Cardiorespiratory System 1
Case Study Essay Question: Cardiorespiratory System
Morrow L. Berberich
Department of Allied Health Professions, Liberty University
EXSC 510: Advanced Exercise Physiology
Dr. Andrew Bosak
November 6, 2022
Morrow Berberich
Cardiorespiratory System 1
Energy comes in many interchangeable forms such as mechanical, electrical, and
chemical, which results from food sources, chemical reactions, and metabolic processes.
Carbohydrates and fats are the main sources of energy during exercise, while protein provides
minimal energy (Blake et al., 2019). The body uses protein to build and repair tissues, muscles,
and cells. Protein can be used as a source of energy by breaking down muscle tissue into amino
acids and converted into glucose to synthesize glycogen. This process occurs when there are not
enough carbohydrates to produce glycogen and its stores are depleted.
During exercise, muscular contraction uses adenosine triphosphate (ATP) to produce
instantaneous energy. ATP development requires energy and the merging of adenosine
diphosphate (ADP) and inorganic phosphate. Adenosine triphosphate can then be used for
muscular contractions, metabolic energy processes, or stored in muscle cells (Powers & Howley,
2018). The body uses three metabolic pathways to make ATP which are the phosphagen,
glycolytic, and oxidative systems. Oxygen availability is not involved in phosphocreatine
hydrolysis and anaerobic reactions to produce energy. However, aerobic pathways like oxidative
phosphorylation rely on oxygen to complete reactions.
The phosphagen (ATP-PC) system provides energy for rapid bursts of high-intensity
exercise lasting up to 10 seconds, which includes sprinting, weightlifting, and shot put. The
reaction of phosphocreatine and ADP are catalyzed by the enzyme creatine kinase to produce
ATP and creatine (Powers & Howley, 2018). At the start of exercise, ATP is quickly broken down
into ADP and organic phosphate. A 100m sprinter that finishes a 100m race in 10 seconds will
predominately use the phosphocreatine energy system. There is a limited amount of stored
creatine phosphate and ATP in the body’s muscles, causing rapid fatigue. The glycolytic system
Morrow Berberich
Cardiorespiratory System 1
will steadily begin in the instance of depleted substrate stores. Gastin (2001) provides tables and
figures reporting anaerobic versus aerobic energy contribution during single bouts of maximal
exercise at different durations. 94% of energy contribution during 0 to 10 seconds of maximal
exercise comes from anaerobic sources, while 6% comes from aerobic sources (Gastin, 2001).
Glycolysis is the second metabolic pathway that does not require the presence of oxygen
(Liberty University, 2022). The glycolytic system produces a net of 2 ATP, 2 NADH, and 2
pyruvate molecules. If oxygen is available, pyruvate can engage in aerobic metabolism to
produce ATP, making glycolysis the first step in carbohydrate degradation. The glycolytic energy
system provides energy for medium to high-intensity exercises from 10 seconds to 2 minutes. An
800m runner that finishes an 800m race in 2 minutes will use both anaerobic pathways, but
predominately glycolysis. 73% of energy contribution during 0 to 30 seconds of maximal
exercise comes from anaerobic sources, while 27% comes from aerobic sources (Gastin, 2001).
Oxidative phosphorylation involves the citric acid cycle and the electron transport chain,
which takes place in the mitochondria. The citric acid cycle breaks down pyruvate to form Co2
and acetyl CoA, which combines with oxaloacetic acid to form citric acid (Powers & Howley,
2021). The end products are 1 ATP, 3 NADH, 1 FADH2, and 2 CO2 molecules. The electron
transport chain (respiratory chain) uses high-energy electrons transported by NADH and FADH2
from glycolysis and the citric acid cycle to rephosphorylate adenosine diphosphate (ADP) to
produce ATP. This pathway is comprised of 4 protein complexes bound to the inner
mitochondrial membrane. Each complex pumps hydrogen ions (H+) from the matrix to the
intermembrane space, creating a large hydrogen ion gradient between the two compartments.
Hydrogen ions are pumped back into the mitochondrial matrix through the ATP synthase,
synthesizing ATP from ADP and organic phosphate.
Morrow Berberich
Cardiorespiratory System 1
Oxygen availability is important in aerobic metabolism because it is the final electron
acceptor to form H20, which maintains the hydrogen gradient and prevents the chain from being
blocked. A 10,000m distance runner that finishes a 10km race in 30 minutes will use a
combination of all 3 energy systems, but predominately oxidative phosphorylation. The aerobic
system provides energy for low-intensity exercise from 2 minutes to a few hours. 95% of the
energy required to perform a 10km race will come from aerobic sources and 5% will come from
anaerobic sources (Gastin, 2001). One glucose molecule produces 32 ATP molecules from
glycolysis and oxidative phosphorylation. The 3 phases involved in aerobic metabolism,
glycolysis, the citric acid cycle, and electron transport chain can switch back from one system to
another besides being only a forward process.
References
Blake, J. S., Munoz, K. D., & Volpe, S. (2019). Nutrition: From science to you (4th ed.). New
York: Pearson.
Gastin, P. B. (2001). Energy system interaction and relative contribution during maximal
exercise. Sports Medicine (Auckland, N.Z.), 31(10), 725–741.
https://doi.org/10.2165/00007256-200131100-00003
Liberty University. (2022, Fall). EXSC 510: Advanced Exercise Physiology. Week one, lecture
one: Bioenergetics and Metabolism. https://learn.liberty.edu
Powers, S. K., & Howley, E. T. (2021). Exercise physiology: Theory and application to fitness
and performance (11th ed.). McGraw-Hill. ISBN: 9781260237764
Morrow Berberich
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