Abstract Objective We investigate the influence that inguinal fat has on maximal quadriceps response to femoral nerve magnetic stimulation. Methods Vastus lateralis M-wave amplitude and quadriceps twitch peak torque were measured (i) in lean and overweight subjects and (ii) when slices of pig fat ranging from 2 to 18 mm in thickness were placed between the coil and the nerve. Results In overweight group, the maximal response could not be elicited when intensity was ⩽90% and ⩽85% of maximal power for twitch torque and M-wave amplitude, respectively. The maximal response was obtained at 80% of maximal power in the lean group. Negative correlations between relative twitch torque changes and inguinal thickness were observed. Fat thickness altered quadriceps response at 14 mm and 8 mm in the lean and overweight groups, respectively. Conclusions The capacity of femoral nerve magnetic stimulation to deliver supramaximal stimulation is altered when fat thickness below the coil increases. Significance Special caution should be taken by clinicians when overweight or obese subjects are tested using femoral nerve magnetic stimulation.