Definition for Treppe
From Biology Forums Dictionary
1) If a skeletal muscle is stimulated a second time immediately after the relaxation phase has ended, the contraction that occurs will develop a slightly higher maximum tension than did the contraction after the first stimulation. The increase in peak tension will continue over the first 30–50 stimulations. Thereafter, the amount of tension produced will remain constant at roughly 25 percent of the maximal tension that would be produced in complete tetanus. Because the tension rises in stages, like the steps in a staircase, this phenomenon is called treppe, a German word meaning "stairs." The rise is thought to result from a gradual increase in the concentration of calcium ions in the sarcoplasm, in part because the ion pumps in the sarcoplasmic reticulum are unable to recapture them in the time between stimulations.
2) Treppe describes the phenomena where an increase in frequency of stimulation (with complete relaxation between pulses) will progressively increase the force developed by the muscle until force ultimately stabilizes. The explanation for this phenomena involves an increasing concentration of intracellular calcium, due to incomplete removal of calcium during relaxation, which elevates the force developed by the muscle cell. Summation of contraction is observed as the frequency of stimulation increases further, such that the muscle cell does not completely relax between twitches. As the frequency of twitches increases, the first twitch will not completely relax before the second twitch arrives, and so on. Thus, as frequency increases, the force generated by the muscle would continue to increase until a maximum is reached.