Muscles and exercise (wk5)

Question 1

Describe muscular and neural factors responsible for gains in strength:

Answer 1

-Change in pennation angle -> Changes in pennation angle may help to increase force as there will be more muscle fibres/unit of muscle volume. There are also more cross-bridges and more sarcomeres in parallel.
> Sarcomeres in series -> displacement and velocity. Sarcomeres in parallel -> force.
> Greater pennation in the muscle -> greater hypertrophy
> Force output = total fibre CSA x Cosine angle of pinnation
-EMG = Neural activity. Over 6 months, the muscle mass keeps on increasing, even though the changes in strength originate from neural activity are over the first 2 months. This means that strength in the long-term originates from muscular factors.

Question 2

Explain the mechanisms of hypertrophy:
-Use graph from 23/10

Answer 2

-Hypertrophy -> Increase in muscle fibre size. Due to the addition of contractile proteins in the muscle cell. Protein synthesis (greater than) > protein breakdown
-Depends on -> Initial strength, duration of training program and training technique
-Hyperplasia -> Increase in the number of muscle fibres. There is evidence of hyperplasia in animals, but not humans. However, there is not enough evidence to support hyperplasia in humans.
-Resistance training components -> Time-under-tension, intensity, sets, reps, velocity (of contractions), exercise order, recovery between sets, frequency, exercise type
-Repetition maximum contraction = 1 Rep Max

Question 3

Describe the molecular mechanisms responsible for gains in muscle mass:
-Satellite cell proliferation

Answer 3

-Satellite cell proliferation -> Muscle has small injuries which activate the fibres. Activated and aggregate the injury there is. There is then fusion to the damaged myofiber and an alignment and fusion to produce new myofibers. This regenerates the myofiber with the central nuclei. This increases the muscle size (hypertrophy).
-Satellite cells proliferate following muscle trauma and form new myofibers through a process similar to foetal muscle development. After several cell divisions, the satellite cells begin to fuse with the damages myotubes and undergo further differentiations and maturation.

Question 4

Describe the molecular mechanisms responsible for gains in muscle mass

Answer 4

-m TOR (mammalian target of rapamycin), protein synthesis and ribosomal biogenesis
-Extracellular pro-hypertrophic signals -> hormones and growth factors
-Muscle protein balance -> Anabolism v Catabolism. Anabolism has a greater rate of muscle protein synthesis (MPS) over muscle protein breakdown (MPB), whereas catabolism has a greater rate of MPB over MPS. Muscle protein is in a constant state of turnover. The body is continuously balancing MPS and MPB. MPS -> Food (combined essential amino acids and insulin response) and exercise. MPB -> Starvation, stress, injury/illness and exercise.

-Muscle-fibre type proportions and shifting -> Muscle-fibre type proportion varies across sports. Type 2 fibres have greater potential for hypertrophy. Type 1 fibres have greater aerobic capacity. Research has shown changes from type 2a to type 2b and vice-versa. Changes from type 1 to type 2 fibres and vice-versa is less clear.
-Specific muscle-fibre hypertrophic potential -> Low-load exercises can activate type 2 fibres only if performed until volitional fatigue. This could increase muscle fibres size due to the higher potential of type 2 fibres to hypertrophy.

Question 5

Describe whole-muscle and fibre-type adaptations to resistance (strength) training:

Answer 5

-ACSA -> area perpendicular to a muscle’s longitudinal axis
-PCSA -> Muscle mass x cosine of the pennation angle / fibre length x muscle density
-Changes in muscle from training -> Pennation, muscle fibres, fascicle length
-Uneven distribution of whole-muscle hypertrophy -> Muscle mass can be increased differently

Question 6

Describe whole-muscle and fibre-type adaptations to resistance (strength) training
-Hypertrophy focus

Answer 6

-Hypertrophy between different muscle groups -> Upper body appears to elicit greater hypertrophy with resistance training. This can be due to; habitual loading of lower extremities and fibre-type composition.
-Influence of gender -> Women have (roughly) 60-80% strength, fibre and muscle CSA of men. Absolute changes in strength and muscle mass with resistance training is greater for men. Relative change in strength/mass is similar between genders.
-Time-course changes in muscle morphology. Morphological changes seen from 3rd week.