The gym has machines by pulsefitness.
There seems to be a mismatch in the numbers displayed.

After a bike session the summary was:
Power average: 74 Watts.
Time taken: 9 minutes.
Energy used: 50 kcal.

The above energy figure would equate to 333 kcal per hour.
But 100 Watts is only 86 kcal per hour!

The mismatch is so enormous that I feel I must have missed something.
I would be grateful to any physicist who can shed light on the figures.
--
Chris

Chris wrote:
The gym has machines by pulsefitness.
There seems to be a mismatch in the numbers displayed.

After a bike session the summary was:
Power average: 74 Watts.
Time taken: 9 minutes.
Energy used: 50 kcal.

The above energy figure would equate to 333 kcal per hour.
But 100 Watts is only 86 kcal per hour!

The mismatch is so enormous that I feel I must have missed something.
I would be grateful to any physicist who can shed light on the figures.
Presumably there is some assumed efficiency coefficient in use?

On Mon, 17 Mar 2014 20:09:46 +0000, Chris wrote:

Power average: 74 Watts.
Time taken: 9 minutes.

1 watt is 1 joule/second.

Google "(9*60)*74 joules in kcal"
Gives 9.55 kilocalories.

Energy used: 50 kcal.

Something ain't right. B-)

--
Cheers
Dave.

On 17/03/14 20:09, Chris wrote:
The gym has machines by pulsefitness.
There seems to be a mismatch in the numbers displayed.

After a bike session the summary was:
Power average: 74 Watts.
Time taken: 9 minutes.
Energy used: 50 kcal.

The above energy figure would equate to 333 kcal per hour.
But 100 Watts is only 86 kcal per hour!

The mismatch is so enormous that I feel I must have missed something.
I would be grateful to any physicist who can shed light on the figures.

I think the 74 watts is power output (as developed in the machine doing
the measuring) - and the 50 Calories is the amount of bio-energy burnt
to develop that.

In this example, you have developed 9.5 Calories (or kcal) at the
expense of 50, so about 20% efficient.

Whilst I have no idea for sure, that seems believable for a biological
process.

On 17/03/14 20:09, Chris wrote:
The gym has machines by pulsefitness.
There seems to be a mismatch in the numbers displayed.

After a bike session the summary was:
Power average: 74 Watts.
Time taken: 9 minutes.
Energy used: 50 kcal.

The above energy figure would equate to 333 kcal per hour.
But 100 Watts is only 86 kcal per hour!

The mismatch is so enormous that I feel I must have missed something.
I would be grateful to any physicist who can shed light on the figures.

You have missed the fact that ,mots people know how long 9 minutes is,
and roughly how much power a cyclist produces.

They are also familiar with how many calories they had for breakfast.

But not the conversion between them

So to the average punter 'hey I pedalled hard enough to light a 60W
lightbulb, and burn off three English breakfasts' will make them feel
good and come back.

To tell them they didn't even burn off a slice of dried toast is simply
bad salesmanship.

Cui Bono?
Follow the money.


--
Ineptocracy

(in-ep-toc-ra-cy) €“ a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

On Mon, 17 Mar 2014 20:09:46 +0000, Chris ] wrote:

The gym has machines by pulsefitness.
There seems to be a mismatch in the numbers displayed.

After a bike session the summary was:
Power average: 74 Watts.
Time taken: 9 minutes.
Energy used: 50 kcal.

The above energy figure would equate to 333 kcal per hour.
But 100 Watts is only 86 kcal per hour!

The mismatch is so enormous that I feel I must have missed something.
I would be grateful to any physicist who can shed light on the figures.


At an average power output of 74 watts for 9 minutes duration (the
readily measurable quantities) you will have produced just short of
40Kj of electrical energy. Dividing this by the 4.2j per calorie
conversion factor gives just under 10 Kcalories of energy output from
the generator.

Unless the wattage is an actual wattage output figure on a generator
used to provide the required physical workload and the figure for the
"energy used" is a derived figure for the total energy consumed by
your body[1] to achieve that electrical output, the figures don't make
any sense.

[1] The mechanical losses between the pedal crank and the electrical
output of a generator are unlikely to exceed 15 to 20% unless it is a
spectacularly inefficiently designed transmission system. Even when
coupled coupled to a low efficiency generator (less than 80%
efficiency) you'd still expect the gross mechanical energy input to
stay below the 20Kcalorie mark.

There are additional 'parasitic' sources of energy consumption above
and beyond the useful pedalwork power being transmitted into the pedal
crank (pumping losses, heart and lungs, and other muscular activity
such as in the arms and torso) which can be derived from a lookup
table of previous 'calibration runs' created by the exercise bike
manufacturer using standard metabolic monitoring and measurement
instrumentation on a representative sample of 'volunteers'.

I'm surmising that the average electrical power output and the
duration may simply be the basis for calculating a total metabolic
energy expenditure figure with a reasonable level of accuracy.

You'd have to ask the gym operators about this or get hold of
information from the exercise bike manufacturer (possibly mentioned in
the user guide and/ or on line if the manufacturer has a web page
offering such support).
--
Regards, J B Good

In article ],
Chris ] writes:
The gym has machines by pulsefitness.
There seems to be a mismatch in the numbers displayed.

