Class Notes (1,100,000)
CA (630,000)
UTSG (50,000)
BCH210H1 (500)

lec32 Soon-yi part 5 fat mobilization

Course Code
Michael Baker

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Case Study: Soon-yi Part IV: Beijing 2008 – At the Olympics at the 32 km
1. Glucagon and Adrenaline Effects: Liver and Muscle
2. Fat Mobilization
3. Fatty Acid Activation and the Carnitine Shuttle
4. Steps in Fatty Acid β-Oxidization
5. Fat and Glycogen as Fuels throughout the Race
Soon-yi Part 6: Beijing 2008 – Representing Canada
- Soon-yi made it onto the Canadian Olympic Team and she is currently at the
32 km marker of the marathon!
- The race began 2h ago at 5pm from Tian’anmen Square and Soon-yi is
maintaining a steady 270m/min
- She built up her glycogen reserves to 230 g before the race
oNeeds glycogen so she can access fat
oCan use fat efficiently
Need to blend fuels on a long distance race, cannot run on just
- Soon-yi ate a simple carbohydrate rich meal 3h before the race, but no food
- She took a small coffee 1h before the race as coffee extends her endurance
- She is consuming small amounts of water along the route
- At the race start Soon-yi weighed 42kg
- At the 32 km mark she has used up 1000 kcal of energy:
o175 g of glycogen and 33 g of fat
Blending fuels
Trying to increase fat use and decrease glycogen use so that
glycogen lasts until the end
Fat burns best in flame of carbohydrates
oBurn off fat most efficiently as long as you sustain
carbohydrates also burning alongside
- Carbohydrate gives 4 kcal energy/g and fat gives 9 kcal energy/g
oThus fat is a better fuel but must be mobilized from fat cells in fat
- Strategic use of fuels in a long race is very important
oFor the first half of the marathon Soon-yi derived >80% of her energy
from glycogen
Main fuel is glycogen for first half of race
oBut now at 32km she is using a blend of 60% glycogen and 40% fat for
Shifting to use of fat
Fat provides a lot of energy
- It is imperative that she keep increasing the use of fat and not run out of
glycogen in this last 10 km of the race
oWhen glycogen reserves are gone, runners suffer both a remarkable
loss in running efficiency and drop in speed called “hitting the wall”
Efficiency goes right down, hitting a wall
Cannot make efficient use of fat without glycogen
- Soon-yi is running well and is within a group of the fastest 6 runners

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- But she is suffering in the heat!
oShe has lost almost 1L of body water (and drunken about 300 mL) and
her body temperature is up to 39°C

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What are Soon-yi’s metabolic fuel responses at 32km?
- While glycogen is easily mobilized, fat takes time
oGlycogen is right there in muscles, readily broken down
Like a fridge
oFat is harder to access
Like a store, gotta go get it!
In fat tissue (not in same cell), have to go down and get it to
Takes a bit of time to energize
Have to get it mobilized, but it only does so when you
have been exercising after a significant amount of time
oSoon-yi used little fat until she got near the 10km marker of the
- Her blood insulin levels are low:
oMaintained, but not rising since not eating
oAdrenaline and glucagon dominate her fuel responses
- Liver continues to mobilize glycogen to support blood glucose levels
oGlycogen will go to glucose-6-P through glycogen phosphorylase
oGlucose-6-P broken down by glucose-6-phosphatase to deliver glucose
out to blood, to sustain blood sugar levels
Liver is making sacrifice; not using any more sugar since it
knows it is needed
“Gotta use glycogen to sustain blood sugar, have to slow
down glycolysis”
oLiver, in response to adrenaline and glucagon, has elevated PKA
Shutting down glycolysis – cannot deplete source of glucose
Source that is going to keep blood sugar okay to keep
brain going
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