The purpose of this study was to investigate the effects of short rest intervals normally associated with hypertrophy-type training versus long rest intervals traditionally used in strength-type training on muscular adaptations in a cohort of young, experienced lifters. Twenty-one young resistance-trained men were randomly assigned to either a group that performed a resistance training (RT) program with 1-minute rest intervals (SHORT) or a group that employed 3-minute rest intervals (LONG). All other RT variables were held constant. The study period lasted 8 weeks with subjects performing 3 total body workouts a week comprised of 3 sets of 8-12 repetition maximum (RM) of 7 different exercises per session. Testing was carried out pre- and post-study for muscle strength (1RM bench press and back squat), muscle endurance (50% 1RM bench press to failure), and muscle thickness of the elbow flexors, triceps brachii, and quadriceps femoris via ultrasound imaging. Maximal strength was significantly greater for both 1RM squat and bench press for LONG compared to SHORT. Muscle thickness was significantly greater for LONG compared to SHORT in the anterior thigh and a trend for greater increases was noted in the triceps brachii,(p = 0.06) as well. Both groups saw significant increases in local upper body muscle endurance with no significant differences noted between groups. The present study provides evidence that longer rest periods promote greater increases in muscle strength and hypertrophy in young resistance-trained men.