I make walks to try to keep a little fit and to burn calories/fat. At a temperature of about 16°C I can walk 10K in just above 2 hrs with almost no rest and not being excessively tired afterwards.
I often spend time in tropical countries. At a temperature of 25° and moderate humidity, my performance is severely limited. I would guess that I walk about 3K in 2 hrs and I get really tired. (I try to supplement fluid and electrolytes, of course.)
The actual temperature may also be higher than 25°, I think. I get the temperature readings from the Internet, and I think they usually indicate temperature in the shadow. However, taking walks you are most often in the sun.
I am a Western guy about 175 cm/83 kg.
My question is divided in two:
- How many calories are expended in the two situations respectively? (Brisk 10K walk at 16°C or slow 3K with several breaks at 25°C, being much more tired after the latter. Both take about 2 hrs.) (The first would be about 600-700 kcal, but how much is the latter?)
I refer to EXTRA calories expended by the walking. I have not included the basal metabolism in the figure 600-700 kcal. One may also have to consider change in basal metabolism due to f.ex extra work like sweating needed for heat dissipation.
- If the calorie consumption is much lower in the "hot" alternative, how should you then make your aerobic exercise in the tropics? Is the only alternative to buy a membership with an air conditioned gym and do treadmill etc?
The only thing I found on the Internet is that you burn more carbs (cp to fat) during exercise in hot climate. That may speak against exercising in hot climate, but my guess is that it is just a marginal factor in my situation.
My aim is to burn about 600 kcal extra. I do that in the "temperate" alternative with a 2 hr walk, but how do I do that in the tropical climate?
(OK. I know one answer is "Get up in the morning, you lazy guy." But early or late exercise is just not possible right now for me.)
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2375553/#!po=5.55556 This article mentions thermoregulatory vasodilation in skin as a main mechanism for getting tired more quickly in a hot climate. Cardiac output (f.ex monitored by heart rate) must be used to both muscle and skin. If this was the only mechanism limiting your capacity, I guess one would assume that cardiac exercise could be OK in hot climate but calory burning not necessarily the same when blood is shunted through skin for thermoregulatory purposes.
A useful, non-invasive method to investigate calory burn is indirect calorimetry (IC). (Measure O2 and CO2 in expired air to calculate calory burn pretty exactly.)
I haven't found any studies yet that do IC (and work load) in a hot environment and compare to a temperate environment. One may make the assumption that "blood is simply shunted through the skin to cool off" but to be sure you need experimental data. (Some cooling mechanisms may consume calories, f.ex.)
For example. If you feel "completely wasted" just walking slowly in a hot environment, would your pulse rate then be at the same level as it would be in a temperate environment, for the same level of pronounced "tiredness"? I am not sure the limiting factor is cardiac output, at least not for me. Last time making a walk in hot climate, feeling very weak in the legs, pulse was only around 108 and no real shortness of breath.
Many individual aspects also come into the picture. A short (having the same proportions) or a skinny person will dissipate heat more efficiently. A person with black skin is better protected from UV-rays, but may absorb more heat, under some conditions at least.
This year the L.A. Marathon was run in 31°C heat. Daniel Limo won on 2:10:35. His personal best is only slightly better than that: 2:08:39. As a Kenyan marathon runner he is probably extremely well adapted to heat (genetically and through training).
This good performance in hot weather is interesting. His body can not have wasted a lot of cardiac output by shunting blood through the skin for cooling. I wonder how he performs in cold weather? He maybe has to wear extra clothes when racing at lower temperature??