Chapter 7: Macrostructure, Microstructure & Mechanics Of Skeletal Muscles

Question 1

• What are the 3 main types of muscles?
• What are the 4 functions of skeletal muscles?
• What is fascia?
• What are the 3 compartments in the thigh and the muscle group in each?
• What is epimysium and it’s 3 roles?
• Describe the anatomy of a skeletal muscle

Answer 1

1. Cardiac: involuntary, found only in the walls of the heart.
2. Smooth: involuntary muscle, found in internal organs.
3. Skeletal: voluntary muscle, making up the external muscles
   - Locomotion, limb movement, posture and joint stability.
   - Sheets of fibrous tissue that maintains groups of muscles.
   - Anterior compartment containing the quadriceps femoris, posterior compartment containing the hamstrings and medial compartment containing the adductors.
   - A fibrous tissue which covers the outside of the muscle, it’s roles are:
4. Transfer muscular tension to the bone through tendons so the application of force to the muscle is a smooth one.
5. Creates pathways for nerves and blood vessels.
6. Gives the muscle the ability to stretch and return to normal length.
   - The outermost layer of a muscle is the epimysium that holds together lots of fascicles. The outermost layer of a fascicle is perimysium that holds together lots of muscle fibres. Muscle fibre groups holds together lots of myofibrils, which contains sections known as sarcomeres. Sarcomeres contain thick (myosin) and thin (actin) filaments, together known as myofilaments which are the basic contractile units.

Question 2

• What 5 labels must be included in a diagram of a sarcomere?
• What happens to inactive and active muscles?
• What are the 5 main ideas in the sliding filament model?
• What happens when a nerve impulse arrives at the neuromuscular junction?
• what does the breakdown of ATP do in regards to the sliding filament model?

Answer 2

1. H zone: space between actin.
2. A bands: the myosin itself
3. I bands: space between myosin.
4. Z lines: boundaries of a sarcomere.
5. Actin and myosin filament.
   - Inactive muscle waste away (atrophy) whereas active muscle enlarge (hypertrophy)
   - H zone decrease, i bands decrease, A band stays the same, Z lines get closer and sarcomere shortens
   - Acetylcholine is released causing depolarisation of the motor end plate. This allows calcium to be released into the muscle, initiating a reaction between the myosin and actin in each muscle fibre. This will only occur if there are sufficient calcium ions and ATP available. (All or nothing law)
   - Enables the myosin heads on the myosin filaments to form cross bridges along the actin filaments, pulling the actin, shortening the sarcomere.

Question 3

• When nerve impulse at the neuromuscular junction ceases what happens, to the shortened sarcomere?
• According to the sliding filament model, how is force production produced?
• Describe the 3 types of muscle action.
• Name a benefit of concentric and eccentric contractions.

Answer 3

• The myosin heads relax their hold on the actin, allowing them to slide back to their relaxed position.
• By the number of myosin cross bridges to actin filaments. More cross bridges = more force produced.
  1. Isokinetic contraction: Muscle shortens at constant speed, occurs in agonist muscle and achieved through specialised machines. Closest sport example can be breaststroke, faster you increase speed of movements, resistance increases.
  2. Isometric contraction: muscle length remains same while tension increases. No movement of origin or insertion and occurs in fixator muscles.
  3. Isotonic contraction: muscle length changes while producing force. Can be concentric, where muscle and joint angle shortens under tension, occurring in agonist muscles. Or can be eccentric, where muscle lengthens under tension, occurring in antagonist muscle. only occurs if the antagonist is acting as a break to help control the joint movement. Eg TJ’s quads contract eccentrically each jump.
• Concentric contractions activate more muscle fibres but eccentric contractions recruit more fast twitch fibres.

Question 4

• Describe plyometrics
• Describe 4 advantages and disadvantages of isometric training?
• What are the 3 advantages and disadvantages of isotonic training?
• Using a exercise as an example, describe the 3 phases of muscle contraction.
• How does time affect muscle force?

