Comparison of quadriceps inactivation between nerve and muscle stimulation.

We evaluated the use of direct muscle stimulation for quantifying quadriceps inactivation at different contraction levels as opposed to conventional twitch interpolation using nerve stimulation. Fourteen healthy volunteers were tested. Paired stimuli were delivered to the femoral nerve or to the quadriceps muscle belly during voluntary contractions ranging from 20% to 100% of maximum, and the amplitude of the superimposed doublet was quantified to investigate inactivation. Superimposed doublet for muscle and nerve stimulation, respectively between the range of 60% to 100% of maximum (e.g., at 100%, muscle stimulation was 14 ± 5 Nm and nerve stimulation was 15 ± 6 Nm). Despite higher current doses, muscle stimulation was associated with less discomfort than nerve stimulation (P < 0.05). Collectively, our data suggest that direct muscle stimulation could be used to assess quadriceps inactivation at maximal and quasi-maximal contraction levels as a valid alternative to motor nerve stimulation.