Final answer:
Wave summation is the process where multiple temporally overlapping action potentials enhance muscle contraction, resulting in greater muscle tension than single action potentials. It can lead to incomplete tetanus with high-frequency stimulation, and with even higher frequencies, it may cause complete tetanus.
Step-by-step explanation:
When the influence of two or more temporally overlapping action potentials are 'added' together within a muscle, the phenomenon observed is called wave summation. This occurs because a second stimulus causes more Ca++ ions to be released, which then activates additional sarcomeres while the muscle is still experiencing a contraction from the first stimulus. The result of wave summation is an enhanced contraction of the motor unit, producing greater muscle tension than a single twitch.
If this pattern continues with increasing frequency, it can lead to incomplete tetanus, where there's a rapid cycle of contraction with short relaxation phases, and eventually, complete tetanus, where contractions become continuous due to the lack of relaxation phases.