Dias, MRC, Simao, RF, Saavedra, FJF, and Ratamess, NA. Influence of a personal trainer on self-selected loading during resistance exercise. J Strength Cond Res 31(7): 1925-1930, 2017-The purpose of this study was to compare differences in muscle strength and self-selected resistance training intensities between trained subjects who trained under the supervision of a personal trainer (PT) and those who trained without supervision (WoPT). Twenty-one trained subjects, men (n = 12) and women (n = 9), completed 3 sessions (separated by 48 hours) in the following sequence: first session, self-selected intensity assessment consisting of performance of 3 sets of 10 repetitions for the leg press (LP), bench press (BP), leg extension (LE), and arm curl (AC) exercises with self-selected load; second session, a 1 repetition maximum (1RM) test to determine subjects' maximal strength in the 4 exercises; and third session, a 10RM test to determine the maximum load completed for 10 repetitions for each exercise. Self-selected training loads were significantly higher in PT compared with WoPT for the LP (by 15.6%), BP (by 26.6%), LE (by 12.1%), and AC (by 22.2%) exercises. Self-selected training loads expressed relative to 1RM and 10RM data were significantly higher in PT (49-59.5% of 1RM; 62.7-77.3% of 10RM) than WoPT (41-58.7% of 1RM; 58.7-76.2% of 10RM) with largest difference observed in the lower-body exercises. Ratings of perceived exertion values were significantly higher in PT compared with WoPT. The results of the present study indicated that supervised resistance training with a personal trainer was advantageous in trained subjects although self-selected loading was still considerably lower than 1RM and 10RM percentage values.