Download ATP attachment breaks the cross bridge (actin/myosin)

The Muscular System –
Muscle Metabolism
Muscle Metabolism
• Metabolism is the breakdown of food for cellular use
• Muscle metabolism is the breakdown of glucose for energy
• ATP is the source of energy for muscle contraction
 ATP attachment breaks the cross bridge (actin/myosin)
 ATP to ADP extends myosin head to working position
•
Muscles store a very limited amount of ATP (4-6 seconds worth at
most).
•
ATP must be regenerated if contraction is to continue beyond
4-6 seconds.
•
ATP can be generated by one of three pathways….
Aerobic Muscle Metabolism
• Occurs in mitochondria and requires
oxygen
• Glucose + oxygen carbon dioxide +
water+ energy (~36 ATP)
• Requires enough available oxygen
relative to ATP demand
• Prolonged activities which maintain
relatively constant heart rate
• Posture, most daily movements, easy
exercise
Anaerobic Metabolism– Glycolysis
 Surface of mitochondria and does
not use oxygen.
 Glucose lactic acid +energy
(~2 ATP)
 Lactic acid interferes with muscle
contraction (‘muscle fatigue’)
 ATP demand exceeds available O2
 30-40 seconds before muscle
fatigue occurs
 Tennis, soccer, 100 meter swim
Anaerobic Metabolism– Creatine
 Creatine phosphate
stored in muscle used to
make ATP from ADP
 Creatine phosphate +
ADP
ATP (1 ATP)
 Quick source of ATP,
when exercise starts
 Enough creatine for 1015 seconds of
contraction
 Weight lifting; 100 M
dash
Muscle Metabolism
Summary
Creatine Pathway
Glycolysis Pathway
Aerobic Pathway
no
no
yes
Amount of ATP
1 ATP
2 ATP
36 ATP
Duration
15 sec
30-60 sec
hours
creatine
lactic acid
CO2, H2O
Requires Oxygen
By-product
Advantages
•rapid energy
•easily mobilized
•quick energy
•does not require
oxygen
•moreATP/glucose
•waste products
are easy to excrete
Disadvantages
•small amount of
creatine available
•small amount of
ATP
•lessATP/glucose
•lactic acid produces
muscle fatigue
•slower
•limited by oxygen
Muscle Metabolism
Fast Twitch/Slow Twitch Muscle
Muscle Metabolism
Fast Twitch/Slow Twitch Muscle
Fast Twitch
Slow Twitch
Lack myoglobin and are lighter in
color
Contains myoglobin and are dark
in color
Contain few mitochondria
Contain many mitochondria
Primarily anaerobic – does not
need O2 and produces lactic acid
Primarily aerobic – uses O2 and
produces CO2 and H20
Fatigue easily
Fatigue slowly
Produce more forceful contraction
Produce less forceful contraction
Increase in size with training
Do not increase in size
Muscle Fatigue
 Muscle loses ability to contract
 Occurs when ATP production fails to
keep up with ATP use.
 Relative deficit of ATP, not
absence of ATP producing a
continuous state of
contraction (rigor mortis)
 Accumulation of lactic acid and ionic
imbalances also contribute.
 decreases muscle pH
 causes burning sensation
 interferes with actin/myosin
binding