Aim: 

Posttetanic potentiation (PTP) is usually estimated by measuring the peak twitch (Pt) increase and is typical in fast-twitch fibers. Mechanomyogram (MMG) has been recently added to force signal analysis to monitor changes in muscle contractile function due to fatigue, demonstrating a parallel reduction in MMG peak-to-peak (MMGpp) and Pt. Scarce data are retrievable regarding MMG behavior in enhanced muscle function conditions.

The aim was to evaluate the changes in the mechanical responses (force, MMG) due to PTP in different human leg muscle types.

Methods: 

Force (by a loadcell) and MMG (by an accelerometer) signals, in dominant tibialis anterior (TA) and vastus lateralis (VL) of 10 healthy male subjects during transcutaneous supramaximal stimulation, has been recorded. The potentiation protocol was modified by Lee and Binder-Macleod (2000). Single twitch (ST) contractile parameters, pre- and post-PTP, were analyzed: Pt, contraction time (CT), plus MMGpp.

Results: 

The following averaged relative changes resulted after potentiation: Pt +8.9±12.9%, CT -5.5±10.1%, MMGpp +17.2±6.1% for TA; Pt +20.1±12.5%, CT -8.8±19.2%, MMGpp +35.9±14.8% for VL.

Conclusions: 

Both VL and TA showed twitch response enhancement (greater for VL) due to PTP. In particular, the enhancement resulted more evident for MMGpp than force Pt, indicating a specific and not yet investigated aspect of the potentiation phenomenon in human muscles.