Which phenomenon is described by a gradual increase in contraction strength with rapid stimuli, reflecting the muscle's warming up and enzyme efficiency improvements?

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

Answer: (A)

The staircase pattern of contraction strength, known as treppe, shows a resting muscle producing progressively stronger contractions with successive identical stimuli as it warms up. Each twitch becomes stronger because the slight rise in temperature enhances enzyme activity and calcium handling inside the muscle. Calcium is more readily released from the sarcoplasmic reticulum and the cross-bridge cycles operate more efficiently, so force increases with each stimulus until the muscle reaches a new steady state. This is distinct from phenomena caused by very rapid, overlapping stimuli, where contractions merge (temporal summation and tetanus) rather than simply improving due to warming.