Without Fail: Muscular Adaptations in Single Set Resistance Training Performed to Failure or with Repetitions-in-Reserve.

METHODS Forty-two young, resistance-trained men and women were randomly assigned to 1 of 2 parallel groups: A group that trained to failure on all exercises (FAIL) or a submaximal effort group (2-RIR) that trained with two repetitions in reserve for the same exercises. Participants performed a single set of 9 exercises targeting all major muscle groups per session, twice weekly for 8 weeks. We assessed pre-post study changes in muscle thickness for the biceps brachii, triceps brachii, and quadriceps femoris, along with measures of muscular strength, power, endurance, and ability to estimate RIR in the bench press and squat. RESULTS Results indicated that both FAIL and 2-RIR elicited appreciable gains in most of the assessed outcomes. Several measures of hypertrophy tended to favor FAIL, although absolute differences between conditions were generally modest. Increases in countermovement jump height favored FAIL, but with no clear statistical support for either the null or alternative hypothesis. Increases in strength and local muscular endurance were similar between conditions. Participants demonstrated greater accuracy in estimating RIR for the bench press compared to the squat and improved their accuracy over the intervention, particularly for the bench press. CONCLUSIONS These findings suggest that single-set routines can be a time-efficient strategy for promoting muscular adaptations in resistance-trained individuals, even when transitioning from higher-volume programs. Training to failure in single-set routines may modestly enhance some measures of muscle hypertrophy and power, but not strength or local muscle endurance.