What term describes the gradual increase in contraction strength following rapid, repeated stimulation due to enzymatic warming?

• A. Treppe
• B. Wave/Temporal summation
• C. Incomplete tetanus
• D. Fused (complete) tetanus

Answer: (A)

The concept being tested is the staircase effect, known as Treppe. After rapid, repeated stimulation, a muscle’s contraction strength gradually increases with each twitch because heat from ongoing activity lightly warms the muscle. This warming speeds up enzyme reactions involved in metabolism and cross-bridge cycling, and it improves calcium handling, so each successive contraction can generate more force until a plateau is reached. This is different from wave (temporal) summation, where increased force comes from calcium buildup in the cytosol with less time for relaxation between stimuli. It also differs from incomplete tetanus, where partial relaxation still occurs between high-frequency stimuli, and from fused (complete) tetanus, where contractions fuse into a smooth, continuous contraction. Treppe specifically describes that stepwise rise in force due to enzymatic warming.