Synchronous activation of motor units is attributed to common presynaptic input to motoneurons, and this is thought to increase the rate of rise of muscle force, and/or facilitate co‐activation of muscles. The inspiratory‐related drive to protrudor and retractor muscles of the tongue is associated with a rapid rate of rise of both EMG activity and force. Here, we examine the magnitude of synchronous discharge of co‐active motor unit pairs within genioglossus (GG, tongue protrudor), hyoglossus (HG, tongue retractor), and inspiratory intercostal (IC, rib cage expander) muscles in urethane‐anesthetized rats. We recorded from pairs of motor units that were spontaneously bursting under command of the respiratory central pattern generator. The strength of synchronous input to each pair was measured with cross correlation followed by the calculation of common input strength (CIS; frequency of synchronous action potentials in excess of those expected due to chance). CIS values for motor units within IC (N=9 pairs, 0.93 +/− 0.27) and tongue muscles (GG, 32 pairs, 0.83 +/− 0.11; HG, 41 pairs 0.67 +/− 0.13) were statistically equivalent. Across‐muscle CIS for tongue muscles was the same as the within muscle values (34 pairs, 0.55 +/− 0.1). CIS across GG and IC (10 pairs, 0.05 +/− 0.1) was less than within muscle values (P<0.01), while CIS between IC and HG was not (28 pairs, 0.29 +/− 0.1, P<0.05). In conclusion, the proportion of shared presynaptic inputs within and across the protrudor and retractor muscles of the rodent tongue is similar. In contrast, shared input to motor units of tongue and rib cage muscles is relatively low, which likely reflects drive from a different pool of premotor neurons.