After a bike session the summary was:
Power average: 74 Watts.
Time taken: 9 minutes.
Energy used: 50 kcal.

The above energy figure would equate to 333 kcal per hour.
But 100 Watts is only 86 kcal per hour!

The mismatch is so enormous that I feel I must have missed something.
I would be grateful to any physicist who can shed light on the figures.

The 50kCal is an estimate of the energy you burned (input) but the
power is the power you output.

A typical figure for efficiency of the body doing this type of work
is about 20%, which gives a large difference between the input and
output values.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On 17/03/2014 20:09, Chris wrote:
The gym has machines by pulsefitness.
There seems to be a mismatch in the numbers displayed.

After a bike session the summary was:
Power average: 74 Watts.
Time taken: 9 minutes.
Energy used: 50 kcal.

The above energy figure would equate to 333 kcal per hour.
But 100 Watts is only 86 kcal per hour!

The mismatch is so enormous that I feel I must have missed something.
I would be grateful to any physicist who can shed light on the figures.

The figures are fine, its just your body can't do a 100% efficient
conversion of stored chemical energy into mechanical power. So the
energy consumption by the body will be several times the plain
mechanical output (it will waste a good amount just producing heat for
example)


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Tue, 18 Mar 2014 03:23:50 +0000, John Rumm
wrote:

On 17/03/2014 20:09, Chris wrote:
The gym has machines by pulsefitness.
There seems to be a mismatch in the numbers displayed.

After a bike session the summary was:
Power average: 74 Watts.
Time taken: 9 minutes.
Energy used: 50 kcal.

The above energy figure would equate to 333 kcal per hour.
But 100 Watts is only 86 kcal per hour!

The mismatch is so enormous that I feel I must have missed something.
I would be grateful to any physicist who can shed light on the figures.

The figures are fine, its just your body can't do a 100% efficient
conversion of stored chemical energy into mechanical power. So the
energy consumption by the body will be several times the plain
mechanical output (it will waste a good amount just producing heat for
example)

I've seen the 'chemical to mechanical energy' efficiency for
biological systems quoted as being around the 50% mark but, of course,
there are additional 'parasitic' loads on top of whatever useful
muscular driven mechanical energy outputs are generated.

I'm guessing that this higher 50Kcal figure is simply derived from
the total watt hours from the generator by some sort of lookup table
based on actual test data collected from a representative sample of
volunteers employed in earlier studies of metabolic energy consumption
versus mechanical workloads. The manufacturer may simply have used
already published data to 'calibrate' their exercise bike.
--
Regards, J B Good

In article ], Chris ]
wrote:

The gym has machines by pulsefitness.
There seems to be a mismatch in the numbers displayed.... etc

First, if it's a gym machine then I'd be sceptical of its accuracy
anyway -- no disrespect to the gym owners, but public machines get a
hell of a lot of use (and abuse).

Secondly, see if Pulsefitness have a website (they do - I got that far
) and information about using the machine that you use. I sometimes
use a Wattbike at our gym, and Wattbike's website was very useful for me
in making more of the machine.

John

On 17/03/2014 23:07, The Natural Philosopher wrote:
You have missed the fact that ,mots people know how long 9 minutes is,
and roughly how much power a cyclist produces.

Apparently The Tour de France average is 400 watts.

No, I'm not that fit either!

Andy

In article ],
Another John writes:
In article ], Chris ]
wrote:

The gym has machines by pulsefitness.
There seems to be a mismatch in the numbers displayed.... etc

First, if it's a gym machine then I'd be sceptical of its accuracy
anyway -- no disrespect to the gym owners, but public machines get a
hell of a lot of use (and abuse).

I use a lot of different gym cycling machines when traveling, usually
in hotels where they are going to get less maintenance than in a gym,
and, somewhat to my surprise, they all pretty much agree on what
power output I generate at specific pulse rates. The only one that's
different is my one at home which under-registers power output, even
compared with my brother's identical one at his home.

I have not done a comparison on their conversion of energy output to
kCal burned, so I don't know if it's a simple 1:5 (or similar) ratio,
or if it takes into account loading, cadence, pulse rate (for those
that pick it up), etc.

I would also be interested to know the formula the Bremshey ones
use to report fitness. It's heavily based on the rate of drop of your
pulse rate for the 60 seconds after you finish exercising, but I don't
know if it takes into account any other metrics which it records
during the exercise.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On Monday, 17 March 2014 20:09:46 UTC, Chris wrote:
The gym has machines by pulsefitness.

An adult needs about 2000-2500 KCal a day - or very roughly 1-2 KCal per minute.

Even if you'd just sat next to the bike for 9 minutes, you'd have used (very roughly) 10-20 KCal, just staying alive and maintaining your body temperature.

IIRC vigorous exercise raises our heat output by about a factor of 2-3x compared to doing nothing.

So the overall figure of 50 KCal sounds reasonable - but remember that the *excess* calories used by exercise is somewhat less than that.