$A$: Application of stimuli repeatedly just at the start of relaxation of a muscle fibre shows an increase in the extent of contraction initially and results in treppe or staircase phenomenon.
$R$: It can be attributed to the summation effect of the sub-threshold stimuli being given again and again.

  • A
    Assertion and Reason both are correct and also correct explanation.
  • B
    Assertion and Reason both are correct but not explanation of assertion.
  • C
    Assertion is correct,but Reason is incorrect.
  • D
    Both Assertion and Reason are incorrect.

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