energy use

werzel said:

just wondering if any of you out there with calorie counting hrm's have noticed how much energy you are chewing up when pushing fairly hard. what sort of numbers do you get?

I have only recently started using an HRM with a calorie counter so I find your question very interesting. Yesterday I rode about 2 hours and 15 minutes and today about 1 hour and 15 minutes, both rides at an average of about 78 - 79% of MaxHR and according to my HRM in both cases I burned very roughly 1,000 calories per hour (I didn't write the numbers down so I can't remember the exact details ). The rides included hills and I am about 82kg. My HRM is a Sigma Sport PC14 and I set the "specific sport factor" at 00069.

as little as 700 per hour and as much as 1200 per hour, depending upon intensity.

Mansmind said:

as little as 700 per hour and as much as 1200 per hour, depending upon intensity.

i would second that, i have burned never seen less than 700 even on a recovery ride, whilst have once slightly exceeded 1200 in a 25 mile time trial.

surely there is NO better sport for burning calories?! I know running burn a few more per hour, but show me a runner who can do 4 hours a day!

from what i can gather, i thought it would be around those sort of figures. wonder if there is a direct correlation between power output and energy use?

werzel said:

from what i can gather, i thought it would be around those sort of figures. wonder if there is a direct correlation between power output and energy use?

for any specific rider yes, but even then...as you get more fit you'll burn less energy to generate the same power.

do you think you burn less energy for same power output or get better at accessing energy stores and therefore burn more energy resulting in higher sustainable power output?

werzel said:

do you think you burn less energy for same power output or get better at accessing energy stores and therefore burn more energy resulting in higher sustainable power output?

actually, from what I've read and understand, both would happen to a certain extent.

As an example, you get fitter and are able to ride at a higher effort = higher power. (longer)

Also as an example (if you're like me). When I first started riding, generating 200 watts took considerable effort (higher PE and HR). Now, generating 200 watts seems relatively easy (lower PE and HR). I'm not expending as much energy to generate the same power.

werzel said:

from what i can gather, i thought it would be around those sort of figures. wonder if there is a direct correlation between power output and energy use?

The relationship between energy expenditure and power output is

Energy expended = power (/1000) * time (secs)

For e.g., if you ride at 200 W for one hour, the mechanical energy expended is = 0.2 * 3600 = 720 kj

To convert kj to Kcal divide by 4.18 = ~ 172 Kcal.

However, the human body is ~ 20 - 25 % efficient when cycling, so that 172 Kcal becomes an energy expenditure of ~ 689 Kcal to ~ 861 Kcal energy expended.

Your efficiency can be calculated in a physiology lab by measuring expired respiratory gases. However, the efficiency you record will vary vary under different conditions and cadences. It will also increase as you ride at a higher power and decrease at lower power. Therefore, the best measure (in the real world) of actual energy expenditure is a ball-park estimate of expenditure by looking at how many kj you expend (on a power meter) and just changing the units directly to Kcal (i.e., in the above example, best measure is to say you expended 720 Kcal).

A HRmonitor can't accurately measure energy expenditure.

Out of interest, the lowest i've seen when *racing* is one of the riders in TdF expending ~ 350 kj/hr. During training i've seen less!

Ric