Which describes a greater degree of wave summation with a sustained, but quivering, contraction?

• A. Incomplete tetanus
• B. Treppe
• C. Fused (complete) tetanus
• D. Isometric contraction

Answer: (A)

Wave summation occurs when stimuli arrive before the previous contraction fully relaxes, increasing force with each pulse. An intermediate stimulation rate produces a sustained contraction that still shows small relaxations between stimuli, so the muscle looks tense but with a visible tremor. This describes incomplete tetanus, where there’s partial relaxation between waves that creates the quivering, not a completely smooth, fully fused contraction. If stimuli were even faster, the relaxation would disappear and you’d have fused (complete) tetanus—a smooth, continuous contraction. Treppe is the staircase rise in force with successive twitches after a rest, due to changes in calcium availability, not continuous summation. Isometric contraction is about force generation without length change and doesn’t specify the pattern of wave summation.