Ergo-meter power and calorie calculations.

hi,

i've got old exercise bike (ergometer) i'm trying build new interface for. bike old precor c846, works ok, displays single metric @ time i.e. pedal speed, or power or distance or time or calories.

my interface pretty simple, has 2x20 lcd display can show data @ same time. haven't hacked old bike, i've added own hall probe flywheel (to pick pedal speed) , added button allow me set resistance level match of bike. power calculated map() function replicate shown on ergometer.

my problem can metrics match of exercise bike except calories consumed. if set bike 'rpm' figure matches unit gives, if set bike 'power', figure matches unit, , same time, distance , heartrate.

the difference comes working out total calories consumed in exercise session.

i can work out energy used (joules) following...

code: [select]

  // work out joules used far. joule work required produce 1 watt 1 second.
  if ((millis() - ts5) >= millisbtwnjoule)
  {
      // power integer (typically 220 watts), joule long , millisbtwnjoule integer
      joule = joule + long((long)((long)power*(long)millisbtwnjoule)/1000l);
      //serial.print("power=<");serial.print(power);serial.print(">, joule=<");serial.print(joule);serial.println(">");
    ts5 = millis();                   // timestamp moment joules used calculated.
  }

the figure joules seems expect. 1 watt 1 joule per second, if pedal @ 200watts 10 seconds use 2000 joules.

there's simple conversion factor calories....

code: [select]

const float cf4 = 0.000239006;                   // conversion factor converting joules calories (1 joule = 0.000239006 kilocalories)

      // base unit's i'm sticking si units power & energy (i.e. watts , joules), display
      // purposes use calories instead comparison exercise bike
      calories = (int)((float)joule*(float)cf4);
      //serial.print("calories=<");serial.print(calories);serial.println(">");

the problem can't figure calories match shown on exercise bike. can exact match pedal speed , power, exercise bike shows me using 4 times many calories unit calculates. @ point i'm not asking code fix, i'm asking sanity check on understanding of energy , power , relationship between them. principle of i'm doing right?

the calorie figures exercise bike displays seem approximately match see on other bikes when similar training session @ gym, don't think there's problem it. know power matches power bike shows, , relationship between power , calories should simple can't figure can have gone wrong.

quote from: fulliautomatix on nov 03, 2015, 09:40 am

the figure joules seems expect. 1 watt 1 joule per second, if pedal @ 200watts 10 seconds use 2000 joules.

that's mechanical output power/work.

quote from: fulliautomatix on nov 03, 2015, 09:40 am

there's simple conversion factor calories....

and 'calories' measuring 'input' driver eats meals.

don't forget "efficiency"!

same thing combustion engine. there more energy in fuel mechanical energy crank shaft. rest dissipated heat , not delivered mechanical work.

the human muscles not provide 100% efficiency, not calories eaten become mechanical joules on pedal.

efficiency of human muscles 20% 25%.

so each 4 or 5 calories (joules) eaten food can becom 1 calorie (joule) mechanical output power @ pedal.

so not need factor convert units joules calories, need factor take consideration efficiency of human body while creating mechanical power food calories.

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