8- Question 4 - Energy burned in uphill biking - by Kambiz Ehsani - 4/22/2018 - Solved

You are biking uphill with a constant speed of 15 miles per hour. The weight of the bike and you together will be 200 pounds.Assume the slope 5%. How many Kilo Calories will you pedal in 10 minutes? is that the same as Kilo Calories burned by your body? please explain all of your assumptions:

The question was designed by myself as one day I thought, how the apps on my smart phone calculate my Kilo Calories burned :-)

Solution:
Writing the free body diagram of the mass of you and bike as a rigid body on the inclined surface:
f = Friction force = m*g* Sin (Teta)
Power of pedaling = m*g* Sin (Teta) * v = hp = horse power
v = assumed constant velocity
Teta = the angle for the slope
hp = 200 * 5/(10025)^0.5* 15 * 0.44704/0.3048 = 0.4 = 294 watts = 70 cal/sec
Pedaling Power = Pp = 70 cal / sec = in 10 minutes or 600 seconds = 42,000 cal = 42 kcal

This is the pedaling Kilo Calories. The body has an efficiency in converting the food intake energy to exercise energy or useful work. This efficiency is different from person to person. for every 1 Calorie we eat only 0.75 calories turns into useful work. So the efficiency of the body is approximately 25%. So the pedaling calorie and burning calories are not the same. So the burning calories are:

Burned Power = Pb = Pp / 0.75 = 56 Kcal


By the way all the units on the Fitness machines should be expressed as Kcal and it is as we know expressed as Cal.