Questions that my teachers hated me for!

Here's my question of the moment, I swear its not a logic problem just looking for a right answer, or at least opinions.

Say you bike for four hours at high intensity so that your output is gradually declining. Your successive journal entries look like this:

1 hr @ 20 MPH

1 hr @ 19 MPH

1 hr @ 18 MPH

1 hr @ 17 MPH

Logic says the fourth hour consumed the least energy as you only moved the mass 17 miles (less than the other three hours). But is this accurate? If your muscles are fatigued and actually working hardest in that last hour would they consume MORE energy?

Thanks in advance for any input.

Kevin

I believe this is where the whole "efficiency" comes in. Lets say with fresh muscles you went for 1hr @ 20 and did 600Kj of work. Assuming your muscles were super efficient that translates to ~600Cal burned to do that work. Now the last hour you only did 500kj of work, but legs were tired, you weren't as efficient at pedaling, rocking etc, so you burned somewhat more Calories to do those 500Kj of work. Well at least that is how I see it.

UD

I would think that the "law" of diminishing returns would set in.  Did the muscles during the last hour consume less energy because there was less energy available to consume?

Original Post by pilgrimdude:

I would think that the "law" of diminishing returns would set in.  Did the muscles during the last hour consume less energy because there was less energy available to consume?

Well that is somewhat of a different issue of nutrition while on a bike. It can account for decreased output, but not really the amount of calories burned.

UD

Interesting question. I don't know the answer.

However, in the thread, note that kJ and kcal (or Cal) are not equivalent - kJ = about 4.2 x kcal/Cal.

In my opinion your assumption that your muscles were working hardest in the last hour is erroneous.  Fatigue has set in and glycogen is being depleted and the muscles are no longer able to work as hard as they were in the earlier part of the ride, this is why the average speed is dropping, cals. per min. are dropping also. 

Also, ifthe rider is outdoors riding over the road, changing conditions will affect speed.  In other words, the rider could be generating the same power and and burning the same calories per minute for the entire ride but was riding with the wind for the first half of the ride and is riding against the wind on the return or perhaps the fist part was down hill, etc.  Outdoors the variables are changing constantly.

Original Post by foiegras:

Interesting question. I don't know the answer.

However, in the thread, note that kJ and kcal (or Cal) are not equivalent - kJ = about 4.2 x kcal/Cal.

Actually other way arround 1 kC = 4.18 kJ. That is why I was talking about the efficiency. With a fit rider, fresh muscles, good pedaling technique efficiency is at it's best, but still pretty poor. So it takes about ~4kC to produce 1kJ, thus for all intent and purposes ratio of kC to kJ is 1 to 1. When fatigue settles in, pedaling technique not as good efficiency gets even worse so now the ratio could be 1.2 to 1.

UD

I can tell you from watching my power meter that, at the beginning of a long, hard ride, when I'm feeling fresh, I can be laying down 200 Watts and it feels like the bicycle has no chain, but at the end, when I'm wrung out and I'm just trying to get home, and it feels like I'm working hard, I might only be putting down 120-140 Watts.  Perceived effort can be a real liar, but Watts don't lie.

Yep, they don't. he he.

UD

umneydurak, it is not "the other way around."

I wrote: "kJ = about 4.2 x kcal/Cal"

An example - how many kJ is 1000 kcal?

1000 kcal/Cal x 4.2 = 4200 kJ

Clear now?