# kj use - just checking

#### grahamspringett

##### New Member
If I'm home from a ride and my PowerTap says I used 1800kj of energy, I need to multiply that by 4 or 5 to work out how much energy I put out thanks to the body's inefficiency.

So, if I'm on a ride and I have used 500kj for the first hour, I need to take in 2000-2500 to replace that energy, don't I?

I'm looking at gels n drinks n stuff and working out if I need to use both on big rides and races.

grahamspringett said:
If I'm home from a ride and my PowerTap says I used 1800kj of energy, I need to multiply that by 4 or 5 to work out how much energy I put out thanks to the body's inefficiency.

So, if I'm on a ride and I have used 500kj for the first hour, I need to take in 2000-2500 to replace that energy, don't I?

I'm looking at gels n drinks n stuff and working out if I need to use both on big rides and races.
Yes, but 2000-2500 KJ are, more or less, 500 KCal so you don't really have to convert or doing calculations. Just read KJs as they were KCal !

Simone@Italy said:
Yes, but 2000-2500 KJ are, more or less, 500 KCal so you don't really have to convert or doing calculations. Just read KJs as they were KCal !

But if I have a gel which has around 300-400kj, that's the same units as my PT tells me. So I'd need six gels.

grahamspringett said:
But if I have a gel which has around 300-400kj, that's the same units as my PT tells me. So I'd need six gels.
oh, yes. It depends: in Italy we have KCal on the foods' labels, if you have KJ then your calculation were correct.

grahamspringett said:
If I'm home from a ride and my PowerTap says I used 1800kj of energy, I need to multiply that by 4 or 5 to work out how much energy I put out thanks to the body's inefficiency.

So, if I'm on a ride and I have used 500kj for the first hour, I need to take in 2000-2500 to replace that energy, don't I?

I'm looking at gels n drinks n stuff and working out if I need to use both on big rides and races.

The only error in this logic is assuming that you should replace 100% of the energy that you are expending during exercise iteslf. That might be be normal during a very long, very low intensity ride, or necessary during something like the Race Across America (RAAM), but otherwise you will always be relying more on endogenous energy sources (e.g., muscle glycogen) than exogenous energy sources (e.g., a gel or sports drink) during exercise.

acoggan said:
The only error in this logic is assuming that you should replace 100% of the energy that you are expending during exercise iteslf. That might be be normal during a very long, very low intensity ride, or necessary during something like the Race Across America (RAAM), but otherwise you will always be relying more on endogenous energy sources (e.g., muscle glycogen) than exogenous energy sources (e.g., a gel or sports drink) during exercise.

How about during a road race where say 2000kj go out the window. How many kj, or what percentage of kj indicated on my PT, would I need to replace so I don't suffer a drop in performance?

grahamspringett said:
How about during a road race where say 2000kj go out the window. How many kj, or what percentage of kj indicated on my PT, would I need to replace so I don't suffer a drop in performance?
Everybody is different, I think. I know that I start cramping around 1800 kJ if I don't get enough calories in the hours before the race and during it.

grahamspringett said:
How about during a road race where say 2000kj go out the window. How many kj, or what percentage of kj indicated on my PT, would I need to replace so I don't suffer a drop in performance?
I think what he's saying is that it depends on how many kJ you have stored in your muscles. That's where carboloading comes in, so you DON'T have to replace every kJ you burn during a race.

If TSS represents total glycogen used during an exercise then IF^2 should be relative amount of consumption. Based on this and total Kj is it possible to estimate the amount of consumed glycogen?

For some reason, the number ~800 kJ sounds familiar for the amount stored locally in the muscle tissue as glycogen, and additional is being metabolized remotely during the time when those stores are being used.

frost said:
If TSS represents total glycogen used during an exercise then IF^2 should be relative amount of consumption. Based on this and total Kj is it possible to estimate the amount of consumed glycogen?
It's an interesting thought but I'm not sure if the scaling used in the Normalised Power algorithm (designed to take into account the non-linear nature of physiological responses to intensity) is sufficiently robust to draw the conclusion that TSS ~= kJ(glycogen) x scaling factor, with the scaling factor presumably related to FTP, since of course TSS is relative to FTP and there must be an absolute and relative component if using TSS in this way.

I'm also not so sure it actually matters. Say you do a hard and variable intensity 6+hr effort (e.g. a Tour Stage), can your injestion keep up with such potential calorie intake levels anyway? IOW, you injest as much as you can cope with rather than what might be suggested by such an assessment.

Alex Simmons said:
I'm also not so sure it actually matters. Say you do a hard and variable intensity 6+hr effort (e.g. a Tour Stage), can your injestion keep up with such potential calorie intake levels anyway? IOW, you injest as much as you can cope with rather than what might be suggested by such an assessment.
Yep, just after writing the question I was realized that it's probably just mixing abstract concepts with something they do not have anything to do with and even if they did what is the practical application. But making some discussion anyway
.

frenchyge said:
For some reason, the number ~800 kJ sounds familiar for the amount stored locally in the muscle tissue as glycogen, and additional is being metabolized remotely during the time when those stores are being used.
I seem to remember it being around 1800 kJ but that could be the sum of the two parts that you mentioned or I might just be remembering incorrectly.

The 1800 figure first caught my attention because that was about the point where I was having cramping problems on any particular day so that made the theory of glycogen depletion causing cramping more plausible to me.

Steve_B said:
I seem to remember it being around 1800 kJ but that could be the sum of the two parts that you mentioned or I might just be remembering incorrectly.

The 1800 figure first caught my attention because that was about the point where I was having cramping problems on any particular day so that made the theory of glycogen depletion causing cramping more plausible to me.
Higher than that.
About 2000kCal according to my ex phys textbook (although you may have been referring to the kJ output as opposed to our glycogen stores)
And FFA stores are about 10^5 kCal

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