Does post-tetanic potentiation compensate for low frequency fatigue?

Summary. 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 μs pulses) decreased (P<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 P, from 40·9 ± 4·0 to 54·8 ± 3·7 (P<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<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.