Let's say you've been running for 60 minutes and assume you've depleted the glycogen in your muscles. Does your body then take fat cells throughout your body and turn them DIRECTLY into glucose/glycogen for your cells to use? Or does your body take the fat cells and use them for some other process that is then use to produce more glucose/glycogen? Thanks in advance.
no... you body recycles lactate from your muscles and catabolized proteins to make more glucose.
beta-oxidation of fats will also provide energy, but this cannot be used to make glucose
So then I don't understand how you ever 'burn' any fat...Why do people say you need to run for atleast 30 min to burn any fat?
I know a calorie defecit is required...but I don't get how this works...When does your body use fat for energy and how does it do so? It doesn't just become energy it becomes something else first doesn't it? What would that be?
Last edited by Deathwish; 10-09-2005 at 01:11 PM.
That "thirty minute" thing is really overstated. Basically, the idea is that you need to run through your available glucose/glycogen before you "switch tanks" to the fat stores. In practice, you burn both throughout (at least, as I understand it). You're still creating a caloric deficit, even if you don't go that long.
One of the many, many reasons to never do cardio before you lift, by the way. Might as well put your glycogen and glucose to good use wrecking muscle tissue. Do the cardio at the end.
:withstupiOne of the many, many reasons to never do cardio before you lift, by the way. Might as well put your glycogen and glucose to good use wrecking muscle tissue. Do the cardio at the end.
"The only easy day was yesterday."
Yes you need to use your current glucose stores first before the body starts to degrade adipose tissue to release lipids (fats.)Originally Posted by Deathwish
Your fat is a store and therefore if you cut out eating completely your body attempts to *keep* fat and will degrade other tissues first - including protein and muscle.
As for how fat becomes energy.. it's a long and complicated series of metabolic pathways and knowing them won't really help your dieting efforts. If you really want to know then consult a biochemistry text book or look it up on google.
Your muscles dont directly use glucose either.. glucose undergoes glycolysis and becomes pyruvate, then undergoes 2 more series of reactions to become ATP (adenosine tri-phosphate) which is used as energy when ATP => ADP + P.
Losing a P (phosphate) causes a release of energy which can be used to move a muscle fibre etc.
By the way your muscles dont utilise glycogen either. Glycogen needs to be degraded and converted into glucose before it undergoes the steps above.
You are on the way.Originally Posted by Davidelmo
Only plants have the neccessary enzymes to turn fat into sugar/glucose. It is called the glyoxalate cycle. In animals fat is converted to "ketone-bodies".
Animals can make sugar/glucose from protien (glucneogenisis). That is why it is not good to lose weight through dieting.Better to manipulate your endocrine system, also an efficient way to increase muscle.
Been a while since I studied this crap, so it might be a bit rough around the edges.
Did you also know that muscles do not need energy to contract? I kid you not. I'm not going to go through the whole crossbridge cycle, but have a think about rigormortis and the cramps you get when you exercise.
That's preposterous.Originally Posted by Surferboy
Rigor mortis is caused by a 'locking' effect caused by lack of free ATP, not a 'contracting' effect. Anything which moves requires energy.
Going back to school will help you on that one.Did you also know that muscles do not need energy to contract?
"The only easy day was yesterday."
the intensity of the exercise determines the energy system used...Originally Posted by Built
Yep, lol.. I studied this crap last year (med student) but I was just doing that from memory. It's appalling how much I've forgotten really!!Originally Posted by Surferboy
This is simply wrong. Lipid use as an energy substrate is primarily dependant on INTENSITY. Think to the BS of the 'fat burning zone'. Technically, at rest you burn the most fat as it's near 100% lipid use. You would need to exercise for hours to burn through glycolytic pathways.Originally Posted by Davidelmo
When a marathon runner 'hits the wall', his glycolytic pathways are reaching exhaustion. No one does that running on a treadmill unless they're in ketosis.
Here's some data from a VO2 test I recently performed on a young lady. An RER of .70 would denote 100% fat use, and 1.0 or greater is 100% carbohydrate. As you can see, at the beginning stages fat use is greater than at the latter stages, as intensity increases (you can see intensity increasing by looking at VO2)
TIME-- VO2-- RER
1.0185 - 9.223 -0.854446
2.0216 -17.990 -0.709531
3.0171 -25.009 -0.818778
4.0095 -33.826 -0.891522
5.0015 -35.733 -0.964493
6.0196 -37.903 -0.99148
7.0165 -39.991 -0.98607
8.0076 -41.856 -1.013505
9.0136 -44.141 -1.030927
10.013 -46.717 -1.05455
11.008 -48.127 -1.088356
12.007 -50.539 -1.108845
12.365 -50.651 -1.145526
Last edited by Glaim; 11-04-2005 at 12:09 AM.
Bench - 305
Deadlift - 495
Squat - 385