COMEDK MDS entrance preparations | Increase force of muscle contraction

The force of muscle contraction can be increased by all of the following except:

A. Increasing the frequency of activation of motor units 

B. Increasing the number of motor units activated
C. Increasing the amplitude of action potentials in the motor neurons 
D. Recruiting larger motor units

 Ans. C 

Action potential follows an all or none law. If sufficient amplitude is reached to produces a response, increasing the amplitude further will not have any effect on the function to follow.

Factors responsible for grading of muscular activity

Number of motor units (Recruitment)	With minimal voluntary activity only a few motor units. With increasing voluntary effect more and more units are brought into play – ‘Recruitment phenomenon’. With increasing motor units, force of muscle contraction increases.
Frequency of contraction (Summation)	Frequency of discharge in the individual fibre play a role. Tension developed during a titanic contraction (with rapidly repeated stimulation) is greater than during individual twitches.
Large motor units	Force of contraction depend on length of muscle – Starling’s law