Download IV. Energy Requirements of Skeletal Muscles

Energy Requirements of Skeletal
Muscles
Metabolism of skeletal muscle depends on O2 uptake
-- depends on whether exercise is light,
moderate, heavy, which depends on a
person’s maximum capacity for aerobic
exercise
--Maximal oxygen uptake (aerobic
capacity), abbreviated VO2 max
It is expressed as ml O2/min/kg of body
weight
High = 84 ml/min/kg (young male
athlete)
Low = 12 ml/min/kg (older, sedentary
people)
Capacities for Aerobic Oxygen
From the Internet
Muscle Fuel Consumption During Exercise
Light – (and resting muscles)
get most of their energy from
fatty acids
Moderate (just below the
lactate threshold) energy is
obtained about equally from
fatty acids and glucose
Heavy – glucose, (from the
muscle’s stored glycogen and
from blood plasma)
becomes increasingly
important
LEG Muscle GLUCOSE Consumption During Exercise
GLUCOSE UPTAKE: Exercise
stimulates glut 4 transporters to be
inserted into the plasma membrane
of muscle cells. The more intense
the exercise, the more glut4
transporters are inserted.
-- this is independent of insulin
CYCLE ERGOMETER
Oxygen Debt: the length of time it takes to ‘catch your
breath’ after lactic acid build-up
Oxygen debt is the
amount of oxygen
that you owe yourself
to convert lactate
back into pyruvate
and restore aerobic
respiration.
• Click here for a 1 minute video
Production of Phosphocreatine
Rapid production of ATP is accomplished by combining ADP with
inorganic phosphate derived from phosphocreatine
Phosphocreatine is a high-energy reserve found in muscle cells.
The reverse reaction is catalyzed during rest (to restore depleted supplies.
Different Exercise Regimens
between twins
This is a famous photograph showing
differences in body types between
identical twins that simply used
different exercise regimens.
Skinny guy – a runner, high aerobic capacity
and endurance
Buffed guy – a weight lifter, does his exercise
with short bursts of energy, rather than
endurance.
What’s going on here?
SLOW- AND FAST-TWITCH FIBERS
SLOW-TWITCH:
Contract slowly
often “postural”
high oxidative capacity
contract without fatigue
numerous mitochondria
myoglobin
sometimes called red fibers
FAST-TWITCH:
Contract quickly
less capillary supply
fewer mitochondria
adapted to metabolize
anaerobically
use a glycogen storage
examples: soleus
(leg)
examples:
extraocular muscles that
position the eyes
Relative Abundance of Fiber Types
Muscle fatigue
• Defined as a reversible,
exercise-induced
reduction in the ability of
a muscle to generate
force
• Many causes, which
seem to be determined
by the type of exercise.
• E.g. lifting an extremely
heavy weight. K+ builds
up outside of muscle
cells
Adaptation to Endurance Exercise Training
Student activity:
Compare the storage
of fatty acids in obese
people with the storage
of fatty acids in athletes.
What’s the difference?