1. Explain how a muscle contracts according to the ‘sliding filament theory’. (4 marks)
1. Action potential reaches the motor end plate and causes depolarisation
2. This causes calcium ions to be released
3. The calcium ions attach to troponin
4. This moves/changes the tropomyosin complex
5. This leaves the binding sites on the actin free
6. Myosin heads attach to the actin binding site to form cross bridges
7. ATP required to form cross bridge
8. Myosin head moves towards the centre/power stroke occurs
9. Actin slides over the myosin/actin moves towards the centre of the sarcomere
10. Cross bridge then broken but can be recreated if calcium ions are still present
11. ATP is also required to allow the myosin to break the cross bridge

2. Action potential arrives down motor neurone to NMJ.
Wave of depolarisation spreads along Sarcolemma down T-Tubules to sarcoplasmic reticulum
Sarcoplasmic reticulum releases Ca2+ ions into the sarcoplasm.
Ca2+ binds to troponin causing it to change shape and move tropomyosin away from the actin binding sites
Myosin head (in an ‘energised state’ / position due to the breakdown of ATP) attaches to actin binding site forming a cross bridge.
(The release of ADP + Pi means that)The myosin head ‘cocks’ in a ratchet mechanism – the power stroke – moving the actin past the myosin
ATP binds to the myosin head detaching it from the Actin.
ATP breaks down into ADP + Pi, releasing energy returning the myosin head back to its energised position
Myosin head binds to the next actin binding site – process is repeated.
When the nerve impulse stops, Ca2+ is reabsorbed into the sarcoplasmic reticulum, so troponin moves tropomyosin over the actin binding sites again.
The heads bind independently of one another – each myosin head can bind and detach up to 100 times per sec. The myosin filaments have a large number of heads so during contraction they are all flicking to and fro – they do not all bind at the same time as this would make the sliding action jerky.

3. Types of Skeletal Muscle Fibre
Objectives:
Identify the structural features of Type I, IIa and IIb muscle fibres and relate that to their performance
Display likely %s of fibres used in different sports as a continuum
Justify an opinion on early fibre type identification in athletes.

4. Immunohistochemical fibre-typing stain for myosin heavy chain, slow type, in which type 1 fibres are brown. The eosin counter stain makes the type 2 fibres visible with a pink colour.
Three arrows indicate 3 type I muscle fibres

5. Types of Skeletal Muscle Fibre
Skeletal Muscle Fibres
Slow Twitch Fibres
(Type I Fibres) ST
Fast Twitch Fibres
(Type II Fibres)
Fast Oxidative Glycolytic Fibres Type IIa Fibres
FOG
Fast Glycolytic Fibres
Type IIb Fibres
FTG

6. Slow Twitch (Type I) Fast Twitch (Type II)
Red in colour
White in colour
Contract slowly
Contract Quickly
Aerobic
Anaerobic
Endurance Based
Strength/Speed based
Can contract repeatedly
Easily Exhausted
Exert less force
Exert great force

7. Type I Muscle Fibres Function:
Slow twitch fatigue resistant contractions. Required for endurance events
Adaptations:
Lots of Mitochondria
Lots of Myoglobin
High Capillary Density
High triglyceride stores
Small amount of fibres per neuron
Low anaerobic Capacity

8. Type IIa Muscle Fibres Function:
Fast Oxidative Glycolytic Fibres (F.O.G) – fast twitch fibres that have taken on some oxidative properties – more fatigue resistant than type IIb
Adaptations:
Some Mitochondria
Some Myoglobin
High Capillary Density
Large amount of fibres per neuron
Lots of glycolytic enzymes
Medium anaerobic capacity
Used in high intensity, medium duration activities eg 200m/ 400m sprints / 800m swim

9. Type IIb Muscle Fibres Function:
Fast Twitch Glycolytic Fibres (F.T.G) – fast twitch fibres that have taken on some oxidative properties – less fatigue resistant than type IIa
Adaptations:
Few Mitochondria
Little Myoglobin
Low Capillary Density
Large amount of fibres per neuron
Lots of glycolytic enzymes
High anaerobic capacity
Large PC stores
Fibres and neurons are larger and stronger. Used for power-lifting and short sprints

11. You must give an example of events and athletes.
Now, using your prior knowledge of energy systems link each muscle type with each energy system and explain how they will work together.
You must give an example of events and athletes.

12. Muscle type proportions
Fast and slow twitch fibre proportions vary in different muscles and different athletes.
These proportions tend to be inherited.
A marathon runner may have up to 80% slow twitch fibres in their leg muscles designed for long periods of aerobic work.
A sprinter may have the same % of fast twitch fibres which can generate high force, but may fatigue easily.

14. FIBRE TYPE RANGE IN SPORTS PERFORMERS
activity average % ST range of % ST
MALES
marathon
cross country skiers
cyclists
800m runners
untrained
shot putters
sprinters
FEMALES
cross country skiers
cyclists
800m runners
untrained
shot putters
sprinters
proportions of fibre types are genetically determined
this could account for specialisms of individuals

15. Imagine…
The British government is disappointed by the lack of medals won at the London 2012 Olympics.
A suggestion has been put forward that from 2013 all primary school children should have their major muscle groups (quads, gastroc, deltoids etc) tested to determine the % of different muscle fibre types that they have inherited.
Children would then be pushed to participate in sports that matched their fibre typing in order to have more athletes who are likely to achieve excellence.
List pros and cons of this idea and be ready to put your own thoughts forward.

16. Quick test
1. During a race, a swimmer has to dive off the starting blocks as quickly as possible. Identify the ‘muscle fibre type’ used to complete this action and justify your answer.
(3 marks)
2. Competing in the 100-metres at the World Athletic Championships or the Olympic Games provides the performer with both psychological and physiological challenges to overcome.
Figure 1 shows the proportions of different muscle fibre types for elite sprinters, elite middle distance runners and elite marathon runners.
Using Figure 1, which of the profiles, A, B or C, shows the proportions of muscle fibre types for elite sprinters? Justify your answer. (2 marks)
(b) Describe the characteristics of the main muscle fibre type used by elite sprinters. (4 marks)