Effects of ageing on the neuromuscular system

Question 1

Muscular strength across the lifespan

Answer 1

• Muscle mass and strength peak between 20 and 30 then plateau (until early 50s) then rapidly declines (60)

Question 2

Evidence of reductions in strength

Answer 2

• Strength in older population can be as low as 43% compared with young adults
• Lowest in females

Question 3

Failure of descending drive from motor cortex?

Answer 3

Twitch interpolation

• Stimulation of motor nerves produced no additional torque in majority of elderly men and women.
• Indicates that they remain able to utilise descending motor pathways for optimal muscle activation.

Question 4

Loss of muscle strength with increasing age

• Altered physical activity level
  
  • Physical activity and ageing

Answer 4

Tested at 75 and then 80
AA = constant active 
    * Maintained highest level strength 
SS = constant sedentary 
AS = decreased activity 
    * Greatest reduction in strength 
SA = increased activity

Question 5

Loss of muscle strength with increasing age

• Muscle atrophy
  
  • Muscle volume & cross-sectional area

Answer 5

Age associated with
- Reductions in muscle volume and cross-sectional are
- Increases in on-muscle tissue (fat & connective tissue)
- Lexell (1988): reduction in muscle mass of 40% between 20 and 80 yrs, began at 25 and 10% lost by 50yrs
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Question 6

Loss of muscle strength with increasing age

• Muscle atrophy
  
  • Muscle fibres: size, number & proportions

Answer 6

Type II (fast twitch) fibre size reduced with age (size of type I less affected)

• Difference in type II size in arms and leg (smaller in leg) -> difference in ageing process

Question 7

Loss of muscle strength with increasing age

• Muscle atrophy
  
  • Resistance training in elderly increases type II fibre size

Answer 7

• With resistance training, type II fibre size increase but not type I fibre

Question 8

Loss of muscle strength with increasing age

• Muscle atrophy
  
  • Muscle fibre: size, number & proportions

Answer 8

Number of fibres reduced with increasing age - accelerated loss after 60 yrs
Underlying mechanisms:
- Inactivity and immobilization
- Changes is functional demands for force, velocity and duration

Proportions

• Significant variability in proportion of type I fibres in older individuals
• Area of type II fibres combined was more strongly correlated with age than proportion of type II fibres or their mean size alone
• Therefore, in some muscles the reduction in are of type II fibres is due to reduction in number and in other muscles is due to a reduction in the size of the fibres

Question 9

Loss of muscle strength with increasing age

• Reduced number of motor units
  
  • Motor units and ageing

Answer 9

• Loss of alpha motor neurons (especially fast) from the spinal cord from the age of 60, with subsequent degeneration of their axons
• Reductions in number of functioning motor units -> increasing in size of remaining motor units (i.e. increase in number of muscle fibres per motor unit)