prathmann

The drag force of air resistance is proportional to the square of the speed. But the power (work or energy per time) needed is equal to the force times speed and therefore goes as the speed cubed.

Seattle Forrest

Spoken like a true flatlander.

Seattle Forrest

This is why I don't fully trust a power meter over a good, modern heart rate monitor to tell me how many calories I've burned. You rush to the top of a hill, crest it with your HR in Z5, then coast down as you recover; the PM reports no work during the coast but you're actively recovering and it takes energy to do that. Also you're balancing and steering the bike, picking your line, etc; that stuff may or may not burn more calories than standing still, but it burns (slightly) more than zero.

dbc

From a physics point of view, the force applied must be in the same direction of movement to have any "work". So an object at rest, or an object moving on a flat surface at a constant speed (with no friction) both do no work. Your muscles have to work against something to get exercise.

In more practical terms, your body has to spend some base amount of energy to stay on the bike and coast. But you will spend more if you keep pedaling.

DaveWC

Doesn't a Garmin head unit (or other brands for that matter) consider power, HR and speed when calculating calories? Or is there a hierarchy? i.e. when power data exists, use that. If no power, use HR. No power & no HR, use speed.

Sy Reene

And of course you can have a scenario of pedaling and producing no power. Eg spinning at 90rpm in a 34/29 gear while coasting down a hill at 30mph

Seattle Forrest

It's weird. I have two Garmins, an Edge (800) and a Fenix 3 GPS watch which is mostly aimed at hikers (which I am) and triathletes.

On the Edge, I have a screen with kJ and kCal, I don't look at it very often but it's good to know sometimes. anyway, the calories is always a bit more than the work, it seems pretty reasonable.

On the Fenix 3, the kCal it reports is always the kJ. Like instead of converting, it just changes the label. The F3 will use HR if it doesn't have power but clearly uses power and ignores HR if you have a meter.

Seattle Forrest

Little power, not no power.

Doctor Morbius

That's pretty much my take on it too. The work has already been done in order to coast on flat ground, ergo no cheating (his term to mean cessation of calorie burning/exercise). While I agree that I may no longer be droping the hamer at the time of coasting, the workload has already been achieved prior to the coasting segment.

I agree with this too. Riding at a steady speed on the flats (which does require constant pedaling) with little variance is more efficient than speeding up and coasting/slowing down. So a person who does interval training can achieve more actual work, even with a lower average speed, than someone who is riding at a steady pace at a higher average speed.

************

For the record, I pedal most of the time, even when decelerating as it has the added benefit of clearing out waste products. I coast when going around some turns (especially those with low visibility) and when I see potential for mayhem up the road (for example: kids, people backing out of driveways, etc.).

bmcer

I'm none too sure how Garmin head units arrive at the values they do for calories. Not too long ago, I added a Vector PM, but looking back over my ride metrics, as recorded by an Edge 810, I don't see a significant change in recorded calorie output for rides over the same course at the same level of intensity since adding the power data. It's interesting that what the Garmin reports as calories is usually lower than what I get if I convert work (kj) as reported by Golden Cheetah to calories using the more or less standard kj X 1.1 = Calories. In any case, I tend not to pay much attention to calories since different programs often report widely different values for the same ride. On the other hand, work (kj) is pretty consistent across a variety of software, even on the Strava site.

As to the question at hand, I have no idea what the OP's walking friend is getting at. I don't see how the term "cheating" applies in any consistent manner. Coasting does get you some distance for a reduced (but not zero) energy output, but distance alone is a poor measure of the quality of a given session. Just opinion here, but to my way of thinking, work is the metric that most succinctly summarizes the training value of a workout, whether it be riding or walking or whatever. The real difference I see is that for riding, work can be, with the right instrumentation, pretty easily calculated. Doing the same for walking is what might require advances mathematics.

merlinextraligh

I just bought a Garmin 1000. Without using the heart rate monitor, the calories are absurdly high. I averaged 1000 calories an hour on a flat 15mph recovery ride.

With HR data, my understanding is it gets better.

But it still is not as good as a power meter multiplying KJ by 1.1.

Seattle Forrest

Your 1000 with an HRM should get you within 7 % of the golden truth in terms of calorie burn from a ride. According to one of those power meter guys (forget which one) calories from kJ should get you to within 5 % of the truth, but of course that's assuming perfect accuracy from your PM which is probably rated to +/- 2 %.

bmcer

Agreed. And the kj give by Golden Cheetah seems pretty reliable in that the value it produces matches Strava, WKO, and Cycling Analytics pretty closely.

