Coexistence of peripheral potentiation and corticospinal inhibition following a conditioning contraction in human first dorsal interosseous muscle.

In skeletal muscle, post-activation potentiation (PAP) is observed following a conditioning contraction (CC) as a large (2- to 3-fold) increase in evoked twitch force and rate of force development (RFD). However, this enhancement has not been observed to occur during potentiated voluntary contractions. The purpose of this study was to determine if the lack of voluntary potentiation may be related to the development of central (corticospinal) inhibition. Participants (N=10, all males) completed voluntary and evoked index finger abduction contractions and transcranial magnetic stimulated (TMS) motor evoked potentials (MEP) of the motor cortex were recorded from the first dorsal interosseous (FDI). Central inhibition was assessed by measuring the silent period following the MEP. The FDI was potentiated via 10s conditioning contractions at 60% of maximal index finger abduction strength, using both voluntary and evoked tetanic contractions. Immediately following CC and transcutaneous electrical twitches. Following both voluntary and tetanic CC, force and RFD of the twitch were similarly increased (~200% and ~160% respectively). The silent period was elongated by ~10% following both forms of CC. These results indicate that corticospinal inhibition does occur following CC, but that it is unrelated to the voluntary activation during the CC. These results also show that following CC, the positive contractile effects at the muscle are concurrently accompanied by inhibitory effects at the corticospinal level.