Bioenergetics (Lec 7)

Question 1

Energy Supply at Rest

Answer 1

• 2/3 from fats
• 1/3 from carbohydrates
• VO2 = 0.3L/min
• Blood lactate ~1mmol/L

Question 2

Determining Exercise Intensity

Answer 2

• Peak power (6s sprint)
• Anaerobic Capacity (30s wingate)
• % VO2 max
• Blood lactate concentration
• % Critical Power

Question 3

Steady State

Answer 3

Characterised by a stable VO2

• It takes at least 2-3mins for O2 consumption to stabilize to new, higher level exercise demands

Question 4

Limitations during Aerobic Exercise

Answer 4

Performance is limited by oxygen delivery and utilization

• VO2 = SV x a-vO2

Question 5

Blood Lactate

Answer 5

Marker of Glycolytic energy production

• Allows Glycolysis to continue

Question 6

Critical Power

Answer 6

CP is the power-asymptote

– i.e power that can be maintained ‘indefinitely’.

Question 7

CP and W’

Answer 7

• The W’, (pronounced w prime) represents a finite work capacity (J) available to the athlete once he or she attempts a power output above CP
– Is the curvature constant

Question 8

Above CP

Answer 8

Steady state is unable to be attained
– [PCr] decreases
– VO2 increases
– Muscle pH decreases

Question 9

Carbohydrates

Answer 9

• Primary fuel source for short duration, incremental or high intensity exercise
• During prolonged work (>30 min) there is a gradual shift from carbohydrate metabolism towards an increasing reliance on fat as a fuel substrate.

Question 10

Blood Glucose Homeostasis During Exercise: 4 Processes

Answer 10

1. Mobilisation of glucose from liver glycogen
2. Mobilisation of FFA (free fatty acids) from adipose tissue (Spares blood glucose)
3. Gluconeogenesis from amino acids, lactic acid, and glycerol
4. Blocking the entry of glucose into cells

Question 11

Blood Glucose Homeostasis During Exercise: Hormonal

Answer 11

Fast-acting
• Insulin, glucagon epinephrine, norepinephrine,

Slow-acting
• Cortisol, growth hormone

Question 12

Insulin and Glucose

Answer 12

Insulin increases cellular uptake of glucose
• Declines during exercise of increasing intensity and duration

Glucagon increases blood glucose
• Increased mobilisation of liver glycogen
• Increased liver glucose output
• Increased sensitivity of the liver to epinephrine

Question 13

Fat Metabolism

Answer 13

• First fat (triglyceride) must be broken down via lipase into FFA
• Then metabolised via β-Oxidation into 2 carbon chains and oxidised in the krebs cycle

Question 14

Regulation of Lipolysis

Answer 14

• Epinephrine, Norepinephrine and glucagon increase lipase activity promoting lipolysis
• During prolonged exercise insulin levels decline and epinephrine increases promoting higher level of fat metabolism

Question 15

Inhibition of Lipolysis

Answer 15

Mobilisation of FFA is inhibited by
– Insulin: Inhibits lipase activity, Decline in insulin during longer duration exercise results in increased FFA and glycogen sparing

– Lactate: High levels promote recombination of FFA and glycerol to form fats thereby decreasing the available FFA as fuel

Question 16

Hormone-Substrate Interaction

Answer 16

FFA mobilisation dependent on hormone sensitive lipase (HSL)
• FFA mobilisation decreases during heavy exercise( occurs in spite of persisting hormonal stimulation for FFA mobilisation)
• May be due to:
– High levels of lactic acid
– Elevated H+ concentration inhibits HSL
– Inadequate blood flow to adipose tissue

Question 17

Protein Metabolism

Answer 17

• Contribution to fuel supply may reach 15% depending on duration (2hrs+) and diet
• Skeletal muscle can directly metabolise some amino acids (AA) with the help of proteases
• Liver can convert alanine (an AA) into glucose