It is interesting to note that the calories calculated by Training Center and Garmin Connect (with HR data) didn't change much at all when I added the PM. It still comes out about 10% lower than using the kj X 1.1 formula with the kj from GC.

merlinextraligh

I don't think Edge uses the power meter data to calculate calories.

Marcus_Ti

Hey now, I ain't one of those Floridian people

The Flattest U.S. States? Not What You Think

Science: Several U.S. States, Led by Florida, Are Flatter Than a Pancake - The Atlantic

bmcer

Merlin,

Based on my experience, I'd be inclined to agree.

McBTC

Cheating connotes a moral issue. Compared to walking, cycling is far more mechanically efficient.

However, I think what your friend actually means has more to do with the quality of the exercise --e.g., he's actually saying something like: you're supposedly out to get exercise but you're only kidding yourself because I get more exercising walking than you get coasting.

Physics won't be of as much use as simply measuring the amount of watts produced for each activity. All we know for sure is that for the same amount of energy it would take to walk a cyclist will cover a lot more ground.

In general I'm guessing that for a given distance, riding a bike requires 1/3 less energy. So if you both workout and your friend walks 3 miles in that time, you'd be getting more exercise (burning more calories, putting out more watts, etc.) if you biked 12 miles and not just 9 miles in an hour.

Seattle Forrest

Didn't read the other one, but this was a lot more interesting than I expected. Nice pics, too.

Seattle Forrest

It's funny how topography can completely change your approach to cycling.

There's a hill about 500 yards from my front door, it gains a few hundred feet over about 2/3 mile. One day a week I do repeats up and down, and almost always coast on the way down. I'm confident this is a good workout, I definitely burn more calories than doing a mostly flat loop around the lake. I've never felt like I was cheating, I'm (1) saving energy for the next lap up, and (2) not going too fast, the location is convenient but congested.

I do agree that a burst of pedaling followed by as much coasting as possible isn't a good workout, it's a hint the rider doesn't have much endurance.

Doctor Morbius

He's not suggesting that I am lacking in moral character. I am, but not because I coast.

He's more or less suggesting I'm a slacker, which I also am, but not because I occasionally coast.

But I coast for the widows and orphans.

Marcus_Ti

The Atlantic article gives a USA map in the header with the top "flatness" ranking for every state which is why I included it...as well as more discussion.

Nebraska actually ranks 20th, middle of the pack as far as flatness goes according to their data. Which, when you have +/-20m or 30m rollers (in addition to the river/creek valleys) at 2-6 percent measured on paved roads with a Garmin (roads in NE tend to follow compass directions rather than the lay of topographic features) seems about right.

Trevtassie

"The power required to overcome the aerodynamic drag is given by:
Note that the power needed to push an object through a fluid increases as the cube of the velocity. A car cruising on a highway at 50 mph (80 km/h) may require only 10 horsepower (7.5 kW) to overcome air drag, but that same car at 100 mph (160 km/h) requires 80 hp (60 kW). With a doubling of speed the drag (force) quadruples per the formula. Exerting four times the force over a fixed distance produces four times as much work. At twice the speed the work (resulting in displacement over a fixed distance) is done twice as fast. Since power is the rate of doing work, four times the work done in half the time requires eight times the power."

The cube means that the power curve is very steep and increases rapidly.

Pedalling and then coasting is very inefficient energy wise.

But in terms of training muscles, constant pedaling is better...

So you both cover 3 miles...if you both average say 2 miles an hour then he'll use much more energy than you. If you average 20mph even with coasting you'll use much more energy than him.

svtmike

I'm not sure I understand the point of picking this nit. As long as you are alive, you're always burning more calories than the power meter reports.

DaveLeeNC

Part of the 'work' being done is to overcome wind and rolling resistance (and in energy balancing accounting, these losses count). While rolling resistance is independent of speed for the most part, wind resistance most surely is not. Everything being the same except speed can make a dramatic difference.

For example, if you were to ride a flat mile on your bike as slowly as you possibly can, you would expend maybe 5000 joules of work and pretty much all of this would be to overcome rolling resistance. Ride that same mile at 25 mph and you are up around 50000 joules of work over that same mile (almost all of it to overcome wind resistance).

Running and walking are much more like riding a bike REALLY slow as the energy expended per mile tends to be relatively constant (but hardly equal).

dave

DaveLeeNC

I don't believe that the BOLD part is correct. A roadie on a decent bike/decent tires is going to burn (metabolically) around 37 kcal per mile @20MPH. I don't believe that an adult of reasonable weight could walk at 37 kcal per mile.

dave