What is the term for the phenomenon when a second contraction develops greater tension if stimulated before complete relaxation?

The term describing the phenomenon in which a second contraction generates greater tension when a muscle is stimulated before it has fully relaxed is known as summation. Summation occurs when multiple stimuli are applied to a muscle, leading to an increase in the overall tension produced. This happens because the muscle fibers do not have enough time to completely relax between stimuli, causing the tension from preceding contractions to build upon the next contraction.

In this context, when a muscle is stimulated repeatedly, if the second stimulation occurs before the muscle has completely returned to its baseline tension, the force generated will be greater due to the additive effect of the tension generated by the first stimulation not fully dissipating. This is a common characteristic of muscle physiology and is critical in understanding how muscles generate force efficiently during activities that require sustained or rapid contractions.

The other options represent different phenomena: fused tetanus refers to a sustained muscle contraction that occurs when stimulation is frequent enough that the muscle does not relax at all between stimuli; the refractory period is the time following an action potential during which a new action potential cannot be initiated; muscle fatigue refers to the decline in the ability of a muscle to generate force, often after prolonged activity. Each of these concepts is distinct from summation, contributing to a complete understanding of