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

C i.e. Increasing the amplitude of action potential in the motor neurons.Action potential follows an all or none law. If sufficient amplitude is reached to produces a response, increasing the amplitude fuher will not have any effect on the function to follow.Factors res onsible for gradingof muscular activityNumber of motor unitsWith minimal voluntary activity only a few motor units discharge. With increasing voluntary(Recruitment)effect more and more units are brought into play - 'Recruitment phenomenon'. With increasing motor units, force of muscle contraction increasesFrequency of ContractionFrequency of discharge in the individual fibre play a role. Tension developed during a tetanic(Summation)contraction (with rapidly repeated stimulation) is greater than during individual twitchesLarge motor unitsForce of contraction depends on length of muscle - starling's law