Does post-tetanic potentiation compensate for low frequency fatigue?

The purpose of this study was to examine the effect of post-tetanic potentiation on low frequency fatigue in adult human quadriceps muscle. Sixteen subjects (10 male and six female) performed three 60 s sets of knee extension exercise in order to induce low frequency fatigue (reduction in torque output at 10 and 20 Hz). The potentiating stimulus (a 10 s maximal voluntary contraction) induced a 58% increase in twitch tension (Pt) during the pre-fatigue state. Immediately following the fatiguing exercise, torque (X +/- SE, Nm) at 10 and 20 Hz (submaximal transcutaneous stimulation, 50 microsecond pulses) decreased (P less than 0.05) from 54.8 +/- 5.8 and 94.9 +/- 9.6 to 40.3 +/- 6.1 and 77.0 +/- 11, respectively. Although potentiation at this time increased Pt from 40.9 +/- 4.0 to 54.8 +/- 3.7 (P less than 0.05), torque at 10 and 20 Hz was unaffected. At 60, 120 and 240 min post-contraction, torque at 10 and 20 Hz remained depressed. Following potentiation, which increased twitch tensions to between 64 and 75%, torque at 10 Hz was increased (P less than 0.05) at 60 min (36.3 +/- 4.1 vs. 50.7 +/- 6.2), 120 min (40.8 +/- 6.3 vs. 56.5 +/- 8.9) and 240 min (42.0 +/- 4.7 vs. 57.5 +/- 8.3) of recovery. Similar effects were also noted at 20 Hz. These findings indicate that post-tetanic potentiation can overcome the low frequency fatigue during the post-contraction period and restore torque to pre-exercise levels.