I imagine the guys who turned a slip of the typing finger into a major
flamewar are all fat and diseased from sitting at their keyboards all
day long waiting to catch someone's fart so they can light it to start
a flamewar. Here, with thanks to those who offered amendation, is the
corrected version in which, as Ian Bell has pointed out, 1kW is still
860kcal, so that the conclusion I intended is changed not one jot or
tittle:

Every time I come back from riding my bike, the bike computer tells me,
among other useful information like my pulse rate, how high the hills
were, how fast I pedalled, what my road speed was, the temperature,
rates of descent, etc, etc, etc, much more stuff which I have my
computer print out in neat graphs. Among all this the bike computer
tells me how many watts I expended. The thing cheats of course, as it
takes a downhill or level-road ride as zero watts (you're still
expending energy). It gives peak output and an average for the ride. So
the energy expended is the length of the ride (it only ticks the clock
when the wheels are moving) multiplied by the average output. But get
this, one kilowatt-hour is 860kcal. So, if you've gone for a ride that
will burst your average audiophile (middle-aged, overweight, fatarsed,
except for Patrick and me, who are ex-athletes and cyclists still) out
into heavy perspiration, say 100W average for an hour, which allows for
some extended peaks at 250W which will drive your heartbeat up to the
maximum, which does no one any good, the energy expended is 0.1kW or
86kcal. In other words, an hour's hard ride burns only 86 nutritional
calories. You see, those calories on food packets are really
kilocalories aka "nutritional calories". You guys better stop eating
altogether or you'll have to be on your bikes eight hours a day.

Obligatory on-topic comment: Turning every thousand calories into a
"calory" without warning is a worse scam than rating audio gear in "RMS
watts" or "music watts".

ADDENDUM: Exercise energy expenditure is measured as the additional
energy burned over the maintenance energy at rest of about 100W per
hour.

Andre Jute
The trouble with most people is not what they don't know, but what they
know for certain that isn't true. ---Mark Twain