<prompt> The force of muscle contraction can be increased by all of the following except :Increasing the frequency of activation of motor unitsIncreasing the number of motor units activatedIncreasing the amplitude of action potentials in the motor neuronsRecruiting larger motor units  <response>: 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 voluntaryRecruitmenteffect 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 tetanicSummationcontraction with rapidly repeated stimulation is greater than during individual twitchesLarge motor unitsForce of contraction depends on length of muscle - starlings law 