Seminar 5

Question 1

What is the role of ATP in muscle contraction

Answer 1

ATP is needed:
• To detach myosin from actin.
• To energize (cock) the myosin head.
• For calcium ion reuptake into the sarcoplasmic reticulum via ATP-driven pumps.

Question 2

Why does a 100-m Sprint Athlete Doesn’t Need High Mitochondrial Volume

Answer 2

• Sprinting relies on anaerobic energy systems: ATP-PCr and anaerobic glycolysis.
• These systems provide rapid ATP without the need for oxygen.
• Mitochondria are mainly involved in aerobic metabolism, which is slower.
• High mitochondrial density would not enhance performance for an event lasting ~10 seconds.

Question 3

Why a Marathon Can’t Be Run at Sprinting Intensity

Answer 3

•Sprinting requires anaerobic energy, producing ATP quickly but unsustainably.
•This leads to rapid fatigue due to lactate and hydrogen ion accumulation.
• Marathon running depends on aerobic metabolism, which is slower but sustainable.
• Oxygen delivery limits high-intensity output over long durations.

Question 4

Describe the different muscle fibre types

Answer 4

Type 1- high endurance, low f.orce, fatigue resistant
Type 2a- moderate endurance, moderate force
Type 2x- high force, low endurance, fatigues quickly

Question 5

What are the key enzyme concentrations in type 1

Answer 5

High citrate synthase and low PFK

Question 6

What are the key enzyme concentrations in type 2a

Answer 6

Intermediate levels of aerobic and glycolytic enzymes

Question 7

What are the key enzyme concentrations in type 2x

Answer 7

High PFK, low citrate synthase

Question 8

Which muscle fibre type is rich in mitochondria and oxidative enzymes

Answer 8

Type 1

Question 9

Which muscle fibre type is rich in glycolytic enzymes for rapid ATP production

Answer 9

Type2x

Question 10

How does Exercise Intensity Influences Substrate Selection

Answer 10

• Low intensity (25–40% VO₂max): Primarily uses fat.
• Moderate intensity (50–70%): Mix of fat and carbohydrates (CHO).
• High intensity (>75%): Predominantly carbohydrates due to faster ATP turnover and oxygen limitation.

Question 11

How does exercise duration influences substrate selection

Answer 11

• Short duration: Relies more on carbohydrates.
• Prolonged exercise (90+ minutes): Increases fat oxidation as glycogen depletes.
• Over time, the body shifts from glycogen to blood glucose and free fatty acids.

Question 12

How does Training Status Influences Substrate Selection

Answer 12

• Trained individuals:
o Greater mitochondrial density and oxidative enzymes.
o Better at oxidizing fats, sparing glycogen.
o Shift substrate use to fat at a given intensity compared to untrained individuals.

Question 13

Describe Nutritional Status and Substrate Use with exercise

Answer 13

• CHO consumed before/during exercise:
o Increases blood glucose availability.
o Suppresses fat oxidation due to increased insulin.
o Delays fatigue by maintaining glycogen stores.

Question 14

What are the Four Stages of Muscle Contraction Cycle

Answer 14

ATP binds to the myosin head causing myosin to lose affinity for actin.

Myosin bends with ATP, hydrolyses it, then binds to a new actin subunit.

Pi release triggers a neck shift. “Power stroke” returns myosin to its original shape.

ADP released to complete the cycle