Does post‐tetanic potentiation compensate for low frequency fatigue?

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Abstract
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 (PP, 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.