal and skin temperature, heart rate, and sweat rate were recorded. Ratings of thermal sensation and perceived exertion were assessed.
Results: Exercise time was longer (p <0.001) with the cold drink (63.8 +/- 4.3 min) than with the warm drink (52.0 +/- 4.1 min). Rectal temperature fell by 0.5 +/- 0.1 degrees C (p < 0.001) at the end of the resting period after ingestion of the cold drinks. There was no effect of drink temperature on mean skin temperature at rest (p = 0.870), but mean skin temperature was lower from 20 min during exercise with ingestion of the cold drink than with the warm drink (p < 0.05). Heart rate was lower before exercise and for the first 35 min of exercise with ingestion of the cold drink than with the warm drink (p < 0.05). Drink temperature influenced sweat rate (1.22 +/- 0.34 and 1.40 +/- 0.41 L/h for the cold and the warm drink, respectively, p<0.05). Ratings of thermal sensation and perceived exertion (p<0.01) during exercise were lower when the cold drink was ingested.
Conclusion: Compared with a drink at 37 degrees C, the ingestion of a cold drink before and during exercise in the heat reduced physiological strain (reduced heat accumulation) during exercise, leading to an improved endurance capacity (23 +/- 6%).

Thermoregulatory Responses to Constant Versus Variable-Intensity Exercise in the Heat
Mora-Rodriguez, R., Del Coso, J., & Estevez, E.
pp. 1945-1952

Purpose: To compare the thermoregulatory responses between constant (CON) and variable-intensity exercise (VAR) in a dry-hot environment (36 degrees C, 29% relative humidity, and 2.5 ms airflow).
Methods: In a random order, seven endurance-trained heat-acclimated subjects cycled either at 60% VO2max (CON) or alternating 1.5 min at 90% VO2max with 4.5 min at 50% VO2max (VAR). Total work output (915 +/- 100 kJ) and exercise duration (90 min) were identical in both trials.
Results: Net metabolic heat production was not different between trials (394 +/- 12 vs 408 +/- 11 Wm for VAR vs CON). However, heat storage (60 +/- 3 vs 48 +/- 4 W.m), the increase in rectal temperature (1.6 +/- 0.1 vs 1.3 +/- 0.1 degrees C), and final heart rate (HR; 147 +/- 5 vs 141 +/- 4 beats/min) were all higher for VAR than for CON (p < 0.05). During VAR, averaged forearm skin blood flow (SkBF) was lower, whereas whole-body sweat rate (1.23 +/- 0.1 vs 1.11 +/- 0.1 L/h) and dehydration (2.8 +/- 0.1 vs 2.5 +/- 0.2%) were higher than during CON (p < 0.05). Final blood lactate during VAR was higher than during CON (3.5 +/- 0.4 vs 2.1 +/- 0.3 mmol/L; p < 0.05).
Conclusion: Ninety minutes of variable-intensity exercise in a hot environment increases heat storage and fluid deficit in comparison to the same amount of work performed in a constant-load mode. VAR increases not only thermal (i.e., heat storage) but also cardiovasculaar (i.e., heart rate) and metabolic (i.e., blood lactate) stresses, which makes it less advisable than CON when the goal is to minimise physiological stress.

1 comment:

  1. Brings back memories of my sports science days in the 1990's reading these journal extracts.
    Keeping core or rectal temperature low is the key.
    Totally agree with making drinks extra cold beforehand. When I was meter reading I often used to leave a few Gatorades in the freezer the night before. They were frozen solid when I started, but a few hours in the heat, and they were still cold, but ready to drink. Coldness on the carotid artery in the neck and the artery (radial from memory?) in the wrist plus maybe a hat full of iceblocks is another trick I have used, can help with keeping that core temperature down. Skin temperature not as important, but water on the neck or arms seems to make things more comfortable...The hotter it is the more often you need to drink...much to learn on this topic....