Unqualified Offerings

Unqualified Dog pooped out on this morning’s run so we cut it to an hour and a quarter from a planned 90 minutes. I’d worry - she’s eleven, and she’s been a touch draggy the last few times out - but a similar thing happened last year. We were on our first eight-mile run and she staged a sit-down about two miles from the end. We took a walk break and finished (had to get to the car after all) but Neighbor Q and I both thought “This is her limit” as a running companion. But a week later she made it through eight miles and never lagged again. She topped out, like me, at a 16-mile long run.

On the other hand, she is another year older, and I detected maybe the first touch of arthritis in her over the winter, a bit more effort clambering onto our bed than heretofore. Also, since I get to bike and she doesn’t, I’m getting more total aerobic exercise than she is, so we’re at more risk of diverging than last year, when we shared just about every session.

Today’s general-interest topic is net calories, specifically a myth that I myself always believed about exercise. Perhaps you believe it too: travelling one mile on foot burns 100 calories, regardless of how fast you travel. Walk a mile, burn 100 calories. Run a mile, burn 100 calories. Adjust for body weight, yes, but speed and manner of locomotion can be ignored.

Comes an excellent article by Amby Burfoot in the September 2005 dead-tree Runner’s World to disprove this. First, the mere fact that running entails the extra effort of hopping from one foot to the other along the path from Point A to Point B leads to a greater gross calorie burn than walking. Burfoot cites the thrillingly titled study “Energy Expenditures of Walking and Running” from the December issue of the journal Medicine and Science in Sports and Exercise (Abstract; the full text version is subscriber-only) and the work of David Swain of Old Dominion University.

Long story less long: At a simple level, running burns about 50% more gross calories than walking. Burfoot gives the formulae as

Running: 0.75 x weight (pounds) x miles

Walking: 0.53 x weight (pounds) x miles

That’s total calorie burn. But if you’re a walker, it gets worse. Because what you really care about is net calories, the calories you burn over and above what you’d have burned just sitting or standing around. Walking takes longer. Burfoot gives the following net calorie formulae:

Running: 0.63 x weight x miles

Walking: 0.30 x weight x miles

These formulae have to be approximations, since your basal metabolic burn (what you’re subtracting from total calories) should be constant over time, so the faster you run (or walk) the higher your net calorie usage, because you cover more ground in the same unit of time. Today was an easy run day for me, so I went quite slow. People who covered the same distance in less time should have a higher net calorie burn than I did.

As a general trend, though, it’s reasonable to say that running burns about twice the net calories per unit distance as walking. Very approximately, walking burns around 50 calories per mile, and running around 100. And since a trained runner can cover at least twice as much ground in the same time, running is about four times as efficient at burning calories as walking is.

The numbers for me (180# shod and clothed) on a five-mile run versus a five-mile walk:

Run: 0.63 x 180 x 5 = 567

Walk: 0.30 x 180 x 5 = 270

Who burns exactly 100 calories per mile? (I mean “exactly approximately?) Someone who weighs 159 pounds.

Why does it matter? The distinctions between walking and running and between gross and net calories risk bedeviling people trying to control their weight through exericise. For instance, Mrs. Fields tells me that her delicious Chewy Fudge cookies average 260 calories. a 150# woman who thinks she’s paid off that cookie with a two and a half mile walk is almost 150 calories short of where she thought she was. A 180# man who, oh just as an example, hops on the exercycle until it says “260 calories” will also come up short if the cycle’s calorie reading is gross rather than net. (I’m guessing 50-100 calories.) I spent much of last year (and this) thinking I was burning about 20% more calories than I should really have credited myself with.

If you want to get super exact, you need to get into METs and oxygen consumption since, as Burfoot quotes Swain in the article, “When you perform a continuous exercise, you burn five calories for every liter of oxygen you consume.”

Final wrinkle: Burfoot avers that at very race-walking speeds - 5-5.5 mph - walking burns more net calories than running. That’s all very nice, but what I’ve noticed out on the paths of suburban Maryland and DC is that hardly anybody really race-walks.

This week’s training dept:

Monday, 45-minute stationary bike at 131 bpm pulse rate
Tuesday, 45-minute conversational-pace run
Wednesday, 45-minute stationary bike at 131 bpm pulse rate
Thursday, strength routine (Fitzgerald base phase) and swim lesson/exam
Friday, core-training routine and 1:00hr conversational-pace run
Saturday, 1:15hr bike trip
Sunday, 1:15hr conversational-pace run

Next week: low heart-rate endurance training, an introduction.