BBS2041 Lectures Iris Donker
Lecture – Exercise physiology and
substrate metabolism
Basics on exercise physiology and substrate metabolism
Exercise physiology – the biological processes and adaptive response to exercise (both acute and
long-term adaptation).
Skeletal muscle
Why is skeletal muscle tissue so important?
• Main factor in mobility / physical performance
• 50% of body weight
• Major metabolic organ
• Major factor in health
• Highly adaptive tissue
Muscle fibers
One muscle fiber is the same thing as a muscle cell. A
muscle cell is a multinucleated cell.
2 types:
• Type I: endurance
• Type II: strength → 2 types: Type IIA and type IIB (also called type IIX)
Humans always have mixed muscle fiber types within all muscles. It’s somewhere around 50/50, but
you can change this a little bit with training.
1
,BBS2041 Lectures Iris Donker
The effect on exercise intensity on the percentage of active muscle fiber type
During endurance training: At first type I fibers
will be recruited. At about 40-50% of VO2max the
type IIa fibers will also come into play. Only at the
very end, when the intensity comes close to the
maximum, that’s when type IIx fibers are used.
During resistance training: The scale is different.
At about 20% of VO2max you already start
recruiting type IIa fibers. And around 40-50% you
already start recruiting type IIX fibers.
Type of activity vs energy systems
Different energy transfer systems:
• First few seconds → Free ATP & Phosphocreatine (PCr)
o really high intensity, really short duration:
• 1 to 1.5 minutes → Glycolysis
o For which you need carbohydrates
• After 1.5 minutes → everything is oxidative metabolism
o For which you need carbohydrates and fat
Free ATP and PCr
Glycolysis
During glycolysis carbohydrates are converted into pyruvates. In this process only 2 ATP are
generated. Afterwards these pyruvates can be converted into acetyl-CoA.
Oxidative metabolism
Fat is broken down and the fatty acids go into beta-oxidation where also acetyl-CoA is the end
product. The acetyl-CoAs of both pathways (glycolysis and beta-oxidation) can then be used in
oxidative metabolism
2
, BBS2041 Lectures Iris Donker
3
Lecture – Exercise physiology and
substrate metabolism
Basics on exercise physiology and substrate metabolism
Exercise physiology – the biological processes and adaptive response to exercise (both acute and
long-term adaptation).
Skeletal muscle
Why is skeletal muscle tissue so important?
• Main factor in mobility / physical performance
• 50% of body weight
• Major metabolic organ
• Major factor in health
• Highly adaptive tissue
Muscle fibers
One muscle fiber is the same thing as a muscle cell. A
muscle cell is a multinucleated cell.
2 types:
• Type I: endurance
• Type II: strength → 2 types: Type IIA and type IIB (also called type IIX)
Humans always have mixed muscle fiber types within all muscles. It’s somewhere around 50/50, but
you can change this a little bit with training.
1
,BBS2041 Lectures Iris Donker
The effect on exercise intensity on the percentage of active muscle fiber type
During endurance training: At first type I fibers
will be recruited. At about 40-50% of VO2max the
type IIa fibers will also come into play. Only at the
very end, when the intensity comes close to the
maximum, that’s when type IIx fibers are used.
During resistance training: The scale is different.
At about 20% of VO2max you already start
recruiting type IIa fibers. And around 40-50% you
already start recruiting type IIX fibers.
Type of activity vs energy systems
Different energy transfer systems:
• First few seconds → Free ATP & Phosphocreatine (PCr)
o really high intensity, really short duration:
• 1 to 1.5 minutes → Glycolysis
o For which you need carbohydrates
• After 1.5 minutes → everything is oxidative metabolism
o For which you need carbohydrates and fat
Free ATP and PCr
Glycolysis
During glycolysis carbohydrates are converted into pyruvates. In this process only 2 ATP are
generated. Afterwards these pyruvates can be converted into acetyl-CoA.
Oxidative metabolism
Fat is broken down and the fatty acids go into beta-oxidation where also acetyl-CoA is the end
product. The acetyl-CoAs of both pathways (glycolysis and beta-oxidation) can then be used in
oxidative metabolism
2
, BBS2041 Lectures Iris Donker
3
