Although there is consensus that the central nervous system mediates the increases in maximal voluntary force (MVC) produced by resistance exercise, the involvement of the primary motor cortex (M1) in these processes remains controversial. We hypothesized that 1-Hz repetitive transcranial magnetic stimulation (rTMS) of M1 during resistance training would diminish strength gains. Forty subjects were divided equally into 5 groups. Subjects voluntarily (VOL) abducted the first dorsal interosseus (FDI) (5 bouts x 10 repetitions, 10 sessions, 4 weeks) at 70-80% MVC. Another group also exercised but in the 1-minute-long inter-bout rest intervals received rTMS (VOL+rTMS, 1 Hz, FDI motor area, 300 pulses per session, 120% of the resting motor threshold, rMT). Group 3 also exercised and received sham rTMS (VOL+SHAM). Group 4 received only rTMS (rTMS_only). The 37.5% and 33.3% gains in MVC in VOL and VOL+SHAM, respectively, were greater (p = 0.001) than the 18.9% gain in VOL+rTMS, 1.9% in rTMS_only, and 2.6% in unexercised Controls who received no stimulation. Acutely, within Sessions 5 and 10, single-pulse TMS revealed that motor evoked potential size and recruitment curve slopes were reduced in VOL+rTMS and rTMS_only and accumulated to chronic reductions by Session 10. There were no changes in rMT, maximum compound action potential amplitude (Mmax), and peripherally evoked twitch forces in the trained FDI and the untrained abductor digiti minimi. Although contributions from spinal sources cannot be excluded, the data suggest that M1 may play a role in mediating neural adaptations to strength training.