Comparison of two resistance training protocols, 6RM versus 12RM, to increase the 1RM in healthy young adults. A single-blind, randomized controlled trial.

Purpose: The purpose of the study is to compare the effect in healthy young adults of two resistance training protocols, six-repetition maximum (RM) versus 12RM on maximum strength (1RM).

Method: A single-blind, randomized controlled trial was used in the study. Sixty-two healthy physical therapy students, with age (mean [+standard deviation]) 23 (+2.6)  years, weight 67.4 (+11.7)  kg and height 171.7 (+8.4)  cm, of both genders who were recreationally active, but not training systematically, volunteered to participate in the study. They were randomized into two groups (group 1: 24 women and 8 men; group 2: 23 women and 7 men) by a block randomization procedure that ensured equal gender distribution. Sealed envelopes were used to conceal allocation to groups.

Interventions: Group 1 did three sets of 6RM of each exercise, and group 2 did three sets of 12RM. Both groups performed the exercises twice per week for 8 weeks with 3 minutes rest between sets and exercises. Primary outcomes were maximum strength defined as one-repetition maximum squat (1RMSq) for lower-body strength and bench press (1RMBp) for upper-body strength. Secondary outcomes were body weight and Uro Kaleva Kekkonen (UKK) Fitness Index.

Results: Both groups increased strength significantly (p < 0.001) in 1RMSq (6RM 13.6%, 12RM 13.5%) and 1RMBp (6RM 9.2%, 12RM 8.4%). There was no significant difference in the change between the two groups, no change in body weight and only a small increase in UKK Fitness Index.

Conclusion: Both 6RM and 12RM training protocols improve maximum strength in recreationally active healthy young adults, with no significant difference between the protocols.