The inspiratory muscle tension-time index T_T0.1 (given by P_0.1/P_Imax x T_I/T_TOT) could be used to reliably assess inspiratory muscle activity during exercise. So far, the correlation between the T_T0.1 and diaphragmatic activity has not been measured and the T_T0.1 has not been compared with other measurements of the inspiratory muscle load such as the transdiaphragmatic pressure index or TT_di. In this study we hypothesize that the T_T0.1 measuring the mouth is a noninvasive reflection of the electromyographic activity of the diaphragm. We simultaneously measured T_T0.1 and surface EMG (SEMG) of 8 trained subjects at rest and during incremental exercise. The curvature of T_T0.1 and the root mean square (RMS) follow the same trend during the incremental exercise with a significant correlation between T_T0.1 and surface EMG parameters (RMS; r = 0.81 p < 0.001 and MPF; r = 0.80 p < 0.001 respectively). We conclude that T_T0.1 measured as s an adequate noninvasive method reflects the diaphragmatic activity during incremental exercise in healthy subjects.