‘Hitting the Wall’
• What is it?
• Why do you think it happens?
glucose
oxygen
carbon
dioxide
Aerobic
Respiration
Reminder
water
energy
glucose
oxygen
carbon
dioxide
water
energy
During anaerobic respiration, glucose breaks down into a
substance called lactic acid and some energy is released.
glucose
lactic
acid
energy
anaerobic = ‘without oxygen’
Anaerobic respiration involves the
incomplete breakdown of glucose and so
releases less energy than aerobic respiration.
Anaerobic respiration is useful to the body when energy
is needed in a hurry.
glucose
lactic
acid
energy
There are two problems with anaerobic respiration:
 Anaerobic respiration releases much less energy from
glucose compared to aerobic respiration.
 Lactic acid is a poisonous waste product.
Why is anaerobic respiration not the best way to get energy from
glucose?
During aerobic respiration, muscles get energy from glucose by
‘paying’ for it with oxygen.
glucose
oxygen
carbon
dioxide
water
energy
During anaerobic respiration, muscles get energy from glucose
but do not ‘pay’ for it with oxygen.
glucose
lactic
acid
energy
This means that an oxygen debt or Excess post-exercise oxygen
consumption (EPOC)is created.
When and how is this EPOC ‘paid off’?
Advantages of Anaerobic
Respiration
• Anaerobic respiration is useful for
muscle cells because it can release
energy to allow muscles to contract
when the heart and lungs cannot deliver
oxygen and glucose fast enough.
Disadvantages of Anaerobic
Respiration
• Anaerobic respiration releases much
less energy from each molecule of
glucose than anaerobic respiration.
• Lactic acid is not removed from the
body. It builds up in muscle and blood,
and must be broken down after
exercise.
The amount of blood circulated
by the heart depends on the
heart rate and volume of blood
pumped in each beat (stroke
volume)
cardiac output = stroke volume x heart rate
The cardiac output - volume of
blood circulated by the heart in
a given time
Calculate the Cardiac Output...
Cardiac Output
Stroke Volume
52
45
32
74
25
37
12
Heart Rate
67
72
76
54
58
78
92
Questions- Progress check
1. When someone is jogging they respire .................... (D)
2. But when someone starts to sprint they start to respire
.................... (C)
3. Why do they have to respire anaerobically? (C)
4. Respiring anaerobically means .................... is made. This can
cause the person to get cramp (C)
5. When they stop exercising their breathing does not return to
normal because they need .................... from the air to combine
with the lactic acid to get rid of it. (B)
6. Aerobic is more beneficial as it produces ________ energy than
anaerobic respiration. (B)
7. What is the term used to describe the process where your body
is “owed” oxygen? (A)
Answers
1. Aerobically
2. Anaerobically
3. Not receiving enough oxygen, so have to use
glucose directly to make energy (respire)
without oxygen.
4. Lactic Acid
5. Oxygen
6. More
7. Excess post-exercise oxygen consumption