11. Metabolism in Exercise

Question 1

What are the benefits of exercise?

Answer 1

• Body composition changes ( less adipose, more muscle)
• Insulin sensitivity increases (diabetics!)
• Blood TAG decrease
• BP falls
• Psychological “well-being”
• Glucose tolerance improves (muscle glycogenesis increases)

Question 2

How do insulin levels change in response to a marathon?

Answer 2

Insulin levels fall slowly due to inhibition of secretion by adrenaline

Question 3

How do glucagon levels change when running a marathon?

Answer 3

Increase
Stimulates glycogenolysis
Stimulates gluconeogenesis
Stimulates lipolysis

Question 4

Which enzymes does glucagon stimulate to exert those effects?

Answer 4

PEPCK and fructose-1,6-BP - gluconeogenesis
Glycogen phosphorylase - glycogenolysis
Hormone sensitive lipase - Lipolysis

Question 5

Which hormone levels rise rapidly when undergoing exercise such as a marathon?

Answer 5

Adrenaline and growth hormone

Question 6

What does adrenaline stimulate?

Answer 6

Glycogenolysis and lipolysis

Question 7

What effect does growth hormone?

Answer 7

Mobilises fatty acids (lipolysis)

Question 8

What happens to cortisol levels over long, marathon-like exercise?

Answer 8

Slowly rise

Stimulates gluconeogenesis and lipolysis

Question 9

Which energy stores are the first to be used up during exercise?

Answer 9

ATP and creatine phosphate

Question 10

After ATP and creatine phosphate is used up, how does the muscle tissue release energy?

Answer 10

Anaerobic glycolysis of muscle glycogen (no increased delivery of oxygen yet)

Question 11

If longer duration of exercise, what happens after glycogen stores are used up?

Answer 11

Increased oxygen supply allows for aerobic oxidation of muscle glycogen, glucose and liver glycogen.

Question 12

In a marathon, what happens after glucose from liver glycogen is declining steadily (1 hour)?

Answer 12

Utilisation of fatty acids rises steadily after 30 minutes

Question 13

What 3 things are used during low intensity, long duration exercise?

Answer 13

Muscle glycogen
Liver glycogen
Fatty acids

Question 14

Which exercise type has the most aerobic activity?

Answer 14

Low intensity, long duration - marathon

Increased delivery of oxygen to tissues, whereas in a sprint this doesn’t happen in time.

Question 15

What happens to oxygen supply during moderate intensity exercise, e.g. 1500m?

Answer 15

Some extra oxygen can be delivered to tissues, but still 40% anaerobic metabolism.

Question 16

What are the 3 phases of moderate intensity exercise?

Answer 16

1. Initial start - creatine phosphate and ATP
2. Long middle - aerobic ATP production from muscle glycogen
3. Finishing sprint - anaerobic metabolism of glycogen, lactate producing

Question 17

What is the main energy supply in a 100m sprint (short, high intensity exercise)?

Answer 17

1. ATP and creatine phosphate
   Cannot deliver oxygen and nutrients in time…
2. Anaerobic ATP production of muscle glycogen
   Lactate build up leading to fatigue

Question 18

How long do creatine phosophate stores provide energy for?

Answer 18

5 seconds during a sprint

Question 19

Muscle glycogen can supply energy for how long during intensive exercise?

Answer 19

2 minutes

Question 20

What happens if exercise is low intensity?

Answer 20

Enough oxygen can be supplied for complete oxidation of glucose and glycogen stores (from muscle and liver) to last for around 60 minutes.

Question 21

When can fatty acids be used as a fuel during exercise?

Answer 21

Only in aerobic conditions

• slow release from adipose tissue
• Low rate of ATP production but high capacity for sustained production

Question 22

What is the cori cycle?

Answer 22

Liver recycles lactate:
Lactate produced from muscle cells is carried to the liver in the blood, where it is converted back to glucose and released into the circulation for uptake.

Question 23

How does exercise increase blood glucose concentration?

Answer 23

Increased gluconeogenesis

Increased glycogenolysis

Question 24

Which glucose transporters are present in muscle cells?

Answer 24

GLUT 4 (insulin dependent)
GLUT 1 - constitutively active

Question 25

What other glucose uptake process can muscle use during exercise?

Answer 25

Insulin independent uptake - increase in AMP stimulates AMPK which signals to increase GLUT4 translocation.