Identify the current that leads to a tetanic contraction.

• A. Low Frequency Current
• B. High Frequency Current
• C. Both
• D. Neither

Answer: (A)

Tetanic contraction happens when stimulation is frequent enough that the muscle fibers don’t have time to relax between impulses. This requires a high-frequency current, because rapid pulses keep calcium levels high in the muscle fibers and maintain cross-bridge cycling, so the contractions fuse into one sustained, peak contraction. With low-frequency stimulation, each impulse causes a separate twitch and the muscle can fully relax between beats, so you don’t get a fused, tetanic contraction. In practice, therapists use higher frequencies (in the tens of hertz) to achieve a tetanus, while low frequencies produce individual twitches.