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Very interesting reading..I have been following this post. Does anyone know if you burn more calories walking at say an elevation of 6300 feet..compared to sea level? Was just curious about that. Thank you for starting this post

The extra work of breathing thinner air at any altitude does require some more calories. How much?

From Hultgren's text High Altitude Medicine: At sea level, breathing normally uses only 1-2% of total oxygen (and calorie) consumption, rising with exercise to perhaps as much as 13% of VO2Max

The next comments are applicable not to your 6300 feet, but to extreme altitudes where ventilatory rates and pulmonary fatigue are exaggerated. There, oxygen (and calorie) cost of just breathing and staying alive becomes a much higher percentage of the total. Part of this is the act of labored breathing and part of it is sucking in dry subzero air and exhaling it an extra 100+ degrees F and 100% humidity. That takes a furnace.

Hultgren says that on the summit of Everest and breathing ambient air, the cost of breathing AT REST (once you get there) is no longer the small amount as it is at sea level,but as much as 50% ,leaving little reserve for locomotion. That's why ascent rates creep to only 200 vertical feet/hr at that altitude, turning many a climber back within tantalizing sight of their goal.
pant, pant... Harvey

For obvious reasons, it isn't easy to design studies to answer those type of questions (what is the work of breathing at altitude, what is the peak VO2 at altitude). There are a few studies that have tried to address these issues, though I apologize for the gibberish jargon that follows ...

Cibella, et al ("Respiratory energetics during exercise at high altitude", J. Applied Physiology. 1999;86:1785-1792) estimated it to be 5.5% of the peak VO2 at sea level and 26% at altitude (5050 m). Granted, he only had 4 subjects ... but it's one of the better studies to address that question.

On a purely semantic note, the estimation of basal oxygen uptake equaling 50% (or thereabouts) of peak VO2 at the summit of Everest is for those who are fit enough, have the appropriate physiologic responses to altitude, and are lucky enough to get to the summit. The mere work of breathing and basal requirements at extreme altitude likely greater than the max VO2 (at altitude) for the majority of folks incapable of achieving those sorts of altitudes.

To put things in perspective, during the American Medical Research Expedition to Everest (AMREE) in 1981, West and colleagues estimated the peak VO2 of some of the climbers to be 1.07 L/min (15.3 L/kg/min) while at 6300 m and breathing 14% FIO2 to simulate the partial pressure of O2 at the summit of Everest ... compared to 4.63 L/min (61.3 L/kg/min) at sea level. (West, et al. JAP 1983;55:678-687 and JAP 1983;55:688-698)

Hope this helps ...

Runnersworld.com moved the link on me!

Here is the updated link that addresses the question: How many calories are you actually burning?

http://www.runnersworld.com/article/0,7120,s6-242-304-311-8402-0,00.html

Thanks

Thanks for the updated link.

It is interesting to note that Amby Burfoot, who wrote the article, mentions the change in mechanics as the apparent reason for the HR for walking passing the HR for running at speeds above 5 mph. Given that he was the only one in this self-experiment, we can probably safely say that the 5 mph crossover point only holds for him, and that the crossover point will be different for each individual and depend on such variables as stride length, stride frequency, flexibility, center of mass, and individual mechanics.

In terms of calories burned at altitude, remember that heart rate (HR) will by and large indicate the amount of work i.e. calories burned, so that a HR of 150 at sea level and a HR of 150 at 6300 ft. means that you are burning the same amount of calories for a given time period at these elevations. Remember also that your heart rate even at rest increases when going up to altitude, indicating that your resting metabolic rate is higher at altitude than at sea level, and that walking at 3 mph on level ground at altitude will be harder than walking 3 mph at sea level. This will be indicated by a higher HR, which means you are working harder and thus burning more calories trying to maintain the 3 mph compared to what it would take at sea level. At extreme altitudes, there is the possibility of a blunting of the HR response due to neuroendocrine changes in the brain, such as may occur in the so-called "Death Zone",but for the purpose of the altitudes most of us are hiking in, the HR-work relationship holds.

As mentioned before, there is ~50% reduction in VO2Max at an altitude of 6000 meters compared to sea level, meaning that the maximum oxygen your body can take in is about half of what you can take in at sea level. Remember that this is an average; individuals may vary. Interestingly, it has been shown that the higher your VO2Max, the greater the % drop in VO2Max! Theoretically, this may mean that at a certain altitude, people of a certain mass may all have an equivalent VO2Max (a victory for couch potatoes!)

Some other interesting notes:

Studies on Pikes Peak have shown that, at least at that altitude (~14,400) The first 9 days of acclimatization are primarily ventilatory, or breathing related, in nature. After that, any further acclimatization is Haematologic i.e. blood related.

Glucose Tolerance has been shown to improve at altitude. This may have implications for those trying to control their blood sugar levels, such as diabetics.

As the body adapts to altitude, there is less reliance on glucose during exercise. Interestingly, women appear to rely more on fat as an energy source at altitude than men. This mirrors similar studies at sea level.

It appears that madeintahoe asked her question because she lives in Lake Tahoe at an elevation of approximately 6300'. (Just a guess.) So she is apparently well acclimated to that altitude, unlike hikers who go up from low elevations. For a person who lives at 6300' it seems that she is burning calories at very close to the same rate when walking at 6300' as she would burn if she lived and walked at sea level. Is this correct?

Bob, per Clinton, it depends on what your definition of "very close" is is.