Answer 4

• A form of exercise where a muscle is contracted eccentrically, followed by a concentric contraction.
• Ad: No equipment required, done anywhere, improves specific muscle strength and develops static strength. Dis: Muscle strengthens only at the angle used, doesn’t improve cardiovascular fitness, hard for cardiac problem suffers as blood flow to muscle stops and BP rises as less blood flows back to the heart and not sufficient on its own.
• Ad: Strengthens muscle throughout the range of movement, can choose exercises to match the actions in your sport and can exercise all major muscle groups. Dis: forces are uneven throughout exercise, muscle groups are not fully strengthened and can result in muscle soreness.
• Bicep curl: During upwards phase, the bicep gets shorter and fatter undergoing concentric contraction. When the weight is lowered, it lengthens undergoing eccentric contraction. When the weight is held steady, the biceps undergo isometric contraction.
• The shorter the time, the lower the force exerted and vice versa.

Question 5

• What are 3 advantages and 2 disadvantages of isokinetic training?
• Muscle force is affected by what 9 factors?
• Power is the combination of what?
• What are the 2 benefits of shorter and wider muscles?
• The force a muscle can resist increases when what?
• How much velocity is best for generating max power?
• Explain what is the best muscle length for peak force.
• Maximum force will occur more quickly if the tendon is tight or relaxed? Give a example in sport.

Answer 5

• Ad: Strengthens the entire muscle, exercises actual speeds of sports-specific activities and fastest way to gain strength. Dis: Needs specialised equipment and types of movement is limited.
• N° of muscle fibres recruited, muscle fibre type, cross-sectional area, joint angle, muscle shape, speed of contraction, type of muscle contraction, age and gender.
• Force and velocity
• Greater cross sectional area and so produces greater force (deltoids).
• Velocity of eccentric muscle length increases. eg a triple jumper can produce more force up, if the hamstring velocity is increased.
• 1/3 of maximum velocity
• Half way or at ‘resting’ length as a result of max binding of actin and myosin filaments. If the muscle length is too small, then the actins overlaps decreasing the n° of cross bridges. If muscle length were too long, there wouldn’t be enough cross bridges.
• Tight eg pre stretching before a race will loosen the tendons and therefore maximum force won’t occur as quickly.

Question 6

• The position of Damian Martin’s elbow shown in the image is considered to result in an optimal muscle length. Explain the force-length relationship of muscle contraction with respect to a very flexed, middle (as above) and very extended elbow joint.
• Explain the force-velocity relationship for concentric and eccentric muscle contractions when different magnitudes of force are required.
• The sport of netball requires athletes to jump explosively and sprint and repeat this for over an hour of game time. The athletes therefore play an intermittent type of game. Given such contrasting demands, name and justify the muscle type that may be most beneficial for these athletes and describe three characteristics of this fibre type.
• Describe the sliding filament theory with respect to the interaction between the actin and myosin filaments

Answer 6

• Force-length relationship relates to the amount of muscle force that can be produced at varying muscle lengths. At extreme lengths, flexed or extended, not as much force can be produced compared at middle length which is the optimum. This can be explained through the number of cross fridges that occur as different lengths.
• Force-velocity describes the relationship between force production and velocity of movement. For concentric actions, the relationship is inversely proportional where, as less velocity is required more force can be produced and vice verser. For eccentric actions, the relationship is proptional, as less force is required muscle velocity decreases and vice verser.
• Type 2a as they are explosive but are more fatigue resistant whereas type 2b are very explosive which is not required and fatigue too fast for netball. Characteristics of type 2a include: fast oxidative, fast contraction speed and high force capacity.
• With the release of calcium and break down of ATP into the muscle fibres, actin filaments reveals binding sites for the myosin heads to connect to forming cross bridges between the actin and myosin filaments. These cross bridges then pull the actin closer together to shorten the sarcomere and muscle.