Repetition numbers in resistance training: a comparison between the predetermined and the estimated repetitions to failure prescription approaches on affective responses

Background: In resistance-training, the number of repetitions is traditionally prescribed using a predetermined approach, whereby the numbers are decided upon before set initiation (e.g., three sets of 10 repetitions). An alternative is the estimated repetitions to failure (ERF) approach, whereby sets are terminated based on one's estimated proximity to task-failure (e.g., two repetitions before failure). The latter approach allows trainees to better account for day-to-day performance variability and may be perceived as a more enjoyable way to train. Methods: Twenty women (age range: 23-45 years) without resistance-training experience first completed estimated 1RM tests in four exercises. In the next two counterbalanced sessions, participants performed three sets of each exercise using 70%1RM. They either completed ten repetitions in all sets (predetermined condition) or terminated the sets when they perceived to be two repetitions before task-failure (ERF condition). Affective-valence, enjoyment, and approach-preference were collected during and after the sessions. Results: We observed trivial differences in the subjective measures and an approximately even approach-preferences split. Number of repetitions performed were mostly similar under both conditions in the chest-press, knee-extension and lat-pulldown (difference of ~1 repetition). However, under the ERF condition participants completed more repetitions in the leg-press (17 vs. 10, p<0.01). Conclusions: Both approaches led to comparable affective responses. However, the fact that participants performed a different number of repetitions across exercises while reaching a similar proximity to task-failure, suggests that the ERF approach may be preferable to account for day-to-day performance variability.