Auxotonic contraction of a muscle is:

Auxotonic contraction: is the one in which the strength of contraction goes increasing, as the contraction proceeds. This phenomenon is about a single contraction. As the contraction proceeds, more and more motor units may be recruited in the contraction, thus increasing the strength of contraction.This is in skeletal muscle. Staircase phenomenon: is phenomenon for multiple contractions;in which the strength of contraction goes increasing in successive contractions.