I don't think 6300ft is enough altitude to require extra respiratory effort (and fuel/O2 consumption) to allow obese people to lose weight overnight (the gold standard as promised on TV). 6300m yes, 6300ft, nah, only just a mathematically minuscule amount, not worth all our talk.

-The transition point from walking to running has a very small tolerance. It is close to 5 mph for all individuals. Continuing to force one to walk past this point disrupts biomechanics, is inefficient compared to running, and thus requires more energy to maintain.

-Heart rate does not dictate the number of calories burned and an increased RHR does not indicate a higher resting metabolism. People who are out of shape, overweight, or otherwise unhealthy have high resting heart rates. They do not have higher resting metabolic rates. For example: my resting heart rate is between 35-40 bpm. My resting metabolic rate (calculated in an ex phys lab) is 22% higher than average.

Higher resting heart rates at altitude are caused by a lower PPO and mediated by oxygen-sensing systems in the pulmonary artery, carotid body, and rostral ventrolateral medulla.

-Although individuals with higher VO2maxs may have a greater absolute decrease in their VO2max at altitude, when compared to a person with a lower V02max, they will still work at a lower percentage of their V02max at any given workload. Therefore, they will still have an advantage over the couch potatoes.

I just talked to a woman who walks at 5.8 mph and is not racewalking, and is about 5'7". I have watched her in the gym, so I was curious as to her speed. My guess is that a very short person is going to have real problems getting close to 5 mph compared to a person who is quite a bit taller than average, and may be able to walk faster due to a greater stride length; this has been born out by people that I have worked with over the years.

It is true that RHR is not correlated with metabolism, for reasons mentioned in the previous post. When we calculate a training heart rate range for a client (given that it has not already been done in an exercise physiology lab) we use what is known as the Karvonen formula. This formula takes into account the RHR of the individual, and is far more accurate in calculating %VO2max than the method used on most of the aerobic equipment found in the gym. The formula is (220-age-RHR)x %VO2max + RHR. Thus if you wanted to exercise between 70 and 85 % of your VO2max you would do two calculations, one with 70 and one with 85 in the %VO2max space to get your training range. This has been shown to correlate well with actual VO2 measurements in numerous studies.

Resting metabolic rate is determined by many things, among them lean body mass and various genetic factors. Unfortunately, average in this country is not that great. It would be interesting to get some measurements on some of the members of this forum!

Interestingly, it has been shown that SaO2 levels in those of Tibetan ancestry, such as Sherpas, is higher than it is in other ethnic groups, even if the individual was born and raised at lower elevations, thus meaning that they are able to absorb more oxygen from the lungs for use by working muscles, even under conditions of low oxygen tension. More specifically, more oxygen is bound to the haemoglobin in the blood.

As for the couch potatoes, I guess they're on their own, at least when it comes to mountains on earth. Maybe Olympus Mons on Mars.......

Yikes!! Most of this is a bit over my head with all the formulas and stuff..But still very interesting. Bob K. yes you are right I do live at 6300 feet and have for 20 years now..so I was just kinda wondering and curious about it.. I do realize that 6300 may not be enough for it to make a hugh difference..But living at this altitude I do feel it has helped me acclimate a bit better when im over 10K and above.

ExPro...interesting about the stride length..Im 5' 10" so I should have a longer stride...I never really paid to much attention to it. The women that you meant..do you know if she is walking that on a flat road?
Thanks again everyone for all this info

Madeintahoe;

The woman was actually walking on a treadmill, which is going to be a little easier than walking outside. Your natural stride length may be more influenced by such mechanical factors as leg length and flexibility of the structures around the hip, such as muscles and ligaments. Nevertheless, a longer stride length can be trained for; athletes in a number of different events work on increasing stride length. Of course, a long stride length in and of itself doesn't necessarily mean your going to be fast; the other variables play into it as well. There is a certain 4'11" hiker that you have hiked with that seems to do pretty well for herself!

For what it's worth, the world record for the women's 20 km walk is 1:25:41, which represents an average of 8.7 mph for 12.4 miles.

Now, that *is* race walking!

To digress a bit, I thought you might be interested in Robert Barclay Allardice, who on bet walked 1,000 miles in 1,000.

http://www.answers.com/Robert+Barclay+Allardice?gwp=11&ver=1.1.0.364&method=3

Feats of pedestrianism
In 1801 Captain Barclay walked 110 miles (177 km) in 19 hr 27m in a muddy park
In 1802 walked 64 miles (103 km) in 10 hours
In 1805 walked 72 miles (116 km) between breakfast and dinner
In 1806 walked 100 miles (161 km) over bad roads in 19 hours
In 1807 78 miles (125 km) on hilly roads in 14 hours

ExPro..Thank you..yes a treadmill....I kept thinking that is darn fast walking if she was walking outside on the road. I have been trying to walk everyday...but it's hard to pick up any speed because the roads are really icy in places & you have to be very careful walking so you do not slip....I need to do more snowshoeing instead! Yeah my friend, she is an awesome hiker for sure

When it comes to bipedal locomotion, research has shown that efficiency is maximized by increasing stride frequency not stride length. In a competition or survival situation you want to be as efficient as possible. On the other hand, one would not want to be "efficient" if the goal was to lose weight.

Unrelated to this subject; the opposite applies to swimming. Efficiency is maximized by lengthening the stroke and decreasing the stroke frequency. This is due to water resistance. A longer vessel (body or boat) experiences less resistance in the water.